This is only a preview of the October 2024 issue of Silicon Chip. You can view 45 of the 112 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Items relevant to "3D Printer Filament Dryer, Part 1":
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OCTOBER 2024
ISSN 1030-2662
10
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Contents
Vol.37, No.10
October 2024
12 The life of Nikola Tesla, Part 1
Nikola Tesla was a prolific inventor, engineer, futurist, essayist and the
original ‘mad scientist’. In this two part series we will cover his many
(significant) contributions to society.
By Dr David Maddison, VK3DSM
Biographical feature
The MIPI I3C Bus
Feature: Page 28
Page 44
28 The new MIPI I3C Bus standard
I3C (Improved Inter-Integrated Circuit) is one of the more recent serial bus
standards supplementing I2C and SPI. This article compares I3C to the
older standards, and explains what new functionality has been added.
By Andrew Levido
Digital interfaces
54 MG4 XPower Electric Car
The MG4 XPower is a mid-sized battery-powered electric hatchback. After
nine months and 20,000km with the MG4 XPower, is it any good?
Review By Julian Edgar
Electric vehicles
8-Channel Learning
IR Remote Receiver
PAGE 82
63 1-24V USB Power Supply
The Zk-DP is an inexpensive supply module that converts 5V DC to any
voltage from 1 to 24V DC at up to 3W.
By Jim Rowe
Using electronic modules
20 3D Printer Filament Dryer, Part 1
Store up to four 1kg reels of 3D printer filament in this Drying Chamber. The
filament can then be fed straight to your printer from a small hole in its lid.
By Phil Prosser
3D printer accessory
44 8Ch Learning Remote Receiver
This eight-channel relay board can be controlled by nearly any IR remote
control. Each output on the relay board can be set to toggle on/off, be
switched on for a fixed period or stay on while the button is held down.
By John Clarke
Remote control project
66 Jaycar-sponsored Mini Projects
This month we have a WiFi relay remote control, and an analog servo gauge
which converts an analog voltage to a dial readout.
By Tim Blythman
Mini projects
72 Dual-Rail Load Protector
This project disconnects a load from its power supply if the voltage is
reversed or too high or if the current is above the adjustable trip level. It
works with audio amplifiers, or other devices rated from ±4-36V DC.
By Stefan Keller-Tuberg
Power supply project
82 Micromite Explore 40
The Explore 40 (also called the Explore-40) is a Micromite in the same form
factor as Raspberry Pi Pico boards. It allows you to build designs intended
to use a Pi Pico but program them in Micromite Basic.
By Tim Blythman
Microcontroller project
MICROMITE
EXPLORE-40
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Editorial Viewpoint
There are still TDM TLAs
The phrase “TDM TLAs” (too darn many three-letter
acronyms) was coined back around 1990 to describe
the ridiculous number of three-letter abbreviations
floating around. Since then, the problem has only
gotten worse.
Sometimes when I’m reading press releases or news
articles, I’m forced to use Google to try to decode the
gobbledygook presented to me. It isn’t helped by the
fact that for any given set of three letters, there are probably a dozen (or more)
possible meanings. It isn’t always easy to figure out which one the writer is
referring to from context!
Take, for example, DRM. If I wrote that DRM was bad (or DRM was good),
what would that mean to you? Am I referring to Digital Rights Management?
Digital Radio Mondiale? Disaster and Risk Management? Document and
Record Management? Design Rules Manual? Design Review Meeting?
Department of Resource Management? Data Recovery Module? (I could go on!)
Did the folks who decided to call it Digital Radio Mondiale really want it
to be confused with something that has negative connotations like Digital
Rights Management? They could at least have called it Mondiale Digital Radio;
MDR does refer to other things already, but nowhere near as many as DRM.
In our articles, we try to spell out any term before we introduce its
abbreviation. For example, if we introduce the concept of a digital-to-analog
converter (DAC), then later we refer to a DAC, the reader should be able to
understand what we mean. It’s when these things come out of the blue, and
often in groups, that they can be perplexing.
Here’s an example of a real sentence someone apparently wrote that I
found online:
Our team is using a CI pipeline with a new API to improve our POC for
the CRM integration, but we ran into issues with the DNS when configuring
the TLS settings. The devs are also considering switching the DB to a more
robust SQL solution after some KPI analysis showed lag in the UX.
Did you get that?
Even if you’re familiar with some IT terms like CRM, TLS and SQL, you
probably won’t know all of those terms, and you’ll have to go off searching
for a while before you can decode that sentence. It’s really only helpful to
experts in the field, so if you’re writing like that, you’d better be sure of who
your audience is.
It certainly doesn’t help that some of those terms have multiple meanings.
For example, POC can be Point of Contact, Proof of Concept, Power Converter
and some other, less flattering things (similar to POS).
I have a sinking feeling that regardless of what I write here, the overcrowded
list of abbreviations is only going to grow with time. Still, perhaps by ‘raising
awareness’, we can work together to resist this scourge on our language.
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Collection of SC & EA magazines available in New Zealand
My father (John Caudwell), a longtime tinkerer/repairer
and subscriber of your magazine, recently passed away.
He had accumulated a large collection of magazines from
1983 to 2024, being Electronics Australia up to 2000 and
Silicon Chip from then on. The family has donated them
to a charity in Whakatāne that can be contacted at:
crew<at>pouwhakaaro.co.nz
www.crewonline.org.nz
Derek Caudwell, Tauranga, New Zealand.
Old valve-based test equipment
I recall reading about some home-made oscilloscopes
in recent pages of Silicon Chip. I recovered Dad’s RF Output Waveform Scope from under the house. Switching it
on, the CRT spot appeared on the screen; I don’t know
if it had an internal timebase generator. Dad passed in
1994, aged 90.
I think the origins of these instruments would date back
to the 1950s, to Radio & Hobbies magazine. The L/C Bridge
with the Magic Eye certainly would. I wonder if the ‘scope
would be of interest to Mr Batty. I also have his Grid Dip
Oscillator, with a cast aluminium handle branded VK3MX,
in a protective cover. The coil set is somewhere, too.
I’m just a little younger than Jamieson ‘Jim’ Rowe, who
recently retired. I still have his book, “An Introduction to
Digital Electronics”, in pristine condition.
Robert Sebire, Emerald, Vic.
Neutral vs Earth in domestic mains wiring
After reading Mr Pierson’s article on an extension lead
repair (Serviceman, August 2024), I have been prompted to
mention my unusual experience with installing a GPO in
an older house here in Germany. I also came across a projector that had its plug replaced incorrectly due to poorly
thought-out colour-coding of the wires.
I was asked to replace a broken power socket in an older
house here. The electrical installation regulations are
much less stringent than in Australia & NZ, which makes
me rather question whether the laws in Australia are perhaps a bit over the top sometimes. Anyway, I was allowed
to tackle the task without needing certificates etc, so I set
about investigating the situation in more detail.
When I opened the wall socket, I noticed something
unusual that was the norm here until about 30 years ago.
To save wire, the regulations used to allow you to connect
the Earth pin of the GPO to the mains Neutral conductor,
rather than having a separate Earth conductor.
The Neutral conductor is Earthed at the switchboard via
various Earthing rods and water pipes etc (as in Australia).
As long as that connection is intact (which is naturally a
big assumption), it should still work OK.
If the Neutral-Earth connection at the switchboard is not
intact, the Neutral conductor should still be more-or-less at
Earth potential anyway. If a device somewhere else in the
house has a short to the ‘Earth’, a fuse should still blow.
Otherwise, there is the danger that all the devices in your
house are suddenly at 230V potential, which is probably
not a good thing. Plenty of assumptions here!
Anyway, virtually all houses here built before about 1979
have their GPOs connected this way and I have never heard
of a problem. I would be interested in what your readers
think about this configuration, which, thankfully, has now
been discontinued.
So, to get back to my GPO replacement, I cheerfully went
about installing a proper Earth wire and noticed that the
Photos provided by Robert Sebire showing his father with his home-made radios and test equipment.
siliconchip.com.au
Australia's electronics magazine
October 2024 5
Neutral wire was red. Gasp! Another interesting German
anomaly.
For some unbelievably stupid reason, the Active wires
in these older houses were black and the Neutral & Earth
(if it existed) wires were red.
The danger lurking here is obvious, as my experience
with a slide projector I was given demonstrates. It didn’t
seem to work properly and was prone to giving shocks
sometimes. So I was asked to give it the once-over and see
where and what the concern was.
Well, it had a normal power cord with three conductors,
as one would expect. My first check concentrated on the
new plug that had recently been fitted as a replacement for
an old, broken plug.
When I opened the plug up, I noticed that, in keeping
with the older colour coding, the wires were coloured red,
red and black. How would you connect them to a new plug?
Perhaps logically, the owner had attached the red & red
wires to the power pins, and the black to Earth.
What he didn’t know was that one of the red wires was
the Earth and was connected to the projector housing! It
was quite extraordinary that he was not killed in the middle of a slide show.
As the plugs here are not polarised, depending on how
he plugged the projector in, its metal housing was either
close to Earth or at 230V. Of course, I fitted a new power
cord with the correct colour coding.
To return to my GPO, I left the red wires in place as they
were in conduit in the wall and served other plugs and
devices. However, I connected the Earth pin of the new
GPO to a separate Earth conductor that I installed from the
switchboard to the socket. This was still no remedy for the
many other sockets in that house that continue using the
(red!) Neutral wire as Earth.
The main thing is that the owner is happy with his
repaired GPO.
Christopher Ross, Tübingen, Germany.
Comment: using red for both Neutral & Earth (even if
they will sometimes run via the same wire to the GPO) is
a baffling decision; especially since in the old Australian
scheme, which was probably used elsewhere, red indicated Active!
Soldering SMDs not as difficult as first thought
Thank you for your recent project of an Automatic LQ
meter in the July 2024 edition of Silicon Chip (siliconchip.
au/Article/16321).
At first, I was reluctant to start a project using SMD
components. Being an old-school TV Tech from the 1970s,
it looked to be a difficult project.
I decided to have a go anyway, and was pleased with the
result. Soldering the SMD components was easier than I
thought, even though a few expletives were mumbled when
the components moved out of position when holding them
down ready for soldering.
The main problem I found was identifying the writing
on the components, even with a magnifying light. I did,
however, have success with taking a close up photo with
my phone and then zooming in on the photo.
Programming the Nano was also easy, and I was thrilled
when I switched on the power to the LQ Meter and it worked
perfectly first time! A photo of the finished device is shown
at the lower left of this page.
I urge anybody who is a bit reluctant to use these components to give it a go. It’s well worth it.
Neville Bell, Wangaratta, Vic.
Smartphones listen to your conversations
I just received the June 2024 issue in the mail and have
the following comment about privacy phones.
While in earshot of an unattended smart phone, a mate
and I had a detailed discussion about camel testes for a bit
of fun. The resulting targeted marketing was hilarious; however, the phone’s owner was not amused! She was awakened
to the ads she was receiving and as to why.
After an incident that she described as ‘creepy’, I was
asked about improving privacy on her older HTC-brand
phone. As a well-known technician, I am expected to know
everything about anything technical, but I had been able to
avoid modern smartphones, so knew very little.
I cherish my tiny Nokia 208 which, combined with the
Nokia PC Suite on my Toshiba Tecra A-10, is an amazing
device that allows me to do incredible tasks. I am certain
that if Nokia produced an updated version, they could
dominate the market again. The impending demise of the
3G network will force me to embrace ‘modern’ phone technology, so I took on the task to redeem myself and to learn.
After some research, I settled on a Google Pixel 6 Pro
phone on which I loaded GrapheneOS via the website. I
easily transferred her contact list via a CSV file. The phone
is very responsive, with a good battery life and takes excellent photos.
I also set up her social media on her laptop with Firefox
and Facebook Container to limit prying. She now feels safe,
and I have redeemed myself for my initial mischief.
I am preparing a replacement for my beloved Nokia; however, I live off-grid in an old shack where the only service
is 3G and there has been no discussion of any 4G being
provided to the area. With no NBN fixed or wireless services, and my ADSL service being recently discontinued,
I anticipate a very quiet lifestyle.
Chris Ryan, Dubbo, NSW.
Date of TV shop photo and the fate of Stromberg-Carlson
The finished LQ Meter assembled by Neville Bell. It was his
first project involving SMDs.
6
Silicon Chip
In the September issue, on page 74, the caption for the
second photo on the left states it is “An HMV radio and
television display circa 1969.” The picture depicts some
17-inch E1 or E2 TVs (a disaster for EMI, by the way) that
were last produced in 1957. The rest of the TVs are from the
F-series, which commenced in 1957. So the photo would
presumably have been taken in 1957.
Australia's electronics magazine
siliconchip.com.au
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Also, in Vintage Radio on page 106, there is a statement
that Stromberg-Carlson failed because it was not competitive in the TV market. That is quite untrue. They designed
all their TVs in Australia and they were a good-performing,
reliable product that incorporated many unique construction innovations and sold well.
What killed Stromberg-Carlson was the twin effects of a
huge bad debt from a major retailer (HG Palmer), who were
actually trading insolvent, and the government-imposed
credit squeeze of 1961. You can read about the fall of HG
Palmer (apparently also due to the credit squeeze) in the
Australian Financial Review at siliconchip.au/link/ac18
Henry Gordon Palmer was later sentenced for issuing
a false prospectus, and was a guest of Her Majesty at the
Malabar Mansions for a time.
There was actually a connection between Stromberg-
Carlson and Radio, TV & Hobbies magazine. Their early-
1960s electronic organ project started as a Stromberg-
Carlson product for HG Palmer. I think it was made possible by the liquidation of the company.
Ian Robertson, Belrose, NSW.
Comment: regarding the photo, Kevin Poulter is checking
his records to see if he can shed any light on the apparent
misdating. It may be that the description for that photo
was mixed up with another one.
Regarding Stromberg-Carlson, Assoc. Prof. Graham
Parslow points out that Admiral also went bust as a result
of HG Palmer’s business strategy but AWA survived, so
some TV manufacturers fared better than others.
Keeping hands safe while using a sharp knife
Thank you for another interesting project in the Styloclone musical instrument (August 2024; siliconchip.au/
Article/16415). I am currently getting parts to make it and
looking forward to getting it singing. I will add it to my Skill
Tester timber base, so there will be a kind of matching pair.
One comment regarding your suggestion of a mesh glove
for cutting. Another of my interests is bookbinding, which
involves using a strong, very sharp blade to cut paper and
thick card. After a couple of attempts to sever my left thumb
(it’s never been quite the same!), I invested in a couple of
safety steel rulers.
One is the Maun Metal Safety Ruler, which has an
M-shaped profile; your fingers are protected inside the
central depression. Another is an anonymous type with a
lift-up flap that protects your fingers. That might make it a
bit easier to keep the cut straight than using a metal glove.
David Coggins, Beachmere, Qld.
Single-valve radio has room for improvement
Thanks to Ian Batty for the kind words about the single-
valve radio project (Mailbag, September 2024, page 6). That
whole project really taught me a lot about the practical
aspects of feedback, positive and negative. However, there
is still another drop to squeeze out of the lemon!
I wanted to implement ‘reaction’ feedback to the tuning
coil as well, but ran out of time and the will to continue.
You will note in the photo of the under chassis (July 2024,
page 83) the aerial coil has a bunch of odd windings left
on it. Some of that is the unused reaction coil.
Having used reaction in another project and found out
how much the overall gain and selectivity of a tuning stage
can be improved, it would have been the ‘cherry on the
8
Silicon Chip
Australia's electronics magazine
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cake’. The improvement can be about the same effect as adding another tuned low-gain stage, and that is sorely needed
in this one-valve radio. Perhaps one day I may revive the
project and give it some more time.
On the subject of running out of time, I wonder how
many contributors or readers are in my age group. I passed
the 80 mark in May this year and still run a workshop covering all sorts of hobbies, mechanical and electrical. Even
if you are approaching invalid status, as I am, your brain
still needs exercising; you can achieve a lot just shuffling
around a workshop, slowly but surely.
The lesson here to the guys and girls of this age is that
you are never too old to learn and to make stuff. I wonder
what the average age of readers and contributors is.
Fred Lever, Toongabbie, NSW.
Solar/wind vs nuclear power
I read Kelvin Jones’ letter in Silicon Chip (page 12, July
2024). Coincidentally, an article from The Conversation
by Peter Martin appeared on the ABC site, titled “When
it comes to power, solar could leave nuclear and everything else in the shade” (siliconchip.au/link/abyt). A few
salient quotes:
“Whereas nuclear power is barely growing, and is shrinking as a proportion of global power output, The Economist
reported solar power was growing so quickly it was set to
become the biggest source of electricity on the planet by
the mid-2030s.”
“Installed solar capacity is doubling every three years,
meaning it has grown tenfold in the past 10 years. The Economist says the next tenfold increase will be the equivalent
of multiplying the world’s entire fleet of nuclear reactors by
eight, in less time than it usually takes to build one of them.”
Perhaps the main reason is cost, and Martin delivers a
quote from The Economist to help explain:
As the cumulative production of a manufactured good
increases, costs go down. As costs go down, demand goes
up. As demand goes up, production increases — and costs
go down further.
The main argument raised against solar is that the sun
doesn’t always shine. Martin writes:
[T]he efficiency of batteries is soaring and the price is
plummeting, meaning that on one estimate the cost of a
kilowatt-hour of battery storage has fallen by 99 per cent
over the past 30 years.
Australia’s energy market operator says record generation from grid-scale renewables and rooftop solar is pushing down wholesale electricity prices.
Meanwhile, at The Conversation (and not yet at the ABC
site), “Australia’s ‘carbon budget’ may blow out by 40%
under the Coalition’s nuclear energy plan – and that’s the
best-case scenario” (siliconchip.au/link/abyu).
According to various “energy experts”, including the
likes of CSIRO and AEMO, The Dutton Plan for seven
nuclear reactors will come online too late to make up for
the closure of coal plants with the prospect of blowing out
our carbon budget by 40%, and will contribute only somewhere in the vicinity of 10% of the country’s energy needs
all at enormous cost.
The Dutton Plan is not so much a nuclear plan but a gas
plan, probably to please some of his party’s donors. Meanwhile, renewables are expanding at a frightening pace and
getting cheaper all the time. Martin writes: “In 2023, China
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Australia's electronics magazine
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Despite the completely-broken screen, this laptop still
worked using an external display.
installed as much solar capacity as the entire world did in
2022.” Furthermore, in The Guardian, Graham Readfearn
casts doubt on Dick Smith’s pronouncements, saying, “but
CSIRO analysis shows his argument in meltdown” (see
siliconchip.au/link/abyv).
Backing nuclear power in preference to renewables
is simply poor economic policy. Anybody nailing their
colours to the mast of nuclear energy will see renewable
alternatives overtaking them based mostly on cost, that is,
the relative cheapness of renewables compared to nuclear
and fossil fuels. After all, sunshine is free.
Australia doesn’t even have a nuclear industry to speak
of, so all the palaver about costs and projected timelines for
completion is not much more than optimistic speculation.
Phil Denniss, Darlington, NSW.
How much punishment can a laptop take?
I just read the July 2024 issue, and one of the first articles I read in each issue is Serviceman’s Log. This time,
Dave tells of the trials of bringing equipment back from the
dead, which hits a bit too close to home.
A few weeks ago, my local Amateur Radio Club had a
break-in. There wasn’t a lot of damage, except for how the
vandals got in. All of our fire extinguishers had been let
off and the powder was spread throughout the club rooms,
with food and drink cans left behind as well. Quite a mess,
to say the least.
One thing that was severely damaged was a little laptop
computer. It was used by a few of the members from time
to time. It was connected to a television so we could use
it for the occasional presentation.
The people that broke in decided to take their anger out
on this little laptop and damage the screen beyond repair.
We all thought it was ready for recycling, but I decided to
try and see if it would boot up.
Firing up the television (thankfully it was not damaged)
and changing over to the correct HDMI input, all of a sudden, the laptop display appeared on the TV screen. Except
for the ruined screen, we couldn’t find any other problems.
It looks like it will live another day!
Stephen Gorin, Bracknell, Tas.
SC
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Australia's electronics magazine
October 2024 11
1856–1943
Nikola
Tesla
the original ‘mad scientist’
B
efitting someone who made such
contributions, he was said to
have been born during a violent
lightning storm at midnight between
July 9th and 10th, 1856, in Croatia.
According to his family, the midwife
said the lightning was a “bad omen”
and that he would be a “child of darkness”, to which the mother replied,
“No. He will be a child of light.”
Fortunately, he became a force for
good and lived for 87 years. He passed
away in 1943, leaving a remarkable
and world-changing legacy, which we
will now examine.
Of his numerous inventions & developments, among the most important were his contributions to threephase AC electricity, the induction
motor, the Tesla coil (used in many
early radios) and one of the world’s
first hydroelectric power plants. The
development of three-phase electricity
allowed the transmission of electrical
power over long distances, one basis of
modern industrial civilisation.
The electric car company Tesla is
named after him. Two museums are
dedicated to him, and there are statues
of him on Goat Island, USA and Queen
Victoria Park, Canada, both near Niagara Falls. There are also several Tesla
memorial plaques in Manhattan, New
York, USA.
Tesla’s thought processes
Tesla on the cover of Electrical Inventor magazine, February 1919. The lead
image is based on a photo of Tesla from around 1900 demonstrating wireless
power transmission. He is holding a partially evacuated glass bulb that’s
glowing due to the electric field from a nearby Tesla coil. See https://w.wiki/
AZMz
Tesla’s creative genius might be
attributable to his unusual thought
processes. These facilitated his ability to visualise and create things. He
wrote in Electrical Experimenter, February 1919:
In my boyhood I suffered from a
peculiar affliction due to the appearance of images, often accompanied by
strong flashes of light, which marred
the sight of real objects and interfered
with my thought and action. They were
pictures of things and scenes which I
had really seen, never of those I imagined... I was quite unable to distinguish
whether what I saw was tangible or not.
Then I observed to my delight that I
could visualize with the greatest facility. I needed no models, drawings or
experiments. I could picture them all
as real in my mind. Thus I have been
led unconsciously to evolve what I consider a new method of materializing
inventive concepts and ideas, which is
radically opposite to the purely experimental and... so much more expeditious and efficient.
Australia's electronics magazine
siliconchip.com.au
Nikola Tesla was a prolific inventor, engineer,
futurist and essayist. He spoke eight languages,
had a wide range of interests and has been
described as a “Renaissance man”. Despite his
‘mad scientist’ vibe, his contributions to our
modern industrial civilisation are significant.
Part 1 by Dr David Maddison, VK3DSM
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Silicon Chip
... My method is different. I do not
rush into actual work. When I get an
idea I start at once building it up in
my imagination. I change the construction, make improvements and operate
the device in my mind. It is absolutely
immaterial to me whether I run my turbine in thought or test it in my shop. I
even note if it is out of balance. There
is no difference whatever, the results
are the same.
In this way I am able to rapidly
develop and perfect a conception without touching anything. When I have
gone so far as to embody in the invention every possible improvement I can
think of and see no fault anywhere, I
put into concrete form this final product of my brain. Invariably my device
works as I conceived that it should,
and the experiment comes out exactly
as I planned it.
Also, like many creative geniuses,
he had various eccentricities.
Tesla, mathematics and
quantitative theories
Tesla was different from most other
scientists and engineers. His writings
are highly descriptive and contain few
equations. He was a visual thinker
and performed mathematics ‘visually’
rather than presenting it through formal methods.
He also did not accept Maxwell’s
equations, which are the basis of
electricity, magnetism and optics.
(“We can no longer believe in the
Maxwellian hypothesis of transversal ether-undulations and the literal
truth of its corollaries.” – siliconchip.
au/link/aby0).
He generally ignored quantitative
theories; it has been suggested he may
have suffered from “mathematical
aphasia”. His work was experimental, usually practical, descriptive and
not analytical. In that respect, he was
much like Michael Faraday; it was
Maxwell who turned Faraday’s intuitive ideas into equations.
Separating fact from fiction
While Tesla’s contributions to technology were undoubtedly outstanding,
it should be recognised that work has
been attributed to Tesla that either he
did not originate or where he was a
partial contributor.
Also, during his lifetime, there was
fierce commercial competition regarding which electrical supply technology
was to be adopted, so there were often
siliconchip.com.au
An American postage stamp
featuring Nikola Tesla. Source:
https://postalmuseum.si.edu/
object/npm_2008.2007.74
claims and counterclaims made
that didn’t necessarily reflect the
reality of who invented what.
Tesla had no marketing department; he had to do his own promotion, which is often reflected in his
writing style.
Not all of Tesla’s inventions or ideas
were successful or viable. Tesla’s
early work, such as with the induction motor, generators and the Tesla
coil was excellent. However, some of
his later work, which involved long-
distance wireless electricity transmission, was not based on sound physical
principles.
Tesla’s patents
Tesla was prolific and obtained
around 112 US patents, 29 UK patents
and six Canadian patents. He applied
for 33 patents that were not granted.
He also had patents in other countries
for a total of around 300; for a complete
list, see https://w.wiki/AZLY
Tesla’s life and career
We will now take a look at some of
Tesla’s milestones in chronological
order. This article will end in 1897;
the remainder will be covered in the
second and final article in this series,
to be published next month.
University
1875 to 1878
Tesla studied engineering from September 1875 at the Graz University
of Technology in Austria but, having
started with excellent results, did not
finish his degree. He left after the first
semester of the third year, apparently
losing interest in his studies while
spending too much time in a café and
associated activities.
He sat no exams that year and was
excluded. While at university, he saw
a Gramme dynamo, which operated
either as a generator or motor. He conceived a way to eliminate the commutator, which his professor didn’t
believe was possible.
This ultimately led to Tesla’s development of the AC induction motor,
which contains no commutators. He
received an honorary doctorate from
Graz in 1937.
Prague
1880
Tesla arrived in Prague and spent
much of his time reading at the Klementinum Library and Národní
Interesting facts about Nikola Tesla
● He had a great sense of humour.
● He was a rival of Edison, not a sworn enemy; they had a mutual respect
for each other.
● He had the idea of a ‘smartphone’ type device in 1901. He described to his
then-backer J.P. Morgan a handheld device he said would deliver stock
quotes and telegram messages.
● For unknown reasons, he hated pearls and would not speak to any lady
wearing them.
● He had a photographic memory.
● He had a fear of germs, always wore white gloves and rarely shook hands.
● He asked for large numbers of napkins at meals.
● He never stayed in a room or floor number divisible by three.
● He ran his life according to a strict daily schedule.
● He was very particular about dress and grooming.
● He had a beloved pet pigeon.
● The SI unit for magnetic flux is named after him, the Tesla (T).
● Toward the end of his career, he ran out of profitable ideas, or at least people
who were prepared to back him financially. As a result, he passed away in
poverty with many unpaid debts.
Australia's electronics magazine
October 2024 13
Kavárna café. He also attended lectures at the University of Prague but
was not enrolled as a student.
magnetic field combined to create the
AC induction motor.
Budapest Telephone Exchange
1883
1881
In 1881, Tesla commenced work
with the Budapest Telephone
Exchange, a new company that was
not yet functional. So he helped set
it up, as a draftsman and later chief
electrician, making several design
improvements.
Continental Edison Company
1882
In 1882, Tesla worked for Edison
in Europe. He started by installing
lighting systems, but his expertise
was noted, and he became involved
in designing improved dynamos and
motors.
Rotating magnetic fields
1882
The idea of a rotating magnetic
field was conceived as early as 1824
by François Arago but, according to
Tesla, he conceived of its use in an AC
electric motor while walking through a
park in Budapest in 1882 (documented
on p198 of the PDF at siliconchip.au/
link/aby0).
Although he doesn’t explicitly mention the rotating magnetic field, it was
the basis of the motor. His idea of eliminating commutators and the rotating
Prototype induction motor
In 1883, while working for Edison in
Strasbourg, he constructed (on his own
time) an induction motor but could not
find any interest in it.
Emigration to the USA
1884
Tesla’s manager in Europe was
recalled back to Edison in the USA
and requested Tesla to come to work
at the Edison Machine Works in New
York City. There, he managed staff
involved in installing New York’s electricity utilities. He was also involved
in developing an arc lamp street lighting system, but that needed high voltages and was incompatible with the
Edison system.
Tesla’s designs were not utilised;
there had been improvements in
incandescent lighting. Tesla only
worked there for six months before he
left, apparently after a dispute about
an alleged promised bonus.
Tesla Electric Light & Manufacturing
1885
After leaving Edison, investors
asked Tesla to design a system of electric arc lamps for lighting the streets of
New York and other cities. This led to
the establishment of the Tesla Electric
What is polyphase electricity?
Many early writings on AC electricity use the term “polyphase”. Polyphase
refers to an AC electrical system with two or more AC voltage supplies
supplied by separate wires and with the sinewaves of each displaced from
each other by a certain amount, usually described in degrees. Early work
on polyphase systems was with two phases, but today, three phases is the
most common configuration.
A three-phase system is twice as efficient at conductor utilisation as
a single-phase system. Polyphase power, especially three-phase, is ideal
for induction motors, as it can easily generate a rotating magnetic field,
eliminating high-maintenance commutators and allowing simple and
inexpensive construction.
The principle of a rotating
magnetic field in a threephase induction motor. The
magnetic field sequentially
rotates between the various
motor poles, causing the rotor
to follow it and rotate.
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Australia's electronics magazine
Light and Manufacturing Company.
Tesla continued obtaining patents
for motors, generators and other equipment, but the investors showed no
interest in those. They decided manufacturing was too competitive and just
wanted to run an electric utility. They
left the company, which left Tesla
penniless; worse, he had assigned
his patents to them in return for the
now-worthless stock. He described it
as “the hardest blow” he ever received.
Digging ditches
1886 to 1887
After the failure of his company, he
made a living digging ditches.
Labs in New York
1887 to 1902
During this period, Tesla maintained
a series of laboratories in Manhattan,
New York. They were on Liberty Street
(1887-1889), Grand Street (1889-92),
South Fifth Avenue (1892-95) and East
Houston Street(1895-1902).
The Tesla Electric Company
1887
In 1887, with new investors, Tesla
set up the Tesla Electric Company
and the Liberty Street laboratory. In
the same year, he invented an induction motor (patented in 1888) that
would run on the newly developed
AC system. It was becoming popular
in Europe because of its advantages of
long-distance transmission with little
electrical loss.
The motor used polyphase current
which, at the time, was two-phase
(we have three now). The polyphase
current generated a rotating magnetic
field. The advantage of this motor was
that it did not need a commutator,
which caused sparks, required high
maintenance, and was expensive and
complex. Apart from motors, Tesla
developed generators and other power
system devices.
Polyphase induction motor patent
1888
In 1888, Tesla obtained US patent
381,968, the first of a series on electric
motors (it continued until 1896). It was
for commutator-free polyphase alternating current induction motors (see
Fig.1). He envisaged two- and threephase motors in that patent.
He also published descriptions of
other motors, including a synchronous
motor for which the rotation speed is
locked to the AC power frequency.
Those are ideal for clocks and other
motors where precise speed control
is essential.
siliconchip.com.au
induction and other types of electric
motors and generators.
Independently wealthy
1889
Tesla became independently
wealthy due to Westinghouse licensing his patents, so he had the funds
from 1889 to pursue his own interests. It has been suggested that Tesla
was not a particularly good businessman and was always looking for
investors, unlike Edison. Also, Tesla
tended to work for himself, while Edison employed many other people and
had multiple projects on the go at once.
Wireless lighting
1890
Fig.1: a model of Tesla’s first induction motor at the Tesla Museum, Belgrade,
Serbia. Source: https://w.wiki/AZM$
Galileo Ferraris independently
invented and demonstrated a commutator-free two-phase alternating current induction motor in 1885, but he
didn’t patent it because he could see
no practical application.
royalty clause on the motors and he
later purchased the patent. The cancellation of the royalty clause meant
that Tesla would get a minute amount
of the true value of his motor and generator patents.
Westinghouse
Polyphase current and generators
George Westinghouse of the Westinghouse Electric & Manufacturing
Company was already marketing an
AC power system and needed a suitable AC motor. He considered using
Ferraris’ motor but decided that Tesla’s was superior.
Tesla’s investors negotiated with
Westinghouse in 1888 to license his
AC transformer, dynamo and motor
designs for cash and stock plus a royalty per horsepower of AC motor sold.
He also hired Tesla as a consultant for
a hefty fee.
During 1888, there was intense
competition between the three main
electrical companies: Westinghouse,
Edison and the Thomson-Houston
Electric Company. There was also
the emerging “war of the currents”
between the AC system promoted by
Westinghouse and the DC system promoted by Edison.
Tesla’s motor was not immediately
successful, and the adoption of the
polyphase AC system was limited. The
intense competition meant that Westinghouse did not have the resources to
continue to develop Tesla’s induction
motor or the polyphase AC system.
Westinghouse was then in serious financial trouble. He explained
the difficulties to Tesla, and in 1891,
Tesla released Westinghouse from the
The first of two important patents
this year was US patent 390,413 for a
“System of Electrical Distribution” for
electrical transmission of polyphase
power such that “two or more circuits
may have a single return path or wire
in common”.
The second was US patent 390,414
on a “Dynamo Electric machine” concerning adapting existing dynamos
easily and cheaply to polyphase alternating current.
1888
siliconchip.com.au
1888
A large number of patents
1888 to 1891
This period was enormously productive for Tesla; many patents were
granted, including 43 US patents in the
area of single and polyphase currents,
In 1890, Tesla started experimenting
with wireless lighting and performed
public demonstrations with power
transmitted by inductive or capacitive coupling. This work continued
for about another ten years.
Tesla coil
1891
In 1891, Tesla patented a type of resonant transformer that is now known
as the Tesla coil (US patent 454,622).
A resonant transformer uses capacitors
across one or more windings, which
act as coupled resonant tuned circuits.
It produces high-voltage, low-current,
pulsed or AC electricity at radio frequencies. Voltages produced can range
from 50kV to millions of volts at 50kHz
to 1MHz.
The essential elements of a Tesla
coil are an air-cored ‘oscillation transformer’, a capacitor, a high voltage
primary transformer and a spark gap.
Tesla used these coils in numerous experiments and built them to
very large sizes, such as in Colorado
and Wardenclyffe. Experiments Tesla
used the coils for included investigating biological effects, high-frequency
phenomena, lighting (for which the
Fig.2: Tesla
giving a
demonstration of
wireless power
transmission in
1891. Source:
https://w.wiki/
AZN2
Australia's electronics magazine
October 2024 15
original patent was issued), phosphorescence, radio, wireless power transmission and X-rays.
Tesla made a radio antenna out of
the high-voltage end of the secondary
part of the transformer, turning it into
a radio transmitter. Such an arrangement was used in most early sparkgap radios for wireless telegraphy
applications until the 1920s, when the
vacuum tube rendered them obsolete.
Lighting power supply
1891
In 1891, he applied for and was
granted US Patent 454,622 for a
means of generating high-voltage and
high-frequency electricity for lighting
purposes.
Incandescents & power transmission
1891
In this year, he obtained US Patent
455,069 for an incandescent light. On
May 20th, Tesla demonstrated wireless
power transmission to the American
Institute of Engineers in a lecture hall
at Columbia University. The lecture
was entitled “Experiments with alternate currents of very high frequency
and their application to methods of
artificial illumination”.
In one demonstration, he vertically
suspended two large zinc sheets from
the ceiling, which were connected to
a high-frequency, high-voltage Tesla
coil. He held an unconnected gasfilled tube between them, and the
tube glowed due to the electrostatic
field between the sheets, just as a fluorescent tube glows when near a high-
voltage power line due to capacitive
coupling.
Wireless power transmission
1891 to 1898
Tesla’s dream was global wireless
electrical transmission. From 1891 to
1898, he performed numerous experiments and demonstrations in wireless
Fig.4: in Tesla’s design, two single-phase alternators were magnetically coupled,
90° out-of-phase to provide two-phase AC for the exposition lighting. Note the
alternator’s size in relation to the man. Source: https://historicpittsburgh.org/
islandora/object/pitt:20170320-hpichswp-0011
transmission via capacitive or inductive coupling (see Fig.2). In 1899, he
commenced larger-scale experiments
at Colorado Springs and later Wardenclyffe.
AIEE organisation
1892 to 1894
From 1892 to 1894, he was vice
president of the American Institute
of Electrical Engineers, a forerunner
of the IEEE.
Visit to Europe
1892
He gave a series of lectures in London and Paris on “Experiments with
alternate currents of high potential and
high frequency”.
Chicago World’s Fair
1893
Also called the World’s Columbian
Exposition, was a significant turning
point in the “war of the currents”, with
Fig.3: nighttime lighting
at the 1893
Chicago
World’s Fair
using Tesla’s
patented AC
and lighting
systems.
Source:
https://w.wiki/
AZN3
George Westinghouse winning the
lighting contract ($399,000) over Edison’s DC system ($554,000) – see Fig.3.
Westinghouse used Tesla’s AC
power patents to power lighting of
their own design (they could not use
Edison’s lights). The lighting and other
systems at the fair used twelve 745kW
60Hz single-phase AC generators of
Tesla’s design. These were mounted
in pairs and arranged to provide twophase power (see Fig.4).
The Westinghouse Company also
had a section showcasing Tesla’s
inventions, such as induction motors
(Fig.5) and generators. The rotating magnetic field used in induction
motors was demonstrated with the
“Egg of Columbus” (Fig.7).
Tesla demonstrated wireless lighting using neon tubes, although he did
not invent neon lighting (see Fig.6).
He also demonstrated clocks synchronised to the mains frequency.
Talks at Franklin Institute & NELA
1893
His talk was “On light and other
high frequency phenomena” and he
mentioned the “transmission of intelligible signals and power to any distance without the use of wires” (radio).
He also discussed the idea of transferring power over long distances through
the Earth.
Niagara Falls hydroelectric power
1893
In 1893, Tesla was invited to consult for the Niagara Falls hydroelectric
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siliconchip.com.au
Fig.5: an exhibition of Tesla’s motors
and the “Egg of Columbus” at the
1893 Chicago World’s Fair. Source:
https://w.wiki/AZN4
►
Fig.6: Tesla’s wireless lighting
demonstration using neon tubes at the
Chicago World’s Fair.
project. Proposals that had been put
forward for the electrical system
included two- and three-phase AC and
high-voltage DC.
Tesla advised that a two-phase AC
system from Westinghouse, designed
by Tesla and based on his patents, was
the best and most reliable option (see
Fig.9). Westinghouse was awarded the
main contract based on Tesla’s advice
and the success of the Tesla and Westinghouse displays and lighting system
at the Columbian Exposition.
Nine of the twelve patents used for
the plant’s machinery were Tesla’s.
Electricity from the plant first went to
a nearby factory in 1895 and then to
Buffalo, New York, in 1896.
At a talk about the City of Buffalo
receiving power from Niagara on January 12th, 1897, at the Ellicott Club,
Tesla said:
It is a monument worthy of our
scientific age, a true monument of
enlightenment and of peace. It signifies the subjugation of natural forces to
the service of man, the discontinuance
of barbarous methods, the relieving
of millions from want and suffering.
From “The Age of Electricity” by
Nikola Tesla, Cassiers Magazine –
London, March 1897, pp378-386.
This AC power plant is regarded as
the final victory of the “war of the currents”, with Tesla’s AC proving itself
superior to Edison’s DC.
A low frequency of 25Hz was chosen, as it was expected that much of the
Fig.7: a drawing of the “Egg of Columbus” that was designed to demonstrate the
rotating magnetic field devised by Tesla. Source: https://w.wiki/AZN5
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Australia's electronics magazine
power would be converted to DC via
rotary converters for uses such as aluminium production. However, it was
realised that three-phase power was
superior for transmission efficiency,
so phase-changing transformers were
used to convert the two-phase power
to three-phase.
These are known as “Scott-T” transformers since they were invented by
Charles F. Scott, who worked for Westinghouse in the late 1890s. The configuration of this type of transformer is
shown in Fig.12. The first output phase
(0°) is a direct transformer-
coupled
copy of the first input phase (0°) via
transformer T1.
The second phase at 120° is generated by connecting the centre tap of
Fig.8: a drawing of Tesla lecturing
before the French Physical Society
and The International Society of
Electricians in the 1880s.
October 2024 17
Fig.9: ten 3.7MW 25Hz 2kV
Westinghouse generators at
Edward Dean Adams Power
Plant in Niagara Falls,
installed in 1895. The voltage
was stepped up to 10kV or
20kV depending upon how
far away the destination was.
These generators remained
in use until 1961. Source:
https://w.wiki/AZN6
Fig.10: the “unipolar vacuum
tube” comprising a glass bulb
(b), a single electrode (e) and
a lead-in conductor (c). A
second electrode could be
added towards the bottom;
otherwise, the return circuit
was via capacitive coupling
through the air. Source:
Tesla Universe – siliconchip.
au/link/abyf
T1’s secondary to the lower (90°) end
of T2’s secondary and adding a tap at
√3 ÷ 2 or 86.6% of T2’s secondary. The
third phase requires no extra connections to generate as the 240° waveform
is simply available as 360° − 120° (360°
= 0°), so between the start of T1’s secondary and that same 120° tap.
This can also work in reverse, to
convert three-phase to two-phase, but
in that case the load has to be perfectly
balanced, as it would be in a motor.
Wireless World System
1893 and later
In 1893, he established the foundations of what he would call in a 1900
brochure, “The Wireless World System”. It was to be a global wireless
communications and wireless power
transmission system (see Fig.13).
According to Tesla, it would allow “the
transmission of electric energy without wires” as well as point-to-point
communications.
He said that the communications
aspects of the system would allow “the
instantaneous and precise wireless
transmission of any kind of signals,
Fig.12: a
simple but
clever way
to convert
twophase AC
to threephase.
messages or characters, to all parts of
the world.” and “... an inexpensive
receiver, not bigger than a watch, will
enable him [the user] to listen anywhere, on land or sea, to a speech
delivered, or music played in some
other place, however distant”.
In 1915, in the New York Times, he
added that the system “would enable
thousands of persons to talk at once
between wireless stations and make
it possible for those talking to see one
another by wireless, regardless of the
distance separating them” (see page
136 of the PDF at siliconchip.au/link/
aby0). All that sounds very familiar
today!
To implement this system, he convinced banker John Pierpoint Morgan
(J.P. Morgan) to invest in this project,
which he built at Wardenclyffe on
Long Island, New York (more on that
next month).
Tesla received numerous patents for
wireless communications and power
transmission, such as transformer
design, transmission methods, tuning
circuits and signalling methods. Tesla
also envisaged a system of thirty telecommunications towers worldwide,
linked to telegraph and telephone
systems.
He proposed transmitting “radiations”, which were not Hertzian waves
and would apparently travel through
the Earth with little loss. The energy
of such waves could be harnessed anywhere on Earth simply by placing a
wire in the ground. We now know that
radio waves do not travel through the
Earth to any significant degree.
A reciprocating engine
1894
In 1894, Tesla received US patent
514,169 for a multipurpose reciprocating engine device that used gas or
Hand pump
The wireless light:
place a wire in the
ground that is all
G = pressure
indicator gages
Flexible spherical
envelope filled with
liquid or gas
Analogy of Tesla’s Earth Wave Vibration Theory
Each pulse of the pump is felt with equal force at all points
of he sphere
Tesla’s
wireless
power for
properlling
ships and
aeroplanes
Tesla’s Wireless Transmission Theory
The oscillating energy surges thru the Earth to every point on
the globe. Thus electric light, heat and power can be drawn
to any point of the Earth from a universal central station
Fig.13: Tesla’s proposed scheme to deliver light and power anywhere on Earth
by “ground waves” travelling through the Earth. Illustration by Tesla from
Electrical Experimenter, February 1919. Source: https://w.wiki/AZN8
18
Silicon Chip
Australia's electronics magazine
siliconchip.com.au
Fig.11: a colourised
photo of the interior of
Tesla’s East Houston St
lab. It is lit by lights of
Tesla’s design. Source:
https://teslaresearch.
jimdofree.com/
labs-in-newyork-1889-1902/
steam pressure to generate mechanical oscillatory movement to generate
electricity or for other purposes. The
development of efficient steam turbines rendered its use for electricity
generation obsolete.
In the New York World-Telegram
of July 11th, 1935, Tesla recounted
an incident of 1887 or 1888 where
he said a little version of this device
apparently brought an entire building
to resonance, potentially destroying
the building had he not stopped the
it with a hammer (www.rexresearch.
com/teslamos/tmosc.htm).
Mythbusters looked at this in their
episode on “Nikola Tesla’s Earthquake
Machine!” (season 4, episode 20 –
https://youtu.be/LHsHiKtjoag).
X-rays
1894
In 1894, Tesla worked with Crookes
tubes and a “unipolar vacuum tube”
of his own design. He noted mysterious damage to photographic plates in
his laboratory by some sort of radiant
energy.
Although X-rays had yet to be discovered or named, Tesla realised the
source of the damage was rays from the
point where the “cathodic stream” in
the devices struck the anode (Crookes
tube) or glass wall (his tube) – see
Fig.10. It was later discovered that
such a process generates X-rays.
In 1895, Wilhelm Röntgen discovered and published work about this
“new kind of rays” (X-rays). Tesla
started to work on X-rays and, in 1896,
he reported being able to produce
radiographs at a distance of ~12m; see
siliconchip.au/link/aby0 (p33).
siliconchip.com.au
Had Tesla fully recognised the phenomenon causing damage
to his photographic
plates, he may have
been credited with
their discovery. Tesla
gave Röntgen full credit
for his discovery. Later
versions of Tesla’s unipolar vacuum tube had
a cooling system.
Laboratory fire
1895
In March 1895, Tesla’s laboratory
at South Fifth Ave, New York (occupied 1892-1895) burned to the ground.
Tesla lamented, “I am in too much grief
to talk. What can I say? The work of
half my lifetime, very nearly all my
mechanical instruments and scientific apparatus, that it has taken years
to perfect, swept away in a fire that
lasted only an hour or two... Everything is gone. I must begin over again.”
This is said to have delayed his
application for radio patents.
Wireless power experiments
1895
In his East Houston Street laboratory (1895-1902), he conducted experiments on the wireless transmission of
electricity, setting up large Tesla coils,
other types of resonant transformers
and other apparatus (see Fig.11). He
was producing up to 4MV, the maximum he could safely work with in a
city building.
The Nikola Tesla Company
1895
In 1895, the Nikola Tesla Company
was set up to fund, develop, and market Tesla’s patents, which it did for the
next few decades.
Transformers/induction coils
1897
In 1897, he was granted US patent 593,138 for a safe high-voltage,
high-frequency electrical transformer/
induction coil. In this patent, he
showed single-wire electricity transmission with the return circuit flowing
through the Earth. This concept was
recently demonstrated in 2023, when
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5kW was transmitted over 5km with
87% efficiency; see https://ieeexplore.
ieee.org/document/10023995
Application for radio patents
1897
In 1897, Tesla applied for US patents
645,576 and 649,621, both granted in
1900. These are considered his first
radio patents, which he stated were
relevant to “energy of many thousands
of horsepower [being] transmitted
over vast distances”. In other words,
he thought large amounts of electrical
power could also be transmitted via
this technology.
At this stage, wireless power transmission was his main focus, rather
than radio communications.
Contrary to popular belief, Tesla did
not invent radio and, unfortunately,
did not have a good or correct understanding of the physics involved. In
1900, Guglielmo Marconi also applied
for a US patent for radio, but it and subsequent revisions were rejected based
on Tesla’s preexisting patents.
However, in 1904, Marconi was
granted US Patent 757,559 for radio,
which he had applied for in 1901.
Marconi had also previously applied
for a British patent for radio in 1896,
and it was granted in 1897, predating
Tesla. The British patent (12,039) was
the first for a system of wireless telegraphy using Hertzian waves.
Marconi was thus recognised as the
inventor of radio; he shared a Nobel
prize for it in 1909 with Karl Braun. Of
course, there were many other contributors to the invention of radio, such as
Reginald Fessenden, Heinrich Hertz,
Oliver Lodge and John Stone.
There was litigation over early radio
patents, and in 1943, the US Supreme
Court settled a case involving Tesla’s
patents. However, it was not, as is often
claimed, a case about who invented
radio but who would be compensated
by the US Government for using various patents during WW1. The story
is too complicated to go into here; see
https://earlyradiohistory.us/tesla.htm
Next month
In the following article, we’ll pick
up where we left off and cover the
remainder of Tesla’s life, from 1898
until his passing in 1943. We’ll then
go over related topics such as Tesla’s
mistakes and misconceptions, why the
World Wireless System could never
work, the ‘war of the currents’ and
Tesla’s lost files.
SC
October 2024 19
3D Printer
Filament
Drying Chamber
This enclosure can store up to four 1kg reels of 3D printer filament, keeping them dry
and ready for use at any time. You don’t even need to remove them – the filament can
simply be fed to the printer through a small hole in its lid!
Part 1 by Phil Prosser
T
he ability to produce functional 3D
parts, either standalone or as part
of a larger project, is incredibly useful. Over the last few years, 3D printer
prices have fallen remarkably. You can
now find some amazingly-priced 3D
filament printers on the market.
The major Australian electronics
stores (Jaycar and Altronics) both stock
“Creality” products, which I think are
excellent. There are plenty of other
good alternatives available online.
My grandson, who wanted to buy
printed parts, drew me into this. I
pointed out that for the price of a
handful of ‘bought bits’, we could
buy our own 3D printer. So I did. I
quickly found that being able to manufacture complex 3D parts was incredibly handy.
Like most of these technical things,
once you start, there is an amazing
range of extras you might want or
need. One surprising accessory is a
filament dryer. It had not dawned on
me that plastic filament can absorb
moisture. However, PLA (polylactic
Photo 1: the surface of the black boat
is not smooth due to moisture in the
filament. The white filament was dry,
giving a much better result.
20
Silicon Chip
acid), probably the most common filament these days, is sufficiently hygroscopic that moisture can become a real
problem.
3D printers work by heating the
plastic filament to around 200°C (or
much hotter for materials like ABS)
and extruding it through a small nozzle, typically 0.4mm in diameter.
The printer acts like an X-Y plotter
and deposits lines of melted filament
where required, in layers, thus building the part.
It is incredible to consider that a
large print may have the printer laying down material in this manner for
12-24 hours, all without error.
If that sounds too complicated to be
reliable, well, you need to get many
things right for the printer to work
well. However, when set up correctly,
reliable results can be achieved. I
would say that most electronics hobbyists would have the inclination, skill
and inquisitiveness to learn the tricks
and tips required to keep a 3D printer
running, but they certainly are not ‘set
and forget’.
When I first ran the printer, things
went swimmingly well. However, I
later realised that even a little moisture in the filament can cause problems when it is heated in the extruder.
The moisture boils into steam, which
pushes filament out of the extruder and
causes ‘blobs’ on the print.
Photo 1 tries to show the difference
between fresh new filament (white)
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and some that had been lying around
(black).
All the printer knows is that it has
driven the correct length of filament at
the right time, but the ‘blobs’ mean it
doesn’t end up exactly where it should
be. So surfaces can get ‘blobby’, and
you hear small popping noises during
printing.
While PLA certainly suffers from
these problems, other materials, such
as Nylon, also have a terrible reputation for being hygroscopic and hard
to print with.
While the printers themselves are
competitively priced, I was not really
into spending hundreds more on a
fancy filament dryer. Some people
use a food dehydrator, which, while
cheap, does not handle multiple reels
or allow you to feed straight from the
dryer to your printer.
I was convinced that I could easily
make something to do the job with a
handful of bits from the spares box,
a leftover laptop power supply and
maybe a microcontroller. We can even
customise the size and shape to suit
our workspace and needs. So, while
we provide a complete parts list here,
you can modify the design to reuse bits
you already have, saving a few bucks.
There does not seem to be a specific
‘right way’ to dry or, perhaps more
correctly, dehydrate filament. All
approaches use an elevated temperature and some form of timer. Some add
air circulation, while a few incorporate
siliconchip.com.au
a mechanism to change the air in the
box periodically.
The idea of heating the filament in a
sealed enclosure is that when the air in
the enclosure gets hotter, it can hold a
lot more moisture, so relatively speaking, the air is dryer. In other words, the
relative humidity of the air in the box
reduces as it is heated.
Fig.1 shows that for a typical room
at 20°C and 40% relative humidity
(RH), there is about 6g of water per
kilogram of air. If the box is sealed,
there is always the same amount of
water in the box. So, at 42°C, we see
the relative humidity will be about
10%. Because the air is now quite dry
(for its temperature), it pulls moisture
from everything in the box.
PLA filament that has absorbed
moisture does not dry out quickly; drying times are typically 6-9 hours. By
keeping the dryer sealed and including some desiccant, such as silica gel,
in the enclosure, we can keep the filament dry and ready for use. If you will
not use the dry filament for a while,
it remains a good idea to seal it in a
vacuum bag.
and substantial protection circuitry.
The second part is making an enclosure for the filament. There are several
possible approaches, ranging from
very simple to quite complicated.
Choosing your approach to the container is probably the most critical
choice, as the controller is not that
complicated.
We built two enclosures. The first
was a custom one optimised for our
needs and just a little bit fancy – see
Photo 2 and the image above. The
second was an 18L plastic tub into
which we installed the controller and
heater (Photo 3). The latter proved to
be quick and simple to assemble and
quite effective. It must be said that it
looks a lot like a plastic tub, though.
We will provide an overview of how
to build the custom enclosure but will
not go into great detail. If you are not
confident in filling in the details yourself, stick to using the off-the-shelf
plastic tub.
Both enclosures use the exact same
controller, but we have arranged the
heating plates quite differently to suit
the differing enclosure shapes. In both
cases, we found that without adding
insulation to the enclosure walls, we
could achieve about 47°C inside with
50W of heating.
Adding a layer of Corflute to the
bottom and walls of the enclosures
increased the temperature at that
power level by well over 5°C, effectively reducing the amount of power
needed to keep the enclosure at a given
temperature.
The unit is powered by either a 24V
DC 4A plugpack or an 18-24V 3A+
DC laptop power supply. Is it just
me who has a growing collection of
these things, which seem to outlast
the laptops they powered? Either way,
it drives a resistive heater in the box
via a control board, much of which is
safety circuitry.
We put a couple of small bags of
silica gel in the box to absorb any
The design
This project has two distinct parts.
The first is a filament dryer controller
board. This is a standalone thermostat
controller board that could equally be
used to control an incubator or curing
oven for painted parts. The board is
essentially a thermostat with a timer
siliconchip.com.au
Fig.1: water in the air plotted against temperature for a range of different
relative humidity (RH) values, from 10% to 90%. You can see how hotter air can
contain a lot more moisture for the same RH figure.
Australia's electronics magazine
October 2024 21
moisture released by the filament and
occasionally change the air in the box
to expel excess moisture. Cat litter
crystals are simply silica gel, so for
$10 at the local supermarket, we got
a huge bag of silica gel from which
we make our own drying sachets. We
just put it in paper envelopes to pop
in the dryer.
Our filament dryer hangs the reels
on a rod and allows you to draw the
filament straight from inside the dryer
box.
We decided to omit a fancy display,
which technically is not hard but adds
construction constraints and cost.
During development, we noted that
even with a fan circulating air in the
dryer, the temperature throughout the
box varied significantly. So, a temperature display may feel important, but it
would only be indicative. Leaving out
the display also avoids the need for a
humidity sensor.
This decision was hard but it keeps
things simple and cheap. If the box is
warm and you have fresh silica gel,
after a couple of cycles, your filament
will be as dry as it will get. Some really
cheap humidity sensors are available
online that you can pop in the box if
you want to monitor it.
Because we are making potentially
combustible materials hot, we have
taken a very conservative approach to
the design to ensure that it is as safe as
reasonably possible. Refer to the text
box on safety analysis for a discussion
of how key design drivers were arrived
at. If you are designing your own enclosure, you should consider the hazards
we list and satisfy yourself that your
approach mitigates all hazards.
The design presented here is mostly
about implementing the control and
safety systems identified in Table 1,
which mandate the following inclusions:
• A controller that maintains the
Dryer in a safe state until the user
deliberately starts a cycle.
• A thermostat, allowing the temperature to be set from room temperature to 50°C.
• A timer that allows a six- or ninehour drying period, then shuts the
heater down.
Table 1 – Hazard & Risk Assessment
Hazard
Initial Risk
Mitigation
Final risk
High
Implement a temperature control system.
Limit the maximum energy available so the
ultimate temperature without control is safe
(50W gives a maximum of around 60°C).
Low
Short circuit or critical
component failure
Low
Integrate thermal switches/fuses that disable
the system at a safe temperature. Include
a fuse in the design, to blow in case of a
catastrophic short.
Low
Excessive heating since the
control system does not
sense the real temperature
Moderate
Include a fan to circulate air throughout the
enclosure.
Low
Failure of fan results in loss
of thermal control
Low
Integrate a ‘fan operating’ sensor and shut the
heater down if the fan fails.
Low
Heating element contacts
personnel
Medium
Mount heating resistors inside a plenum
or behind sheet aluminium to minimise the
likelihood of contact with personnel.
Low
Personal
injury
User touches energised part
Medium
Operate the dryer from an isolated plugpack
with a low voltage output.
Low
Electric Shock
Long-term heating results in
auto-ignition of material
Low
A timer shuts the unit down after six or nine
hours
Low
Fire and
uncontrolled
energy
Enclosure operates
unexpectedly
Medium
The system starts in an idle state. Force the
user to press a start button to commence
drying.
Low
Inadvertent
operation
Software fails
Low
Critical controls (thermal- and energy-related)
are to be implemented in hardware.
Low
Inadvertent
operation
Heating element touching
combustible material
Medium
Limit the heating power such that the element
does not exceed 80°C. Mount the heating
element so it is not in permanent contact
with timber. Use polypropylene Corflute
for insulation, which has an autoignition
temperature of 288°C (flash point 260°C).
Low
Fire
Misuse – user fills the
enclosure with rags or paper
Medium
Integrate thermal cutout on heater plates at
90°C (high but safe).
Low
Fire
Misuse – user covers the
dryer with a blanket
Medium
Use a thermostat to control the internal
temperature, with a safety shutdown & timer.
Low
Fire
Uncontrolled heating,
causing the enclosure to
become excessively hot
22
Silicon Chip
Australia's electronics magazine
Consequence if
not mitigated
Damage or
combustion
of filament or
enclosure
siliconchip.com.au
• Onboard fusing.
• A thermal cutout on each heater
element.
• A thermal fuse on the controller board.
• The maximum heating power is
limited to 50W.
• A ventilation fan that is integral
to the controller board, ensuring airflow in the box.
• An interlock that shuts down
the heater if the ventilation fan
stops.
We have spread the heating across
six 25W resistors, which dissipate 8W
each into the large aluminium heating element. Even if everything fails,
they will never get hot enough to create a hazard. We tested our two boxes
with all controls disabled and determined that 50W of heating resulted
in a maximum box temperature of no
more than 60°C.
Looking at what is on the market and
having read a lot of tests on commercial filament dryers, most make wild
claims as to the temperatures they
achieve. We feel that 50-55°C is a good,
safe temperature. If you want it to get
hotter, you would need to increase
the power or reduce the size of the
box. The controller will accommodate
that, but we advise you approach any
changes with appropriate caution.
You may have your own spin on
how to build this; you could design
a box that better suits your needs
and use a surplus power supply.
You could even reuse some different heating resistors. That will let you
build a dryer for a fraction of the cost
of a ‘bought one’, but make sure you
follow our safety tips so everything
goes well for you.
We will first describe the controller and then present a couple of way
it can be used.
Photo 2: this DIY
timber box can be sized
to suit your needs. It has a rod
for hanging the reels and convenient
handles. The lid is removable and has a hole
for feeding filament through.
The controller
The controller can operate from
18-24V DC, so you can recycle a laptop supply or similar power brick. It
must deliver sufficient current for your
resistor bank. The input is fused; select
a fuse rating an amp or so above your
expected maximum operating current.
There is also a polarity protection
diode that will dissipate about 2W;
we have included heatsinking fills on
the PCB, and this ‘extra power’ simply adds to the overall heating in the
system.
The controller is expected to be
siliconchip.com.au
Photo 3: this box
from Bunnings
doesn’t look as elegant
and may be a little large
for some people, but it’s
much less work to prepare
and does the job well.
Australia's electronics magazine
October 2024 23
installed inside the Filament Dryer,
as that simplifies the wiring, and the
temperature sensor is on the board.
This means the controller will be
operating at up to 50°C, perhaps a little more. That fine for most electronic
components, but you will notice that
we have specified high-temperature
electrolytic capacitors and allowed for
heatsinks on transistors Q1 and Q2.
Circuit details
The circuit is shown in Fig.2. An
8-bit PIC16F15214 operates as the
timer, while an LM336-2.5 voltage
reference (REF2) is used to produce a
2.5V reference, which is buffered by
half of an LM358 op amp (IC1a). This is
used in the temperature measurement
circuit. The reason we have chosen the
LM336-2.5 is it produces a reference
voltage that is very stable over a wide
temperature range.
The LM336-2.5 has a variation of
just 6mV over 0-70°C, so we can expect
to see an error of less than a degree in
temperature control over our operational range.
The temperature sensor itself is a
simple 1N4148 silicon diode (D6),
using its -2.1mV/°C temperature coefficient. This is stable, reliable and used
in many measurement circuits. The
controller is a ‘Bang-Bang’ style, which
simply turns the heating element on
and off rather than implementing
fancy control loops. This choice is
again to keep things simple and cheap.
The controller comprises half of
the LM358 (IC1b), which compares
the voltage across the sense diode to
the temperature set voltage. We use
the 2.5V reference voltage to set the
current through the sense diode via
a 4.7kW resistor. The same reference
Fig.2: the circuit of the Filament Dryer Controller. REF2 and IC1a create a 2.5V reference (trimmed
by VR1). This biases diode D6, the temperature sensor. The voltage across D6 and the setpoint from
VR2/VR3 are compared by op amp IC1b to drive Mosfet Q2 for powering the heating elements. Microcontroller IC3’s timer
limits the heating time and powers the fresh air fan periodically.
24
Silicon Chip
Australia's electronics magazine
siliconchip.com.au
voltage generates the set voltage using
trimpots VR1 and VR2 plus a couple
of padder resistors.
By using this very stable 2.5V reference, we can be assured that the current through the sense diode and the
set voltage are constant over time and
temperature.
At room temperature, there is 400μA
flowing through the sense diode, giving 0.56V across it. With the 12kW and
2.7kW padders and two 500W potentiometers, we get a temperature set point
range of about 20-50°C. The reason we
have included two pots is to allow us
to use one (VR2) to set the minimum
temperature to room temperature,
while the other (VR3) is used to choose
the temperature setpoint.
With trimpot VR2 at the nominal
value of 220W, the minimum voltage will be 0.489V (2.5V × 2.90kW
÷ [12kW + 2.92kW]). The maximum
voltage will be 0.554V (2.5 × 3.42kW
÷ [18kW + 3.42kW]). The difference is
0.065V, and at 2.1mV/°C, that gives a
spread of 31°C.
Even using 1% resistors, the errors
in the voltage divider are significant.
If one is 1% high and the other is 1%
low, the setpoint could move as much
as 7°C. By adjusting VR2 so the minimum setpoint is room temperature, we
can calibrate such errors out.
The output of IC1b is low when the
sensed temperature is below the setpoint and goes high when the temperature exceeds the setpoint. The 8.2MW
resistor adds about 2°C of hysteresis
by feeding back the output voltage to
slightly shift the setpoint voltage.
The ratio of the 8.2MW and 4.7kW
resistors results in a shift of just a couple of milivolts, which is what we
need. This stops IC1b from oscillating
once the setpoint is reached.
With the controller being flat out on
or off, and the degree or two of hysteresis, the temperature control is not
super precise. But for warming the filament to dry it out, that is OK.
For the timer, we started by considering simple CMOS timer circuits and
the venerable 555. To get a nine-hour
period from these is not easy, so the
cheapest way to make the timer was
to use a PIC. These cost nearly $1.50
in single units, a fraction of the cost of
the discrete solution, and can be programmed to do a huge range of jobs.
We consider the timer to be an integral part of this design and strongly
recommend against omitting it.
Parts List – Filament Drying Chamber
siliconchip.com.au
Australia's electronics magazine
1 double-sided PCB coded 28110241, 126 × 93mm
1 18-24V DC 3A+ power supply (eg, laptop charger)
2 12V DC 40mm fans, 10mm-thick [Altronics F0010A]
1 40mm fan grille [Altronics F0012]
2 PCB-mounting M205 fuse clips (for F1)
1 5A 250V M205 fuse (F1)
1 77°C axial thermal fuse (F2) [Altronics S5631]
5 2-pin vertical polarised headers, 2.54mm pitch (CON1-2, CON4-5, CON7) [Altronics P5492]
5 2-pin polarised header plugs with pins [Altronics P5472 + 2 × P5470A each]
1 5-pin header, 2.54mm pitch (CON6; optional, for programming IC3 in-circuit)
1 PCB-mounting DC socket, 2.1mm ID or to suit power supply plug (CON8)
1 PCB-mounting 90° miniature SPDT toggle switch (S1) [Altronics S1320]
1 PCB-mounting 90° sub-miniature SPST pushbutton switch (S2) [Altronics S1498]
1 10kW side-adjust single-turn trimpot (VR1)
1 500W side-adjust single-turn trimpot (VR2)
1 500W 16mm single-gang linear potentiometer (VR3)
2 TO-220 micro-U heatsinks (optional) [Altronics H0627]
2 90°C normally-closed (NC) thermal switches/breakers (S3, S4) [Altronics S5612]
Hardware (common to both versions)
1 3D-printed vent (“Vent Rotor.STL”, “Vent Rotor Base.STL” & “Vent No Fan.STL”)
1 3D-printed fan cover (“Fan Shroud.STL”)
6 M3 × 25mm panhead machine screws
18 M3 hex nuts & 32 M3 flat washers
1 3m length of high-temperature (90°C+) heavy-duty hookup wire
1 250mm length of 6mm diameter heatshrink tubing
1 2m length of 5-10mm wide open-cell foam adhesive tape
1 small tube of thermal paste
Hardware (for plastic box version)
1 polypropylene box [Bunnings 0171464]
2 1.5mm-thick aluminium plates, 210 × 180mm
Panhead machine screws: 8 M3 × 6mm, 32 M3 × 10mm, 8 M3 × 16mm, 6 M3 × 25mm
Tapped spacers: 4 M3 × 15mm, 16 M3 × 25mm male/female hex spacers [Altronics H1243]
Other: 58 M3 shakeproof washers, 46 M3 hex nuts
Hardware (for timber box version)
2 3D-printed handles (“Filament Dryer Rail Tall.STL”)
1 sheet of 12mm MDF or plywood
1 1.5mm-thick aluminium plate, 330 × 225mm
Panhead machine screws: 6 M3 × 6mm (30 if building lid), 16 M3 × 10mm, 4 M3 × 16mm,
24 M3 × 25mm, 1 M4 × 10mm (for attaching handle to lid)
Tapped spacers: 12 M3 × 6mm (for lid), 10 M3 × 15mm
Other: 42 M3 shakeproof washers, 38 M3 hex nuts
Capacitors
1 470μF 35V 105°C electrolytic [Altronics R4865]
2 10μF 50V 105°C electrolytic [Altronics R4767]
7 100nF 50V multi-layer ceramic or MKT
Semiconductors
1 LM358 dual single-supply op amp, DIP-8 (IC1)
1 LM336BZ-2.5 voltage reference diode, TO-92 (REF2) [Altronics Z0557]
1 PIC16F15214-I/P 8-bit microcontroller programmed with 2811024A.HEX, DIP-8 (IC3)
1 LM317T adjustable positive linear regulator, TO-220 (REG1)
1 BD139 80V 1.5A NPN transistor, TO-126 (Q1)
1 IRF540(N) 100V 30A N-channel Mosfet or similar, TO-220 (Q2)
2 BC548 30V 100mA NPN transistors, TO-92 (Q3, Q4)
1 BC338 25V 800mA NPN transistor, TO-92 (Q5)
1 BC558 30V 100mA PNP transistor, TO-92 (Q6)
4 1N4004 400V 1A diodes (D1, D3, D11, D13)
1 R250H or 6A10 400V 6A diode (D2) [Altronics Z0120A]
3 1N4148 75V 200mA diodes (D4-D6)
1 12V 0.4W or 1W zener diode (ZD10)
2 5mm red LEDs (LED7, LED8)
1 5mm green LED (LED12)
Resistors (all ¼W 1% axial unless noted)
1 8.2MW
1 100kW
1 12kW
12 4.7kW
1 2.7kW
3 1kW
1 330W
1 47W
6 39W (18V), 47W (19-20V) or 68W (24V) 25W aluminium body resistors [Ohmite HS25 series]
October 2024 25
Our dryer includes two fans. The
first is to circulate air inside the box
and it runs full-time. There is also a
ventilation fan that runs briefly every
10 minutes. This is intended to draw
fresh air into the box and to exhaust
the hot (and possibly moist) air. This
ventilation fan is driven by the PIC
microcontroller.
We do not want to continuously
change the air in the enclosure, as it
would require a lot of power to keep
the temperature elevated. So our tiny
PIC microcontroller drives the vent
fan sparingly.
Software
The program in the timer is quite
simple. At power-up, the PIC goes into
an idle state, disabling the heater and
ventilation. It stays in this state until
the user presses the start button. This
requires a deliberate action by the user.
Once the start button is pressed, the
timer moves into the running state. If
IC3’s RA4 digital input is low, the timer
drives its RA2 output low and counts
nine hours. If RA5 is low instead, the
output is low for six hours. After the
selected time, the heater is switched
off and the system goes back to the
26
Silicon Chip
idle state. If the input is invalid, it
remains idle.
The PIC includes a secondary
timer that drives digital output RA1
to switch on the ventilation fan every
10 minutes.
The timer output and the output of
the temperature sensor comparator
are combined using open-collector
transistors Q3 and Q4, which disable
heater drive transistor Q2 when they
are on. When the box is up to temperature, the output of IC1b goes high,
switching on Q3, which disables the
heater. Green LED12 is in series with
this output, and lights showing that
the set temperature has been achieved.
Switching the load on is implemented using an IRF540 or similar power Mosfet with a gate pullup
resistor to 12V. The gate drive pullup
is derived from the ventilation fan
power supply, which might seem an
odd choice. The ventilation fan draws
current through D11, D13 and the parallel 47W resistor.
The specified fan draws 60mA in
operation and develops 1.2V across
these diodes. This voltage switches on
Q6 on via its 4.7kW base resistor, which
forms the Mosfet gate drive.
If the fan stalls, its internal controller reduces its supply current to
2mA and attempts to restart it every
few seconds. This 2mA current only
generates 94mV across the 47W resistor, which is not enough to switch Q6
on, and consequently the Mosfet gate
drive is removed. Thus, we disable the
heater if the ventilation fan is stalled
or not working.
For Q2, pretty much any TO-220
package, low-RDS(ON) N-channel Mosfet will work. They virtually all have
the same pinout. If you want to use
a different Mosfet from our recommended part, look for one with an
RDS(ON) under 0.1W.
For example, the MTP3055V has an
RDS(ON) of 0.18W and for a load current of 3A, it will dissipate 1.6W (3A2
× 0.18W). That would demand the use
of a flag heatsink; there is room for this
on the PCB. The recommended IRF540
has an RDS(ON) of 0.077W and will
dissipate 0.7W at 3A (or 0.4W for the
IRF540N version), which will make it
warm but it won’t require a heatsink.
Photo 4: the top side of the prototype PCB. The fan is mounted to the underside
using four M3 x 16mm machine screws with matching hex nuts.
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There are two headers for wiring up
the heater resistors. This allows you
to run separate wiring to two banks of
resistors, making the wiring and layout easier in some builds. The current
rating of the recommended Altronics
P5492 headers is 3A, so you could get
away with using just one.
We have included a thermal fuse in
the power supply to the Mosfet. The
specified fuse has a current rating of
10A AC but in our application, we are
breaking nominally 2A DC. The fuse
does not have a DC rating but that is
well within its capacity. This device
will fuse at 77°C, and will hold at 55°C
continuously. Should your enclosure
exceed 55°C for extended periods, you
may trigger this protection.
The heater
We performed a number of tests on
the boxes we’re presenting and determined that we need 50W to heat our
enclosures to 50°C reliably in a 20°C
room. This is also a good maximum,
as per the safety considerations we
touched on earlier.
To allow us to spread the power
around the enclosure, we are using
six 25W resistors mounted to large
heatsinks. We have used 68W devices,
which at 24V will dissipate 50W in
total. To spread the heat, we used a 330
× 225mm aluminium sheet folded to
fit inside our timber box, or two 210
× 180mm panels for the plastic box.
If using a 19V supply, the heating
resistor values need to be reduced to
47W to keep that 50W target.
We recommend the cheapest aluminium case power resistor we could
find, mentioned in the parts list. The
cost is around $20 for six, so you
can save some decent money reusing
parts you have. It is important that the
devices you select can be bolted to the
heat spreader, as this ensures they do
not get hot enough to create a hazard.
We tried using 10W ceramic resistors each dissipating 5W. While they
were operating within their specification, their surface temperature of over
130°C would have the potential to create a hazard if combustible material
fell onto them.
Safety considerations for the Filament Dryer
In designing the controller, we undertook a hazard assessment and developed controls for each hazard we identified, seeking to mitigate these hazards as much as
reasonably practicable. This in broader engineering often forms part of a “Safety
Engineering Program”. This process involves identifying credible hazards them
applying the ‘hierarchy of controls’ which, in order, are:
● Eliminate the hazard
● Substitute to avoid / minimise the hazard
● Apply engineering controls
● Add administrative controls (how it is used)
● Use Personal Protective Equipment (PPE)
In safety engineering, there is an important differentiation between a hazard,
which is a potential outcome, and the risk this represents, which considers the
likelihood of this occurring. The intention of applying the hierarchy of controls is
to mitigate and minimise the overall risk of a system.
Our hazard assessment was undertaken to inform the design of the project and
to shape the solution, both to minimise the underlying hazards in the design and
also to apply substitutions, engineering and administrative controls to further mitigate residual risks. By keeping a record of the approaches to managing safety, and
building those into the design, we can then test the project to ensure that these
controls do what we expect.
The hazards and controls we identified for the filament dryer are shown in Table
1 (Hazard & Risk Assessment). Some significant changes in design were implemented. Those practised in the safety art will note that we have picked parts of a
larger process to document here, as a full safety program is comprehensive and at
times less than fascinating. We have, however, included some important elements
for your consideration when making your own version of this.
Next month
The second and final article next
month will have the construction
and testing details, including building or adapting and then insulating
the container.
SC
Photo 5: the Filament
Dryer in use, showing
how filament is drawn from the container.
siliconchip.com.au
Australia's electronics magazine
October 2024 27
The MIPI I3C Bus
There is a brand-new serial bus on the block named I3C (Improved InterIntegrated Circuit). It is beginning to appear in mainstream parts; here’s what
you need to know about it.
By Andrew Levido
R
ight now, if you want to connect
a peripheral like a sensor or an
EEPROM to a microcontroller, you
would probably use either the SPI
(Serial Peripheral Interface) or I2C
(Inter-Integrated Circuit) bus. These
are tried and tested serial interfaces
that date back to the 1980s.
The new I3C standard was developed by the MIPI Alliance (www.mipi.
org) and incorporates key attributes of
the venerable I2C and SPI interfaces, as
well as some interesting new features
such as dynamic addressing, in-band
interrupts, high data rate modes and
28
Silicon Chip
hot-join capability. As the name suggests, I3C is closely aligned with I2C.
In fact, I2C devices can even be used
on an I3C bus.
Like SPI and I2C, I3C uses a controller, typically a peripheral within
a microcontroller, and one or more
targets. Fig.1 shows a comparison
between an I2C, SPI and I3C bus, each
connecting a controller (master) with
three targets (slaves) that can each
interrupt the controller. With I2C,
the targets are addressed via the bus,
whilst SPI requires a separate chip
select (CS) signal for each target.
I2C uses bidirectional data transfer on the data line (SDA), while SPI
requires two unidirectional lines
(MISO and MOSI) for bidirectional
communication. Both require separate
interrupt lines if targets are to interrupt
the processor asynchronously.
I3C uses device addressing and
bidirectional data transfers, just like
I2C, but does not require dedicated
interrupt signals, since targets can
send interrupts to the controller via
the bus.
The best of both worlds
Fig.1: compared with I2C and SPI, I3C requires fewer
data lines for bidirectional communication with interrupt
capability. Data throughput is similar to SPI, while
addressing is managed over the bus.
The I2C protocol uses open-drain
drivers to achieve bidirectional signalling on the clock and data lines.
High-to-low transitions are actively
driven, but low-to-high transitions rely
on pull-up resistors, so the signal rise
time is limited by the resistor value
and bus capacitance.
The maximum data rate that can
be achieved over I2C is therefore significantly lower than SPI, where the
bus is actively driven high and low by
push-pull drivers.
For I2C, the maximum clock speed
is typically 400kHz, or 1MHz with
Fast mode+ drivers. There is a standard allowing speeds up to 3.4MHz,
but it is not widely supported. The
SPI interface does not have standard
clock rates but can typically operate at a maximum clock speed of
10-20MHz.
I3C uses drivers that can operate in
open-drain mode when required, but
they switch to push-pull mode whenever possible to maximise the data
transfer rate. External pull-ups are not
required – these are provided by the
controller when necessary.
Besides using open-drain drivers
when communicating with legacy I2C
devices, open-drain drivers are used
whenever bus arbitration is required;
we’ll cover that in more detail later.
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Data transfers generally use the pushpull drivers.
As a result, the I3C bus operates
at a range of clock speeds. In pushpull mode, the maximum clock speed
is 12.5MHz, while in open-drain
mode, it is 2.5MHz. The clock speed
drops to 400kHz (or 1MHz for Fm+)
when communicating with legacy
I2C devices.
Address arbitration
All communications on the I3C bus
begin with the bus in the idle state,
where the SDA and SCL lines are
both high, and with open-drain drivers enabled.
The start of a transaction is indicated by a start condition, a highto-low transition on SDA while SCL
remains high. A transaction is terminated with a stop condition, a low-tohigh transition on SDA with SCL high.
All other SDA transitions occur with
SCL low. Repeated start conditions
may be issued to allow multiple messages per transaction. A target address
header follows each start or repeated
start condition.
If all this sounds familiar, that’s
because, so far, this is identical to how
I2C works. One key difference is that,
with I3C, it is possible for targets to
issue a start condition and/or to emit
the address header under certain circumstances. On an I2C bus, only the
controller can do that.
This can happen when a target
wishes to signal an interrupt to the
controller, a device wants to ‘hot join’
the bus, or a target wishes to become
the controller. It is therefore possible
that two or more devices may try to
write the address header to the bus at
the same time. We need a mechanism
to arbitrate this conflict.
The open-drain nature of the bus
during this phase provides a form of
Fig.2: address arbitration occurs if two devices simultaneously attempt to
write an address header to the bus. On the fourth clock cycle, device A’s
zero overrules device B’s one; device B recognises this and gives up. Because
zero-bits are asserted actively on the bus, while ones are passive, the device
with the lowest address always wins arbitration.
natural arbitration, ensuring that the
device with the lowest address always
‘wins’. Consider the example shown
in Fig.2. Here, devices A and B, with
hexadecimal addresses 0x26 (binary
010 0110) and 0x29 (binary 010 1001),
respectively, attempt to write their
address headers (7-bit address + read/
write bit) to the bus.
On the first clock cycle after the start
condition, each emits a logic zero by
pulling the bus down with their opendrain driver. Both A and B monitor the
bus and check that its level matches
the value they emitted. If so, they each
continue to deliver the header.
Both devices emit a logic one on
the second clock cycle, and the passive pull-up pulls the bus high. Again,
each device sees that the bus state is as
expected and moves on to the next bit.
This process continues until the 4th
bit, when device A emits a zero and
device B emits a one. The bus will be
pulled low by device A’s open-drain
driver, so device B will see a mismatch
between the logic level it emitted and
that which appeared on the bus. At this
point, device B has ‘lost’ the arbitration and ceases to participate.
Meanwhile, device A continues to
place its address on the bus unopposed, and the transaction it initiated
ensues. Under these circumstances,
device B will likely reattempt to assert
the header after the transaction concludes and the bus is idle once again.
This type of arbitration is zero-
dominant, so the device with the
lowest address always wins. For this
reason, most controller-initiated I3C
transactions don’t begin with a target
address header as they do in I2C. If
they did, it would not be possible for
the target with the highest address to
win an arbitration.
Fig.3: controller-initiated read
or write transactions on the
I3C bus look similar to their
I2C counterparts. However, I3C
transactions generally begin with
the special address 0x7E, allowing
targets to assert their addresses
if necessary. Each data byte is
followed by a T-bit rather than an ...
... acknowledge bit; it is a parity bit
for writes and a continuation bit for
reads.
siliconchip.com.au
Australia's electronics magazine
October 2024 29
Instead, they generally begin with
the special address 7E hexadecimal
(111 1110 binary). This address is
higher than any valid target address,
so it is guaranteed to lose arbitration
to any target, should there be a conflict.
sending data bytes, depending on the
value of the read/write bit.
Because the sender is in pushpull mode, it is not possible for the
receiving device to ACK each byte,
as happens in I2C. Instead, the sending device sends a ‘T-bit’ on the 9th
clock cycle.
Single data rate transactions
For writes, the T-bit sent by the conI3C supports several different trans- troller is a parity bit protecting the preaction types. Let’s first look at a sim- ceding byte. Odd parity is used; The
ple example where an I3C controller parity bit is set or cleared such that the
wishes to write to or read from a tar- total number of ones in the data and
get, as illustrated at the top and centre the parity bit is odd.
of Fig.3, respectively.
In the case of reads, the target sets
SDR transactions begin from the the T-bit to indicate that more bytes of
idle state, with the controller issu- data will come. The last byte has its
ing a start condition followed by an T-bit cleared.
address header containing the special
Fig.3 also shows a typical hybrid
7-bit address 0x7E and a write (zero) write-read that might be used to
bit. All I3C targets will acknowledge address and then read a specific reg(ACK) this address by pulling SDA low ister in a target. The arbitrable 0x7E
on the 9th clock cycle.
header is written as before, followed
The controller then emits a repeated by a repeated start condition and a
start condition followed by a non- write of the register address to the tararbitrable address header containing get. Another repeated start condition
the target’s dynamic address, along is then issued, followed by a read to
with the read or write bit, depend- obtain the register value; in this case,
ing on the desired data direction. a single byte.
The target with a matching dynamic
Apart from the T-bit replacing the
address will acknowledge (ACK), and acknowledge bit, and the clock speed,
any others will ignore the rest of the this is all very similar to I2C.
transaction.
Apart from this ACK, the whole In-band interrupts
transaction following the repeated
One elegant feature of I3C is the
start is carried out in push-pull mode in-band interrupt (IBI) capability. A
with a nominal 12.5MHz clock. The target may signal an interrupt by placcontroller or the target then begins ing its dynamic address (and the read/
write bit set to one) on the bus following a start condition. It may do this
when the controller or another target
initiates a start condition, or it may
emit the start condition itself.
Since a controller message generally begins with the 0x7E address, the
interrupting target will win the arbitration. If two or more targets interrupt
simultaneously, the lowest addressed
one will win. Fig.4 shows the typical
IBI process.
The controller may accept the interrupt by ACKing the request as shown
at the top or decline it by NACKing it
as shown below that.
If the controller accepts the interrupt, it reads in a “mandatory byte”
(MDB) sent by the interrupting target
with details of the interrupt source.
The target may optionally send additional bytes of data, indicated by the
value of the T-bit. Once finished, the
controller terminates the transaction
with a stop condition.
If the controller denies the IBI
request, the target may continue to
try interrupting until the controller
accepts. The controller may prevent a
target from interrupting by sending a
specific command to the target.
Common command codes
This introduces another feature of
the I3C standard – the ability to send
predefined common command codes
(CCC) to targets. All targets must support a subset of CCCs, but others are
Fig.4: a target may signal an In-band
Interrupt (IBI) by asserting its address
header after a start condition. The
controller accepts or rejects the IBI
request by ACKing or NACKing the
address. If accepted, the controller
reads a Mandatory Byte describing
the interrupt reason; the target may
send further data after that.
Fig.5: common command codes
(CCCs) allow the controller to put
targets in defined states (eg, by
turning IBI on or off) or to query the
target (eg, to get device ...
... characteristics). Some CCCs are broadcast to all targets on the
bus, while others are directed to one or more specific devices.
30
Silicon Chip
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optional or only required when the
target has specific features.
All CCCs are one byte long, with
those in the range 0x00 to 0x7F being
broadcast codes that all devices will
respond to, and those in the range 0x80
to 0xFF being direct codes intended
for only a specific target. The standard defines many CCCs, a selection
of which are included in Table 1.
Fig.5 shows how broadcast or
direct CCCs are used. Broadcast CCC
transmissions begin with the special
address 0x7E, followed by the command code and any associated data
bytes.
Direct CCCs begin the same way,
with a 0x7E address followed by the
CCC. This time, there may be a ‘defining byte’ associated with the CCC. A
repeated start condition is then issued,
followed by the dynamic address of the
target to which the CCC is directed,
plus a read/write bit. Additional targets may be addressed by issuing
another repeated start condition and
target address header.
Dynamic addressing
So far, we have referred to target
addresses as though they are fixed,
like I2C device addresses. In I3C, the
controller must assign each target
a 7-bit dynamic address before any
directed transactions can occur. The
target retains this address until it is
reset or the target receives a Reset
Dynamic Address Assignment (RSTDAA) CCC.
Dynamic addressing has a couple
of advantages over fixed addressing.
Firstly, since lower addresses have
higher arbitration priority, the controller can assign interrupt priorities by
appropriate dynamic address choices.
Secondly, it avoids conflicts between
devices with identical static addresses,
as occurs with I2C.
That it can happen is unsurprising
since there are only about 120 non-
reserved 7-bit addresses and many
thousands of unique devices. For
example, the site https://i2cdevices.
org/addresses suggests the address
0x44 is shared by no fewer than 19
devices, ranging from an IR temperature sensor to a high-side current monitor to a resistive touchscreen controller. Dynamic addressing avoids such
overlaps.
Table 1 – some of the more frequently used I3C Common Control Codes
CCC
Type
ENEC
Enable Events Command
Broadcast Write 0x00
Direct Write 0x80
Enable Target events such as Hot-Join and In-Band Interrupt
RSTDAA
Reset Dynamic Address
Assignment
Broadcast Write 0x06
Direct Write 0x86
Discard current Dynamic Address and wait for new
assignment
ENTDAA
Enter Dynamic Address
Assignment
Broadcast Write 0x07
Enter Controller initiation of Dynamic Address Assignment
Procedure
SETDASA
Set Dynamic Address from
Static Address
Direct Write 0x87
Controller assigns a Dynamic Address to a Target with a
known Static Address
SETNEWDA
Set New Dynamic Address
Direct Write 0x88
Controller assigns new Dynamic Address to a Target
SETMWL
Set Maximum Write Length
Broadcast Write 0x09
Direct Write 0x89
Controller sets maximum write length
SETMRL
Set Maximum Read Length
Broadcast Write 0x0A
Direct Write 0x8A
Controller sets maximum read length and IBI payload size
GETMWL
Get Maximum Write Length
Direct Read 0x8B
Controller queries Target’s maximum possible write length
SETBUSCON Set Bus Context
Value
Broadcast Write 0x0C
Brief Description
Controller specifies a higher-level protocol and/or I3C
specification version
GETMRL
Get Maximum Read Length
Direct Read 0x8C
Controller queries Target’s maximum possible read length
and IBI payload size
GETPID
Get Provisional ID
Direct Read 0x8D
Controller queries Target’s Provisional ID
GETBCR
Get Bus Characteristics
Register
Direct Read 0x8E
Controller queries Target’s Bus Characteristics Register
GETDCR
Get Device Characteristics
Register
Direct Read 0x8F
Controller queries Target’s Device Characteristics Register
ENTHDR0
Enter HDR Mode 0
Broadcast Write 0x20
Controller has entered HDR-DDR Mode
ENTHDR1
Enter HDR Mode 1
Broadcast Write 0x21
Controller has entered HDR-TSP Mode
ENTHDR2
Enter HDR Mode 2
Broadcast Write 0x22
Controller has entered HDR-TSL Mode
ENTHDR3
Enter HDR Mode 3
Broadcast Write 0x23
Controller has entered HDR-BT Mode
RSTACT
Target Reset Action
Broadcast Write 0x2A
Direct Write & Read 0x9A
Controller configures and/or queries Target Reset action
and timing
GETSTATUS Get Device Status
Direct Read 0x90
Controller queries Target’s operating status
GETMXDS
Direct Read 0x94
Controller queries Target’s maximum read/write data
speeds and maximum read turnaround time
Get Maximum Data Speed
siliconchip.com.au
Australia's electronics magazine
October 2024 31
Fig.6: dynamic addresses can be assigned
by two methods – from a static 7-bit address
using the SETDASA CCC, or via the Dynamic
Address Assignment process started by the
ENTDAA CCC. The latter is preferred; in
this case, bus arbitration is used to assign
addresses to all devices in sequence.
Fig.7: the Provisioned Identifier (PID) is a 48-bit value containing a manufacturer ID, a part ID, an Instance ID and
a 12-bit device characteristic descriptor. On some parts, the Instance ID is programmable via pins or other means to
allow multiple instances of the same device to be uniquely identified on the bus.
There are two different options
for assigning dynamic addresses.
Some early devices do have a static
7-bit address, which is used to assign
a dynamic address using the CCC
“Set Dynamic Address from Static
Address” (SETDASA), as shown at the
top of Fig.6. The static address can’t
be used for any other purpose.
The controller starts the transaction
in the usual way, sending the SETDASA CCC, followed by a restart, then
the static address of the target with
the read/write bit set. When the target ACKs the static address, the controller sends the dynamic address it
wishes to assign.
The controller can optionally set
further dynamic addresses by repeating the process after issuing a repeated
start condition.
This approach does not really help
with the problem of address duplication, so the preferred option is to assign
dynamic addresses based on a 48-bit
device identifier known as a ‘Provisioned ID’ (PID), the format of which
is shown in Fig.7.
The upper 15 bits of this are the
manufacturer ID assigned by the MIPI
Alliance. The next bit, #32, is usually
zero, while the following 16 bits are
the part identifier. Bits 12 through 15
32
Silicon Chip
are an instance ID. These may be programmed by setting device pin(s) to
specific levels, to allow the user to
deploy multiple instances of the same
device on the same bus.
The process for assigning dynamic
addresses to these targets relies on the
same bus arbitration mechanism we
saw earlier. The lower part of Fig.6
shows this in action. The CCC Enter
Dynamic Addressing Assignment
(ENTDASA) is sent, followed by a
repeated start condition and another
0x7E address.
Any targets on the bus that do not
have a dynamic address assigned
will ACK this and begin writing their
48-bit PID, followed by the contents
of two 8-bit capability registers, BCA
and DCA. This write is arbitrable, so
only the device with the lowest PID
will complete the process, at which
time the controller sends the dynamic
address it wishes to assign.
If the device acknowledges, the
dynamic address is considered
assigned. A repeated start condition
is issued, and the whole process is
repeated for the remaining targets
with unassigned dynamic addresses
until none are left. At that point, the
0x7E address is passively NACKed,
and the assignment process is terminated.
Hot-Join mechanism
Fig.8: the hot join process is
similar to the IBI process, except
that the joining device uses the
special 0x02 address. If the
controller ACKs the request, the
target waits for a dynamic address
to be assigned by the controller.
A target may join an I3C bus once
it is up and running (for example, by
being plugged in or powered up). It
does this using a mechanism similar
to the In-Band Interrupt, shown in
Fig.8. The hot-joining device emits
an address header with the special
high-priority address 0x02, guaranteeing it will be heard.
The controller may accept the hotjoin request by ACKing it or reject it by
NACKing it. If the request is accepted,
the joining device waits for the controller to assign a dynamic address via
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Fig.9: the I3C controller produces the SCL clock with a duty cycle such that the high period is 40ns or less. I2C devices
are required to have a 50ns glitch filter on their SCL and SDA inputs, so the I3C clock should be invisible to them.
Fig.10: the HDR exit and restart
patterns; the exit pattern is always
followed by a stop condition and
returns the bus to the idle state.
The restart pattern is analogous to
the repeated start condition and
delineates multiple messages within
an HDR transaction.
the ENTDAA CCC process described
above. If the controller rejects the
request, the joining device will likely
continue to make requests unless
the controller switches off hot-join
requests via the DISEC CCC.
Note that this process works if more
than one device joins simultaneously
– the 0x02 address will be emitted by
all devices simultaneously, and they
will all succeed in the arbitration. The
controller ACK will put them all in a
state awaiting dynamic address assignment, and the ENTDAA assignment
process will assign them all addresses
in order of their PIDs.
I2C compatibility
I mentioned before that I2C targets
can co-exist with I3C targets on the
same bus. It is important that these
devices don’t react to I3C messages
and potentially disrupt them. I3C uses
a couple of mechanisms to reduce the
chance of that happening. Firstly, the
special address 0xFE in the header of
I3C messages is a reserved address in
I2C and should be ignored by all complying devices.
On top of this, I3C takes advantage
of the 50ns glitch filter that is required
by the standard on the SDA and SCL
pins of I2C devices. The duty cycle of
the SCL signal is managed so that the
clock high period is always less than
or equal to 40ns, making the I3C clock
‘invisible’ to I2C targets. They should
ignore any signal on their SDA line,
because they don’t see any clock transitions on SCL.
Fig.9 shows how this works. For the
12.5MHz push-pull clock, the high and
low pulses are naturally 40ns long at
a 50% duty cycle. The 2.5Mhz opendrain clock is emitted at a duty cycle
of around 10%, leaving the high pulses
40ns long.
This behaviour is only needed if
there are legacy devices on the bus.
Most controllers allow for a 50% duty
cycle to be used on both clocks for
‘pure’ I3C buses.
When communicating with I 2C
devices, the SCL clock is reduced to
400kHz or 1MHz with a 50% duty
cycle and transactions are carried
out in open-drain mode with signalling conforming to the I2C standard.
However, I3C does not support the
I2C features of 10-bit addressing, clock
stretching or multi-master operation,
so be careful.
High data rate modes
So far, everything we have covered is occurring in ‘Single Data Rate’
(SDR) mode. The I3C protocol supports several higher data rate (HDR)
modes. I am only going to cover the
most common one of those in the
interests of brevity. Regardless of the
HDR mode chosen, the I3C bus is
always initialised and configured in
SDR mode.
Only limited extra functionality
is available in the HDR modes – you
can’t assign dynamic addresses or
receive in-band interrupts, for example.
HDR modes are always entered from
SDR mode by issuing the appropriate
Enter HDR Mode X (ENTHDRx) CCC.
Once entered, the HDR mode has a buswide effect until it is exited via an HDR
exit pattern. Within an HDR mode
transaction, multiple messages can
be separated by HDR restart patterns,
Fig.11: HDR-DDR transactions begin with an ENTHDR0
CCC, followed by a command and address word. Data
is then sent one word at a time to or from the controller,
depending on the command. The last data word is
followed by a five-bit CRC and an exit or restart pattern.
siliconchip.com.au
Australia's electronics magazine
October 2024 33
analogous to the repeated start condition in SDR mode.
The HDR exit and restart patterns
are shown in Fig.10. The exit pattern
is defined as four consecutive falling
edges on SDA while SCL is low. It is
always followed by a stop condition.
The restart pattern is defined as two
successive toggles of SDA (fall, rise,
fall, rise) followed by a rising edge
on SCL.
Fig.12 shows how the command, data
and CRC words are constructed.
The Command and CRC words
begin with the same preamble but are
distinguishable by context – the command word only ever comes immediately after entry to the HDR mode or
a restart pattern, while the CRC only
ever comes after a data word. Only a
very limited range of CCCs are supported in HDR-DDR mode.
HDR-DDR
Other features
The common HDR Double Data
Rate (HDR-DDR) mode uses the same
12.5MHz clock as SDR mode but
allows data bits to be sent on both rising and falling clock edges, effectively
doubling the data throughput.
Fig.11 shows how a typical HDRDDR transaction works. After sending
the ENTHDR0 CCC in SDR mode, the
bus switches to HDR-DDR mode. The
controller then issues a command and
address word indicating the data direction (read or write) and the intended
target’s dynamic address, followed
by one or more data words written
by either the controller or the target,
depending on the data direction.
When all the data has been sent, the
sender concludes with a five-bit CRC.
The controller then emits a restart pattern if another DDR message is to be
sent, or an exit pattern and stop condition if not.
The basic unit of transmission
(except for the CRC) is a 16-bit word
with a two-bit preamble and two trailing parity bits, for a total of 20 bits.
DDR mode can achieve an effective
data throughput of 20Mbps, comparable with SPI (but with error checking). Faster HDR modes are possible,
including some that allow for two or
four data lanes and can achieve effective data rates of up to 96Mbps. However, not all modes are supported by
all targets.
In addition to those features
described here, I3C offers some other
interesting capabilities, including
the ability to reset targets (individually or in groups) over the bus and
to send synchronising ‘ticks’ to targets to coordinate timing. It supports
group addressing, where a set of targets share a group address (alongside
their individual dynamic addresses),
so they can be sent messages simultaneously.
It is also possible for one target to
communicate directly with another via
device-to-device tunnelling. There is a
lot to this standard; it will be interesting to see what features receive support from chip vendors.
Trying it out
I have experimented with I3C over
the last couple of weeks, using an
NXP LPC865 microcontroller with an
integrated I3C controller. For targets,
I tried a Bosch BMI323 inertial measurement unit (IMU), an ST Microelectronics LPS22HH humidity sensor and a TDK ICM42688P motion
sensor.
I was able to test a lot of the SDR
functionality, and it works as advertised, but the experience was not as
smooth as it could have been. I think
these rough edges are due to the relative immaturity of the standard. The
device data sheets were a mixed bag
regarding the thoroughness of their
documentation of I3C features – I did
have to resort to a bit of trial and error
to get things going.
The MCU toolchain and the I3C
driver provided in the SDK worked
fine for my purposes. Debugging the
bus was a challenge, as my logic analysers do not currently have support for
the I3C protocol. For this reason, I had
to resort to printing out waveforms and
marking ones and zeros by hand on a
few occasions.
I am sure that all of these points
will improve as I3C becomes more
common. Right now, I3C is available
on only a limited number of devices,
which are helpfully listed at https://
binho.io/blogs/i3c-reference/i3c-
devices
I believe this list will grow, given
that the MIPI Alliance lists almost
every silicon vendor as a member,
and it has a pretty good track record
of establishing standards. Over the
next few years, I suspect we will see
I3C becoming more and more popular.
References
Fig.12: data is transmitted on both clock edges in HDR-DDR mode. For data
and command words, a two-bit preamble is followed by 16 data bits and
two parity bits. The CRC word is slightly different and is always followed
by a restart or exit pattern.
34
Silicon Chip
Australia's electronics magazine
I 2C-Bus Specification and User
Manual (2021): NXP, siliconchip.au/
link/abtv
I3C and I3C Basic specifications:
MIPI, siliconchip.au/link/abgm
ICM-42688-P: TDK, siliconchip.au/
link/abtw
Bosch Sensortec BMI323 Inertial
Measurement Unit (IMU): Bosch,
siliconchip.au/link/abtx
Arm Cortex-M0+ LPC86x 60MHz
32-Bit Microcontrollers (MCUs): NXP,
siliconchip.au/link/abty
STMicroelectronics LPS22HH
High-Performance MEMS Nano Pressure Sensor: ST, siliconchip.au/link/
abtz
SC
siliconchip.com.au
OCTOBER
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B 0010
CIRCUIT NOTEBOOK
Interesting circuit ideas which we have checked but not built and tested. Contributions will be paid for at
standard rates. All submissions should include full name, address & phone number.
Three-phase sinewave generator with TL074s
The entry in Circuit Notebook for
a three-phase generator using the
LM3900 Norton current-feedback op
amp caught my eye (“Three-phase
sinewave generator”, April 2023 issue;
siliconchip.au/Article/15746).
I vaguely remember the chip hitting the market around 1973, but I did
not have any experience with it then.
So I thought this was a good time to
catch up.
I wanted to build it to demonstrate
three-phase systems to first-year engineering students.
siliconchip.com.au
Unfortunately, I had difficulty
maintaining oscillation in the oscillator stage. It seemed that the ratios
of both the resistors and capacitors
were critical for maintaining oscillation. Having fixed that, the oscillator produced a sinewave with distortion (to be expected) on the negative
excursions.
But I just could not get the
phase-shifting circuitry to work. I
built it in isolation on the breadboard,
separate from the oscillator, but had
no success with it.
Australia's electronics magazine
So I decided to build the buffered
phase-shift oscillator using just a few
op amps (the venerable TL071/2/4
types) and RC networks. Next, I
devised a section to provide two signals that would be phase-shifted, one
leading and the other lagging. Combined with the direct output from
the oscillator, they provide three sine
waves of roughly equal amplitude,
120° apart.
The nominal frequency for the
oscillator section is 13.96kHz (1.732
÷ [2πRC]) with the values used (measured at 13.4kHz). Each stage in the
oscillator (IC1a-IC1d) provides a
phase shift of 60°. The tangent of 60°
is 1.732, hence the formula.
Each section attenuates the signal
by half (-6dB), so overall, the attenuation factor is 8 (23). Thus, the amplifier needs a gain of eight times. The
39kW/4.7kW divider provides a gain
of 8.3 times, which is close enough.
The four buffers prevent the RC sections from loading each other. Alternatively, a chip like the XR2206 could
be used as the oscillator, with the lead
and lag sections based on IC2c & IC2d
added to its output.
Allan Grant, Tutor,
Curtin Uni, Perth, WA ($100).
October 2024 39
Micromite Plus Explore 100-based Reflow Oven Controller
Phil Prosser presented an excellent Reflow Oven project in the April
& May 2020 issues (siliconchip.au/
Series/343). I sourced a small forced
convection oven for about $100 and
was able to modify it to bring out the
fan drive. But getting the cover off
proved a real chore, and in retrospect,
I would not recommend this approach
to any but the most enthusiastic!
Anyhow, I was able to neatly fit an
IEC socket to the cool rear panel of the
oven – and move the fan wires over to
it – a very safe installation.
Unfortunately, this oven has quartz
tubes as elements, which significantly
increase the heating time constant
of the system. Still, the temperature
tracked similarly to what Phil reported
in his article, probably due to improved
convection provided by the fan. I successfully reflowed numerous boards
with it, including some with TSSOP
and QFN chips. None required any
rework.
My motivations for migrating Phil’s
design to an Explore 100 included:
• I had an Explore 100 on hand
and wished to learn GUI controls and
explore capabilities.
• The colour LCD touchscreen is a
superior way to interface with it.
• The touchscreen eliminates a
rotary encoder, multiple PCBs, ribbon
cables and IDC connectors.
• MMBasic is likely easier for hobbyists to understand, so they can modify the code if desired.
40
Silicon Chip
Fig.1: the temperature compensation scheme.
I replicated all of Phil’s controls, but
one advantage of my design is that it
includes a compensation system that
significantly reduces the temperature overshoot. This works using an
‘internal feedback’ model, where the
software simulates the reaction of the
oven to inputs (Fig.1). With correct
tuning – see the screen grab overleaf,
this allows the oven temperature to
track the desired profile (Fig.2) closely.
The wiring is simple, as shown in
Fig.3. If you have an Explore 100 on
hand, you can load my software to
experiment with it from your desktop.
You just need to add the thermocouple
amplifier to see real temperature readings and add a 4.7kW resistor in place
of the solid-state relay (SSR) so that the
screen will correctly show when it is
trying to switch the heating element on.
Firstly, update the Explore 100 firmware to MMBasic Ver 5.05.05 (HEX
file available from https://geoffg.net/
micromite.html) if it’s older than that.
Next, plug in a USB cable to connect
Australia's electronics magazine
the Explore-100 to your PC. Once it is
detected, connect to its virtual serial
port using a terminal emulator at a
baud rate of 38,400, 8 bits, no parity,
two stop bits, and no flow control. Set
the terminal size to 100 × 70 characters and mode to VT100 with CR for
send & receive and UTF-8 coding (I use
Tera Term, but other emulators should
have similar options).
Pressing Ctrl-C should now give you
a “>” prompt. You can then set some
Options, eg, “OPTION DISPLAY 60,
70”. My OPTION LIST is as follows:
OPTION AUTORUN ON
OPTION BAUDRATE 230400
OPTION COLOURCODE ON
OPTION DISPLAY 60, 70
OPTION LCDPANEL SSD1963_5,
LANDSCAPE, 48, 6
OPTION TOUCH 1, 40, 39
GUI CALIBRATE 1, 106, 3800,
2063, -1335
OPTION SDCARD 47
OPTION RTC 67, 66
siliconchip.com.au
You can enter each option as above
– skipping the RTC line if you don’t
have one fitted, and ignore the LCDPANEL, TOUCH, and GUI CALIBRATE
options if you have already set them.
You can enter GUI TEST LCDPANEL to
check the operation of the LCD – press
the space bar to exit the test. Note that
if you change the baud rate (as I have
done), you might need to also change
it in the terminal software.
If all goes well, you can press F11
(or type XMODEM RECEIVE followed
by Enter), then, on the top bar of Tera
Term, press File/Transfer/XMODEM/
send and select my software file (available for download from siliconchip.
com.au/Shop/6/510). After that, pressing F2 (or typing RUN followed by
Enter) should start the program.
On the first run, it will ask you if it
should reset to defaults – press “YES”
this first time and the startup page
should appear. The system will start
controlling the temperature, although
the measured temperature will show 0
if no thermocouple amp is fitted.
Pressing EDITS will take you to
another page showing several editing
option buttons while temperature control continues.
With the Controller operating, the
next step is to power it down and connect it to the oven. I used socket-tosocket jumper leads (Jaycar WC6026),
stripping one end bare as necessary.
Firstly, as per Phil’s recommendation, you need to set the thermocouple amplifier offset to 0. That involves
soldering a link between pins 2 (reference) and 3 (ground) on the AD8495
chip on the amplifier board. I fitted
straight pin headers to this board and
mounted it with an insulating pillar
– at the opposite end of the enclosure
from the power plugs etc.
The circuit diagram shows the wiring for both the thermocouple amplifier and SSR. All the wiring between
the mains input & output sockets and
the SSR must be mains-rated, properly
colour coded and fully insulated (eg,
with heatshrink tubing and/or neutral-
cure silicone sealant).
The next step is to calibrate the
gain and offset values for the thermocouple while the Controller is on the
startup page. To do that, I dipped the
thermocouple tip into a glass of boiling water, then adjusted the gain to
match the reading on an industrial
glass thermometer. The temperature
Fig.3: the wiring
diagram for the
Reflow Oven
Controller to the
Explore 100.
siliconchip.com.au
Australia's electronics magazine
October 2024 41
falls rapidly; ideally, the water would
be kept boiling on a Bunsen burner or
the like for a constant 100°C. If you use
a metal container, use a peg or similar
to prevent the probe from touching the
metal surface.
Use a stirred ice bath (0°C) to adjust
the offset reading, then re-check the
scale again. In my case, the offset was
very close to 0, and the gain was 6.08
– these relate to Phil’s figures, except
I sum 32 voltage readings, so the values are scaled.
The internal photo was taken before
the Presspahn cover was fitted. The
firmware download includes the
BASIC code and a PDF document
describing how to tune the oven compensation parameters.
Finally, note that if you press and
hold down a SpinBox up or down
arrow, it will ‘auto-repeat’ at a fast rate
– as described in the Micromite Plus
Manual – a very useful feature. However, if you slide your finger to the side
instead of lifting it (easy to do inadvertently), the icon will stay coloured
(although the repeat will cease). This
will inhibit the opposing icon. The fix
is to tap the icon again.
Ian Thompson,
Duncraig, WA. ($150)
Supercap Boost Starter for Vehicles
If your car battery struggles to start
the engine, this low-cost project might
save replacing it and is a good excuse
to play with supercapacitors. The total
cost is about $25.
Six 120F 2.7V supercapacitors are
connected in series to give a bank
of 20F <at> 16.2V. The circuit board
includes resistors to balance the
charges on the capacitors.
When the pushbutton switch (S1)
is pressed, a DC-DC boost converter is
powered by the car battery and charges
the capacitor bank to 15.75V (16V
maximum), even though the battery
voltage will be much less than that.
The DC-to-DC converter briefly draws
20A while charging a ‘flat’ capacitor
bank. So use the appropriate wire
gauge and a heavy-duty momentary
switch.
The LED voltmeter connected to the
capacitor bank displays the charging
progress. So, just before starting the
car, hold S1 and watch the caps charge.
When the caps are charged, start the
car. As the key is turned to the ‘start’
position, the connection to the starter
motor solenoid or relay now powers
the 12V 200A relay and the capacitor
bank dumps into and parallels the
car battery.
The internal resistance of the capacitor bank is much lower than a wellworn car battery and provides the starting current. There is no need to keep
the caps charged all the time – only
just before starting the engine.
If you start the engine without
charging the caps first, the car battery
will have to charge the capacitors and
power the starter motor. A suitable
diode (shown as optional on the circuit) in series with the output from the
relay will prevent this, but I did not
think it was necessary as I like pressing the big red button!
If you want to add it, you can use the
VS-100BGQ045 (100A, 45V schottky
diode) or two in parallel for close to
200A (although they will not share perfectly, so probably more like 150A…).
My unit was assembled from modules I got from AliExpress: an Elnabrand supercapacitor bank, a 10A
boost converter (Core Electronics
018-DCDC-BOOST-150W; minimum
input voltage of 10.4V for a 16V output), a 12V 200A car relay (TN686),
a generic fuseholder with a 30A fuse
and a two-wire LED digital voltmeter.
You might wonder why I did not
use a Mosfet instead of a relay. It’s
mainly because I don’t have to worry
about protecting it from voltage spikes
or gate drive voltage requirements.
Relays are commonly used for car
starter motors, so they should not give
any trouble here.
You can see a video of my device
operating in the video at https://youtu.
be/zaLPW-d8fJg
John Russull,
Kratie, Cambodia. ($100)
The DC-DC
converter can
be purchased from
Core Electronics, or on AliExpress.
42
Silicon Chip
Australia's electronics magazine
siliconchip.com.au
GPS caravan clock and power monitor
This GPS-based clock will provide
the correct time no matter where you
are, whether in Australia or overseas.
It will also provide local sunrise and
sunset times, plus your altitude above
sea level. As a further bonus, it will
monitor your caravan’s DC voltage
and current.
It is driven by a Raspberry Pi. Any
model Pi will do; the smallest and
cheapest Pi currently available is the
model 3A+. The code is written in
Python, making it easy to customise
and extend.
The display is a Waveshare RPi
LCD High-Speed SPI Touch Screen
(Waveshare 15811), and it uses a four-
channel ADS1015 analog-to-digital
converter (ADC; Adafruit 1083) for
power monitoring.
Many 3.3V TTL GPS modules that
would work with this design are available, but I used the u-blox Neo-6M
from Altronics (Cat Z6333). The
upgraded Neo-7M sold in the Silicon
Chip Online Shop (SC6737) should
also work.
Raspberry Pi scripts are provided
with the software (link below) to make
installing the driver files for the Waveshare LCD easy. The Python code is
also part of that package.
Due to the LCD being attached to the
Pi’s only GPIO connector, it is necessary to solder wires for the GPS and
ADC modules. There are eight wires in
total. Fortunately, the LCD uses only
a few GPIO pins, leaving sufficient
spare ports.
Note that the GPS and ADC modules
are connected to the underside of the
Pi’s GPIO header so that the LCD can
plug into the top.
Assuming you start with a blank
Pi, begin by loading a microSD card
(16GB or greater) with the Raspberry
Pi OS (32-bit version recommended)
using the Raspberry Pi Imager. Details
and the download can be found at
siliconchip.au/link/absc
At the time of writing, the Waveshare LCD does not work with the
latest Raspberry Pi OS (Bookworm).
If you have problems getting the
LCD to work, try the Legacy version
(Bullseye). It can be found on the
“Raspberry Pi OS (other)” page of
the Imager.
Next, connect a monitor, keyboard
and mouse to the Pi; a wireless combo
keyboard/mouse makes it easier if
you are using the Model 3A, which
only has one USB port. Plug in the
SD card and attach the LCD. Connect
the Pi power supply and power it on.
After it boots up, run the configuration utility (raspi-config) to check
the settings.
Turn off Screen Blanking on the
Display tab to stop the clock from
disappearing due to the screen going
to sleep.
On the Interfaces tab, turn on SSH
and VNC. This provides a headless
display, so you do not need to plug a
monitor into the HDMI port. Enable
SPI for the LCD screen and I2C for the
ADS1015. Also switch on the Serial
Port option for the GPS module.
Ensure the Serial Console is off; otherwise, we will not be able to receive
messages from the GPS module.
Click Save and accept the reboot
request, then check your WiFi connection and download the files from
siliconchip.au/Shop/6/348 to your Pi’s
Home folder, then unzip the package
(“unzip Cara.zip”).
Enter the command “chmod +x
setupLCD” in the terminal to make
the file executable, then “./setupLCD”
to run the file. The driver files for the
LCD will automatically be downloaded and installed and then the Pi
will reboot. Watch for the diagnostic
messages on the LCD during boot-up
to confirm the drivers were correctly
installed.
Now re-open the terminal and enter
“chmod +x installLIBS” to make the
file executable, then “./installLIBS”,
which will install the necessary
Python libraries.
To use a VNC session with a different resolution to the LCD, run the
supplied “./start script” from an SSH
session (eg, via Putty). Make the file
executable with “chmod +x start”,
then run it. Direct your VNC viewer to
the Pi’s IP address (eg, 192.168.1.44).
To start the clock automatically on
boot, from a terminal, run:
sudo nano etc/xdg/lxsession/
LXDE-pi/autostart
Then, using the editor, add the following command before the <at>xscreensaver command:
<at>/bin/python home/pi/Cara.py
The current monitor I used does not
have a part number, but it is standard
in most vans with an output of 0-4V
for a current of 0-50A. An ACS712 30A
module could be used; they provide
66mV per amp (0-2V for 0-30A). That
requires changes to the code, but it is
easy to modify it to cater for any Hall
effect current sensor.
Dennis Smith,
Strahan, Tas. ($110)
siliconchip.com.au
Australia's electronics magazine
October 2024 43
By John Clarke
8-Channel Learning
IR Remote Receiver
This eight-channel relay board can have its outputs switched on and off using almost
any remote control, including universal types. Each output can be set to toggle on or off,
switched on for a fixed period, or on while the button is held down. The outputs can be
controlled by an onboard reed relay or a transistor; the latter can switch external relays.
W
ith so many appliances operated using
infrared (IR) remote controls, you
are bound to have at least one
remote that is not used anymore. With
our 8-Channel Learning IR Remote
Receiver, it can be put back in service
to provide control over eight separate
relay outputs to control low-voltage
DC or AC devices.
Many different kinds of remote control can operate the Receiver; you can
even use it with multiple remotes.
It learns the remote control code to
switch each of its eight outputs. You
could use a different remote control
unit for each output if you wanted to.
Most people would use a single remote
control, though.
Remote controls transmit signals
using specific IR protocols. These are
usually transmitted using an infrared
LED that is modulated on and off at
between 36kHz and 40kHz. The modulated signal is switched on and off in
a pattern with a start code, followed
by address and command codes (visible in Scopes 1 to 4).
The address determines what appliance the code is to control, such as a TV,
satellite decoder, DVD player, amplifier etc. The command code indicates
what function is to operate. This can
be power on or off, channel selection,
volume up, volume down, mute etc.
Our Receiver can be used with
remotes that produce signals in the
NEC, Sony, RC5 and RC6 remote control protocols. More information about
these is in a panel overleaf titled “Infrared Coding”. Many remotes will use
one of those protocols.
The controller has eight separate
outputs, and each one can be switched
using a separate code. Each channel
can either be controlled by a reed
relay (normally open contacts) or an
open-collector transistor. Reed relays
can be used for all channels, open
Fig.1: driving an external LED from
an open-collector output. With a
12V supply, the 390W resistor will
limit the current to around 25mA.
Fig.2: an opto-coupler’s outputs are
triggered by an internal LED, so
driving them is basically the same as
driving LEDs.
Fig.3: no series resistor is required
if the coil is rated at 12V DC when
driving an external relay from an
open-collector output.
44
Silicon Chip
Australia's electronics magazine
siliconchip.com.au
Features
Learns infrared remote control codes
from a handheld IR remote
Supports four different IR protocols
1-8 output channels controlled by reed
relays or open-collector transistors
Can be used with external relays (12V DC
coil types)
Eight LED channel status indicators
Momentary or toggle operation on each
output
Adjustable timer for momentary outputs
(125ms to 32s)
Timer settings are shown on an 8-LED dot
bargraph
Specifications
IR reception range: typically 10m
Power supply: 12V DC at 150mA+ (external
relays may require more current)
Output switching: up to 24V <at> 500mA
IR codes supported: learns NEC, Sony and
Philips RC5/RC6 remote protocols
Momentary mode: 16 timer values, from
125ms to 32 seconds
Output toggle rate: minimum cycle time
of 600ms
Oscillator frequency adjustment: ±6% in
128 steps
Power-on indication: dimmed LED
collector outputs for all channels or a
mixture of the two.
Both output types can switch LEDs
or other low-current loads. Alternatively, the transistor outputs can drive
relays with 12V DC coils and contacts
that can handle higher voltages and/
or currents.
You don’t need to build the controller with all eight outputs if you don’t
need them; just make it with fewer if
that’s all you need.
Outputs
The reed relays are ideal for switching low voltages (up to 24V maximum)
and currents up to 500mA. They can
be used to trigger pushbutton switches
on equipment by wiring the reed relay
contacts across the switch.
A reverse-biased diode should be
connected across the relay’s contacts
if switching inductive loads. Never
use the onboard reed relays to switch
mains voltages directly. Neither the
relays nor the PCB tracks can handle
that. If you need to switch higher voltages, use the open-collector transistor
outputs to switch appropriately-rated
external relays.
Any external relays used for mains
switching must be built to comply with
mains voltage safety standards, including using correctly rated wire of the
right colour and adequate insulation.
Figs.1-4 show a few different ways
you can use the eight outputs when
they are driven by open-collector transistors. Fig.1 shows how you can drive
an external LED, Fig.2 shows how an
external opto-coupler can be switched,
Fig.3 shows how to drive an external
relay and Fig.4 shows how you can
switch off or control the direction of
a motor.
With the motor, you can use the
channels with the outputs set for
momentary or toggle operation. In the
momentary mode, pressing (and holding) the button for open-collector output X activates RELAY 1 and causes
the motor to rotate one way, while
pressing the button for output Y activates RELAY 2 and causes the motor
to rotate the other way.
With both outputs set for toggle
operation, the motor will be stopped
until one of the outputs is toggled.
Its direction of rotation will depend
on which output is switched on. The
motor can then be reversed by toggling
both outputs, or stopped by toggling
either output.
Scope 2: an oscilloscope capture of
the output of IRD1 when receiving a
Philips RC5-coded signal.
Scope 3: an oscilloscope capture of
the output of IRD1 when receiving a
Sony-coded signal.
Remote control protocols
Scope grabs 1-4 show captured
waveforms for decoded IR signals
transmitted in the RC6, RC5, Sony and
Fig.4: a simple
method to control
the direction of a
motor using two
external relays,
driven from two
of the Receiver’s
outputs.
siliconchip.com.au
Scope 1: an oscilloscope capture of
the output of IRD1 when receiving a
Philips RC6-coded signal.
Australia's electronics magazine
Scope 4: an oscilloscope capture of
the output of IRD1 when receiving an
NEC-coded signal.
October 2024 45
A panel on Infrared Coding
Most infrared controllers switch their LED on
and off at a modulation frequency of 36-40kHz
in bursts (pulses), with the length of and space
between each (pauses) indicating which
button was pressed. The series of bursts and
pauses is in a specific format (or protocol)
and there are several commonly used. This
includes the Manchester-encoded RC5 and
RC6 protocols originated by Philips.
There is also the Pulse Width Protocol
used by Sony and Pulse Distance Protocol,
originating from NEC. For more details,
see application note AN3053 by Freescale
Semiconductors (formerly Motorola):
siliconchip.com.au/link/aapv
NEC protocols, respectively. These
waveforms were taken from the output of IRD1. The 36-40kHz modulation was removed by the receiver; its
output is low during the modulated
burst and high when there is a pause
in modulation.
Scope 5 shows the repeat pulses for
the NEC protocol that follow the initial
main code if the remote control button
is held down.
For the remaining protocols (RC5,
RC6 and Sony), holding down the
remote control button simply repeats
the code that is initially sent. More
details are provided in the “Infrared
Coding” panel.
Momentary & toggle modes
Each output can be set for momentary or toggle operation. With the
momentary selection, an output and
its associated LED switch on when the
remote control button is pressed, then
off again after a set period from ⅛th of
a second (125ms) to 32 seconds. The
timer period can be elongated by holding down the remote control button, in
which case the timer starts when the
button is released.
In toggle mode, the output switches
on with one press of an IR remote button, and it remains on until the same
button is pressed again, whereupon it
switches off.
During the IR code learning procedure, a pushbutton switch on the
controller board selects momentary
or toggle operation for each output.
For channels set to momentary mode,
the on-time period is set at the same
time, using a trimpot, with the front
panel LEDs indicating the period
selected.
46
Silicon Chip
Philips RC5 (Manchester-encoded) (36kHz)
For this protocol, the 0s and 1s are transmitted using 889µs bursts and pauses at 36kHz. A ‘1’ is an 889µs
pause then an 889µs burst, while a ‘0’ is an 889µs burst followed by an 889µs pause. The entire data
frame has start bits comprising two 1s followed by a toggle bit that could be a 1 or 0. More about the
toggle bit later. The data comprises a 5-bit address followed by a 6-bit command. The most significant
address and command bits come first.
When a button is held down, the entire sequence is repeated at 114ms intervals. Each repeat frame is
identical to the first. However, if transmission stops, then the same button is pressed again, the toggle
bit changes. This informs the receiver as to how long the button has been held down.
That’s so it can, for example, know when to increase volume at a faster rate after the button has
been held down for some time.
Sony Pulse Width Protocol (40kHz)
This is also known also as SIRC, which is presumably an acronym for Sony Infra Red Code. For this
protocol, the 0s and 1s are transmitted with a differing overall length. The pause period is the same at
600µs, but a ‘1’ is sent as a 1200µs burst at 40kHz, followed by a 600µs pause, while a ‘0’ is sent as a
600µs burst at 40kHz followed by a 600µs pause.
The entire data frame starts with a 2.4ms burst followed by a 600µs pause. The 7-bit command is
then sent with the least significant bits first. The address bits follow, again with least significant bits
first. The address can be five bits, eight bits or 13 bits long to make up a total of 12, 15 or 20 bits of data.
Repeat frames are the entire above sequence sent at 45ms intervals.
NEC Pulse Distance Protocol (PDP) (38kHz)
For the NEC infrared remote control protocol, binary bits zero and one both start with a 560µs burst
modulated at 38kHz. A logic 1 is followed by a 1690µs pause while a logic 0 has a shorter 560µs pause.
The entire signal starts with a 9ms burst and a 4.5ms pause.
The data comprises the address bits and command bits. The address identifies the equipment type that
the code works with, while the command identifies the button on the remote control which was pressed.
The second panel shows the structure of a single transmission. It starts with a 9ms burst and a
4.5ms pause. This is then followed by eight address bits and another eight bits which are the “one’s
Australia's electronics magazine
siliconchip.com.au
complement” of those same eight address bits (ie, the 0s become 1s and the 1s become 0s). An alternative version of this protocol uses the second series of eight bits for extra address bits.
The address signal is followed by eight command bits, plus their 1’s complement, indicating which
function (eg volume, source etc) should be activated. Then finally comes a 560µs “tail” burst to end
the transmission. Note that the address and command data is sent with the least significant bit first.
The complementary command bytes are for detecting errors. If the complement data value received is
not the complement of the data received then one or the other has been incorrectly detected or decoded.
A lack of complementary data could also suggest that the transmitter is not using the PDP protocol.
After a button is pressed, if it continues to be held down, it will produce repeat frames. These consist
of a 9ms burst, a 2.25ms pause and a 560µs burst. These are repeated at 110ms intervals.
The repeat frame informs the receiver that it may repeat that particular function, depending on what
it is. For example, volume up and volume down actions are repeated while the repeat frame signal is
received but power off or mute would be processed once and not repeated with the repeat frame.
Codes learned are stored in non-
volatile flash memory. This ensures
that the IR codes and other settings
like momentary/toggle and the timer
period are not lost if the power is
cycled. All outputs are initially off
when power is applied to the Receiver.
The 8-Channel Learning IR Remote
Receiver fits neatly into a compact
instrument enclosure. An acknowledge (ACK) LED and the eight channel
status LEDs are mounted on the front,
while the power input and channel
output connections are at the rear. A
12V DC plugpack or similar supply
powers the Receiver.
Circuit details
Philips RC6 (Manchester-encoded) (36kHz)
0s and 1s are transmitted using 444μs bursts with 444μs pauses at 36kHz. The entire data frame has
start bits comprising a 2.666ms burst followed by a pause for 889μs, then a ‘1’ bit. After this, there is
a 3-bit mode value, typically 000. The toggle bit comes after that; it uses an 889μs burst and 889μs
pause instead of the 444μs used for the Mode, Address and Command bits.
The data is an 8-bit address followed by an 8-bit command, with the most significant bits first. The
same sequence is repeated at 106ms intervals when a button is held down. If transmission stops and
the same button is pressed again, the toggle bit changes state. This lets the receiver determine how
long the button was held down.
Referring to the circuit diagram,
Fig.5, an infrared receiver (IRD1),
sends signals to a PIC16F1459 microcontroller (IC1), which drives reed
relays, NPN transistors or a combination of both, depending on how you
configure the PCB.
IRD1 includes an infrared detector,
amplifier, bandpass filter (typically
centred around 38kHz) and an automatic gain control (AGC). IRD1’s output is normally high (5V) but goes low
(near 0V) when it receives a 38kHz IR
signal. This means that the infrared
receiver removes the 38kHz modulation, with the output staying low for
the duration of the frequency burst.
The supply for IRD1 is derived via
a 100W resistor from the 5V rail and it
is decoupled by a 100µF electrolytic
capacitor. This is to keep electrical
noise out of the supply for IRD1; it
requires a steady supply as it contains
a sensitive, high-gain amplifier.
The infrared signal is modulated
so that the detector will ignore other
infrared sources, such as halogen
lamps, bar radiators and the sun. Bar
Scope 5: the repeat code sent by an
NEC-style remote control when you
hold down a button.
siliconchip.com.au
Australia's electronics magazine
October 2024 47
Fig.5: the main part of the circuit comprises microcontroller IC1, infrared receiver IRD1, a few LEDs and pushbuttons and
a simple linear power supply. While there are eight output sections, only two are shown; the other six are identical. Each
section can either have a reed relay (as shown in the boxes in the middle) or a transistor and diode (as shown on the right).
radiators and halogen lamps produce a modulated signal at 100Hz
(for 50Hz mains), while the sun produces a constant level of infrared that
can vary slowly over time. These are
all removed by the bandpass filter
within IRD1.
Many general-purpose IR detectors
centre the filter at 38kHz, allowing a
frequency range from 36kHz to 40kHz
to be received without too much attenuation from the bandpass filter. There
may be a small amount of attenuation that reduces the reception range
slightly, but not to any significant
extent. RC5 and RC6 encodings use
36kHz modulation, NEC uses 38kHz
and Sony uses 40kHz.
These varying frequencies mean we
have to compromise with the infrared
detector for it to work with all these
protocols, with 38kHz being the best
bet as it’s in the middle of the range.
48
Silicon Chip
IRD1’s output goes to the RA0 digital input of microcontroller IC1 (pin
19), which decodes the demodulated
signal pulses and drives the outputs
according to the infrared code sent
by the handheld remote. Each output
channel includes an indicator LED,
driven via a 1kW resistor, and either a
100W resistor to drive a reed relay or
a 470W resistor going to the base of an
NPN transistor.
If a reed relay is used, a reverse-
biased diode (D11-D18) clamps the
back-EMF voltage from the relay’s coil
as it switches off. If an output transistor is used instead, a diode (D1-D8)
clamps the back-EMF produced by any
external relay coil it might be driving.
Whenever the transistor is turned on,
the external relay will be on.
The circuit shows one output driven
by the RC6 digital output (pin 8) and
one driven by the RA5 digital output
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(pin 2), but six other outputs are also
available, for a total of up to eight.
Any output configured as an
open-collector type provides a +12V
terminal suitable for driving an external 12V DC coil relay. This comes from
the power input socket (CON9) via
reverse-polarity protection diode D9.
The acknowledge (ACK) LED, LED9,
is driven from IC1’s RC2 digital output
and flashes whenever an infrared signal is received. LED9 doubles up as a
power indicator by glowing at about
6% brightness when an IR signal is
not being received. The ACK LED also
provides indications during the process of learning infrared codes; more
on that later.
Pushbutton switches S1, S2 and
S3, connected to IC1’s RB5, RB6 and
RA1 digital inputs, are used during the
learning process. Those three inputs
are held high (at +5V) unless pulled
siliconchip.com.au
A bird’s eye view of the Learning Remote Receiver. The CON1-CON4 outputs are driven by transistors in this case, and
CON5-CON8 by relays. The board allows either style to be used to drive any of the eight outputs.
to 0V when the corresponding button
is pressed. The RA1 input is pulled
high via a 10kW resistor to the 5V supply, while the RB5 and RB6 inputs are
held high by pullup currents provided
internally by IC1.
Trimpots VR1 and VR2 provide
adjustments for the timer and IC1’s
oscillator. These connect to the AN5
and AN4 analog inputs, and IC1
converts the voltage at the wiper of
each trimpot to a digital value. VR1
allows the timer for each channel to
be adjusted from ⅛th of a second to
32 seconds.
Frequency adjustment
VR2 allows IC1’s internal oscillator
to be trimmed. Typically, it is set to its
mid position so IC1’s internal oscillator runs at the factory calibration
rate (usually within 3% of nominal
at 25°C). This oscillator is used as the
siliconchip.com.au
time base for decoding the IR codes.
Having an accurate time base provides
reliable IR code detection.
While handheld IR remotes should
transmit according to timing specifications, the timing can vary between
remotes because many use a relatively
inaccurate ceramic resonator for timing. These are used since they are
cheaper than crystals and also smaller.
The accuracy for low-cost versions is
typically ±5%.
While IC1’s decoding of IR signals
does have some tolerance, having the
adjustment allows for extra variation.
VR2 can be adjusted to accommodate
variations in IC1’s oscillator as well
as the IR remote control’s. It allows
IC1’s frequency to be adjusted by ±6%
in 128 steps.
The 5V supply for IRD1 and IC1
comes from REG1, a 78L05 regulator. A
100µF electrolytic capacitor bypasses
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its input, while a 10µF capacitor filters its output. IC1’s supply is also
bypassed by a 100nF capacitor close
to its supply pins.
Construction
All parts are installed on a PCB
coded 15108241 that measures 130
× 101.5mm. This can be housed in a
140 × 110 × 35mm plastic case, with
optional panel labels affixed to the
front and rear panels.
Fig.6 shows the layout of the
parts on the PCB with all eight reed
relays fitted. In contrast, Fig.7 shows
the identical layout but with open-
collector transistor outputs suitable for
driving external 12V DC relays or other
12V loads. You can mix and match the
two output types, and you don’t have
to populate all eight outputs.
As shown in the photos of our prototype, we installed open-collector
October 2024 49
Fig.6: the PCB populated with eight reed relays. With these relays, the outputs
are not polarised. You don’t need to install all eight relays if you need fewer.
transistor outputs for the first four
channels and relays for the last four
channels.
Regardless of whether you populate all eight outputs, you should fit
LED1 to LED8 and their associated
1kW resistors. As well as showing
activated channels, they display the
selected timeout period during the
learning procedure.
Begin assembly by fitting the resistors. The parts list shows the resistor colour codes, but you should also
check their values using a DMM before
soldering them to the PCB. Be sure
to fit the correct values for resistors
R1-R8: 100W for reed relays or 470W
for open-collector transistor outputs.
Keep the lead off-cuts, as you may
need them later.
The diodes can go in next. D11-D18
are 1N4148 types, while D1-D9 are
1N4004s. Take care that the diodes are
all orientated correctly.
Next, install the 20-pin DIL socket
for IC1 (notched end to the lower edge
of the PCB). The capacitors can then
be soldered in place, ensuring that the
three electrolytics are orientated correctly. The 100nF capacitor can be fitted either way around.
Follow by installing the DC socket
(CON9) and switches S1, S2 and S3.
After that, fit transistors Q1-Q8 and/
or relays RLY1-RLY8 with the notched
ends downwards. Be sure to place
REG1 (78L05) in the correct position.
It has the same TO-92 body as the
transistors.
Jumper wires JP1-JP8 can now be
installed in any channels where a transistor is fitted. These only need to be
very short (less than 5mm) and can be
fashioned from resistor lead off-cuts
bent in a ‘U’ shape.
Trimpots VR1 & VR2 can be installed
now, along with screw terminals
CON1-CON8. Ensure that the terminals
sit flush against the PCB and that their
wire entry holes are toward the board’s
top edge before soldering their pins.
LEDs & infrared detector
Fig.7: this is like Fig.6 but all eight output sections have been populated with
transistors. They can drive external loads directly or be used to control external
relays. You can also mix and match relays and transistors. The wire links feed
12V to the left side of the terminals (marked +).
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LED10 can be installed with its body
a millimetre or two above the PCB.
Be sure to install it with the correct
polarity: the longer anode lead goes
to the left, as indicated on the overlay
diagrams. Mount the remainder of the
LEDs, as shown in Fig.8.
Their leads must be bent down by
90° 6mm from their bodies. That’s best
done using a 6mm-wide cardboard
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Fig.8: bend LED1-LED9 like this
so they will reach the holes in the
front panel. Make sure you bend
the leads in the right direction so
that the longer (anode) leads will
be on the left when mounted on
the PCB, as shown in Figs.6 & 7.
Fig.9: similarly, by bending the
IR receiver leads like this, it will
reach the associated hole in the
front panel.
Using Figs.8 & 9, and
this photo as a reference, the
LEDs and IR receiver need to bent so
they fit into the front panel.
template. Make sure that each LED’s
cathode (K) lead (the shorter of the
two) is towards you before bending
it as shown. That way, the LEDs go
in with the correct polarity, with the
anode to the left-most hole in the PCB.
Don’t solder the LEDs to the PCB at
this stage. We’ll do that later, with the
PCB in the case.
Having prepared the LEDs, you can
now bend the infrared detector’s leads
as shown in Fig.9. Solder it in place
with the centre of its lens 9.5mm above
the PCB.
need to drill 6mm diameter holes for
the nine LEDs and their bezels, as well
as for the infrared receiver, IRD1. The
holes in the rear panel are for cable
glands and the DC socket.
We used two glands, but the total
number can be increased if you can’t
fit all the output wiring through just
two glands. Their holes should be at
least 22mm apart in the region shown.
The 12mm holes for the glands are best
made using a small pilot drill to begin
with, carefully enlarged to size using
a tapered reamer.
Drilling the case
Final assembly
The next step is to drill the front and
rear panels of the enclosure. The drilling template, Fig.10, shows where the
holes are located and their sizes. You
Once all the holes have been drilled,
the PCB can be placed into the case.
The nine LEDs can then be adjusted
by cutting the leads shorter if they hit
the base of the case. Next, insert the
LEDs into the front panel holes (without the LED bezels initially) and fit the
PCB and front panel into the enclosure.
Check that each LED is correctly orientated and that it protrudes through
its front panel hole before soldering
its leads on the top of the PCB. Once
they have all been soldered, remove
the board and also solder them on the
underside of the PCB, then trim the
leads further.
Now check that the infrared detector’s lens aligns correctly with its frontpanel hole. If not, bend its leads until
it’s centred.
Testing
Apply power using a 12V DC
plugpack and check that the voltage
Fig.10: the front and rear
panel drilling details.
These diagrams can be
printed/copied at actual
size and used as templates.
We drilled two 12mm
holes for cable glands, but
you can have up to four if
needed. Ensure they’re in
the specified zone and a
minimum of 22mm apart.
All dimensions are in
millimetres.
October 2024 51
between pins 1 and 20 of IC1’s socket
is close to 5V (4.85-5.15V). If no voltage is present, check diode D9’s polarity and the polarity of the 12V DC
supply (the centre of the plug should
be positive).
Also ensure that REG1 is correctly
orientated and all leads have been
correctly soldered to their PCB pads.
If the supply checks out, switch off
the power and install IC1, ensuring
that its notched end faces toward the
front and all its pins correctly go into
the socket.
Set VR2 to its mid position. VR1 can
be set fully anti-clockwise initially, for
a 125ms timeout, so it is easier to check
the momentary and toggle operations
for the channel outputs.
Learning codes
The 8-Channel Learning IR Remote
Receiver can learn infrared codes
matching NEC, Sony, RC5 and RC6
protocols. These are commonly used
in many handheld IR remote controls.
Each channel should be programmed using a different button on
the handheld remote. You don’t have
to use the same remote to operate each
channel. You can use different remote
controls, provided they produce one
of the supported protocols.
Once you start the learning mode,
you have 20 seconds to finish this procedure before it times out and returns
to the normal operating mode.
To program each channel, press the
Program switch (S1). This will fully
Parts List – 8-Channel IR Remote Receiver
1 double-sided PCB coded 15108241, 130 × 101.5mm
1 140 × 110 × 35mm plastic case [Jaycar HB5970, Altronics H0472]
2 panel labels, 131 × 28mm (optional)
1 12V DC plugpack rated at 150mA or more (see text)
3 SPST vertical tactile switches with ~0.7mm actuators (S1-S3)
[Jaycar SP0600, Altronics S1122]
8 2-way screw terminals, 5.08mm pitch (CON1-CON8; as required)
1 2.1mm or 2.5mm inner diameter PCB-mount DC socket to suit plugpack
(CON9)
2 10kW mini top-adjust trimpots (VR1, VR2)
[Jaycar RT4360, Altronics R2480B]
2 cable glands for 3-6.5mm cable [Jaycar HP0720, Altronics H4380]
1 20-pin DIL IC socket
9 5mm LED bezels
4 No.4 self-tapping screws
Semiconductors
1 PIC16F1459-I/P microcontroller programmed with 1510824A.HEX (IC1)
1 TSOP4838 or similar 36-38kHz IR receiver (IRD1)
[Jaycar ZD1952/ZD1953, Altronics Z1611A]
1 78L05 5V 100mA regulator (REG1)
8 high-brightness 5mm red LEDs (LED1-LED8)
2 high-brightness 5mm green LEDs or other colour (LED9, LED10)
1 1N4004 1A diode (D9)
Capacitors
2 100μF 16V PC electrolytic
1 10μF 16V PC electrolytic
1 100nF 50V MKT polyester or MLCC
Resistors (all ¼W, 1% axial)
1 10kW
11 1kW
1 100W
Extra parts for reed relay outputs (per output, up to 8 total)
1 SPST DIP 5V reed relay (RLY1-RLY8) [Jaycar SY4030, Altronics S4100]
1 1N4148 75V 200mA diode (D11-D18)
1 100W ¼W 1% axial resistor (R1-R8)
Extra parts for open-collector transistor outputs (per output, up to 8 total)
1 BC337 65V 100mA NPN transistor (Q1-Q8)
1 1N4004 1A diode (D1-D8)
1 470W ¼W 1% axial resistor (R1-R8)
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Silicon Chip
Australia's electronics magazine
light the ACK LED on the front panel.
One of the channel LEDs will also be
lit, showing the currently selected
channel.
Initially, this will be channel 1,
but other channels can be selected
by pressing the Channel switch (S2).
Each press will choose the next channel; after 8, it will return to channel 1.
The Momentary/Toggle (MOM/
TOG) LED will indicate the current
selection for that channel. It lights
for 125ms every second to show the
momentary selection, or lights solid
to show the toggle option is selected.
Pressing S3 selects between momentary and toggle action.
When momentary is selected, the
time the channel is on (once programmed) is set by the timer. The
timer value for the selected channel
is adjusted using VR1. Timer values
range from 125ms to 1s in eight 125ms
steps, then options of two, three, four,
five, six, eight, 16 and 32 seconds.
To set the timer, press and hold the
MOM/TOG switch for at least 600ms.
This will change the channel LEDs
from showing the selected channel to
displaying the chosen timer period
instead.
If VR1 is fully anti-clockwise, none
of the channel LEDs will light, but the
ACK LED will be fully lit. For other
timer periods, the ACK LED will be
off, and the 8-channel LEDs will show
the timer setting as per Fig.11, like a
dot bargraph.
Adjust VR1 for the timer period
required. When S3 is released, the
channel display and ACK LED will
siliconchip.com.au
return to showing the selected channel
and fully lit ACK LED to indicate that
it is still in the programming mode.
The MOM/TOG LED will flash
to show that momentary action is
selected. If you decide to change to
toggle, press S3 again and the LED
will stay lit, indicating toggle mode.
In this case, the timer for that channel
is inactive.
Once the channel has been selected
and the timer adjusted (or toggle
enabled), press S1. This makes it ready
to receive an infrared signal from the
handheld remote. The ACK LED will
flash in readiness, with the LED lighting for 125ms every two seconds.
A lack of flashes indicates that the
Receiver hasn’t accepted the code as
valid. It will flash at 1Hz with a
50% duty cycle. Point the handheld remote toward the receiver
and press a button on the handheld
remote. If the IR code is valid, the ACK
LED will flash once for an NEC code,
twice for a Sony code, three times for
an RC5 code and four times for an
RC6 code.
If you are sure that the code from the
remote should be valid, try adjusting
the VR2 frequency adjustment trimpot
to check if the code becomes valid.
You will need to select the learning
mode (S1) each time to test this. Use
small changes over the full range of
VR2 before rejecting the remote as
unsuitable.
If the code is accepted as valid,
the channel LED will light when the
programmed button on the handheld
remote is pressed again. For toggle
mode, the channel will be on with one
press of the handheld button and be
off on the next press. For momentary
operation, the channel will be on for
the timer’s duration.
In momentary mode, if the handheld
Up to four cable glands
can be fitted for the wiring to
CON1-CON8 although we found two
sufficient.
remote button is continuously pressed,
the channel will remain on until after
the button is released, plus the timer
period.
If you find that the unit doesn’t operate reliably or only works with certain
orientations of the remote, it may be
due to reception frequency tolerances.
In that case, it’s just a matter of altering
IC1’s frequency with VR2 to improve
the IR code detection.
Panel labels
Assuming it’s all working correctly,
all that remains now is printing out
and fitting the front and rear panel
labels. They are shown in Fig.12 but
are also available as a PDF download
from siliconchip.au/Shop/11/468
Information on making front panel
details is available on the Silicon Chip
website at siliconchip.com.au/Help/
FrontPanels
Once you have made the labels,
affix them in position and cut out the
holes using a sharp hobby knife. For
the front panel, insert the LED bezels
from the front and insert the LEDs from
the rear. The PCB is held in place with
No.4 self-tapping screws into the four
integral mounting posts at the bottom
SC
of the case.
Fig.11 (left): as you adjust
VR1 to set the timing for a
momentary output, the LEDs
will show the current setting
like this. Rotate VR1 while
holding S3 until the LEDs
show your desired output ontime, then release S3.
Fig.12 (right): the front and
rear panel labels. These
can also be downloaded as
a PDF from siliconchip.au/
Shop/11/468
siliconchip.com.au
Australia's electronics magazine
October 2024 53
The MG4 XPower
Electric Car
by Julian Edgar
No technological change seems to inspire love/hate emotions like electric vehicles (EVs). Many people are
either intensely for them or intensely against. The truth is much more nuanced, as Julian Edgar describes
after nine months and 20,000km with his MG4 XPower EV.
H
aving been interested in car tech
for over 40 years, I’ve watched
the advent of EVs with fascination.
I first drove a Tesla 15 years ago and
was enormously impressed. However, especially living in a rural area,
I couldn’t see the worth of buying an
EV until about nine months ago.
Then, an EV was released that, for
the first time in the modern history
of electric vehicles, had a significant
advantage over any new internal combustion engine (ICE) car in existence.
That advantage was the price for the
level of performance!
With the release of the Chinese-made
MG4 XPower, extraordinary performance became available at a cost that,
in round terms, was about half that of
an equivalent ICE car. For $60,000,
you can now get performance that is
the province of ICE cars costing at least
$120,000. That is simply incredible; it
is the most significant change in cars
I have ever seen.
Of course, if the car itself were
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terrible, that apparent advantage
would count for nought. I went to a
dealer and drove the MG4 XPower
and was very impressed, so I bought
it. Now, nine months later, what do I
think of the MG4 – and of owning an
EV, generally?
The MG4 XPower
The venerable UK brand MG has
been owned by Chinese company
SAIC Motor since 2007 (although it
was initially acquired from BMW by
another Chinese company in 2005).
While the company maintains a small
UK design base, perhaps 95% of the
car is designed and manufactured in
China.
A mid-sized hatchback (some people say the car is small; it could only
be termed that in an era when very
large cars have been normalised), most
models of the MG4 use a rear-mounted
150kW electric motor and a 64kWh
400V lithium-ion battery pack. That
under-floor battery weighs 409kg.
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The sportier XPower uses a 170kW
rear electric motor and a 150kW front
electric motor, both of which are threephase, permanent magnet synchronous designs. Compared to the standard car, the XPower has larger brakes,
revised suspension and different interior and exterior trim. Its claimed
0-100km/h time is just 3.8 seconds.
That is phenomenally fast – as fast
as a Ferrari from a few years ago. The
XPower weighs 1800kg, which is not
particularly heavy in today’s terms.
As opposed to a hybrid car that
uses a combination of an ICE engine,
HV battery and electric motor, an EV
must be charged from mains power.
The time that takes depends on the
car itself and the charger to which it
is connected. With the MG4, the DC
charging power to the battery pack
can be up to 140kW, meaning that
a normal 10% to 80% charge takes
about 30 minutes (charging speed
isn’t linear).
Of course, that’s only when using
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The Chinese-built MG4 is one of the new breed of cost-effective electric cars currently available. This is the XPower
version, a very fast car priced about half the equivalent car with a petrol engine. The high-voltage battery is mounted
under the floor, with clever styling disguising the increased height of the lower edge of the doors.
a high-power charger such as those
found at highway rest stops, shopping
centres and the like. Using the provided AC charger (termed by many a
‘granny’ charger because it is so slow!),
it takes more than 20 hours to charge
the battery fully.
I use an aftermarket 3.6kW charger
powered from a dedicated 15A home
socket, which will charge the battery
to 80% overnight from a starting level
of about 20%.
Electric power is limited when the
battery charge drops below about 25%;
as the battery charge decreases below
that, the available power continues
to decline.
This caused us a problem only
once, when my wife was driving home
with a very low battery level and
had to climb a long highway hill. In
that case, the car would only achieve
80km/h, which was a bit dangerous
on a 110km/h road.
The official energy consumption
of the XPower is 19kWh per 100km.
That has proven accurate in summer
conditions, but the consumption is a
bit higher in winter – nearer 20kWh
per 100km. With a 64kWh battery, and
working from 80% to 10% capacity,
the range is about 230km.
Why only 80% to 10%? The manufacturer suggests using the battery
in that way under normal conditions
and only tapping into the full capacity
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when undertaking long trips. Using
the full battery capacity gives a range
of about 330km, but doing that frequently will degrade the battery prematurely.
The displayed battery range is very
accurate. Initially, I was fearful of letting the battery level get below about
15%. Judging the remaining range of
ICE vehicles based on fuel levels can be
hit and miss, so I thought the MG4 display might suddenly drop from 15%
to zero, stranding me by the side of
the road and requiring a flatbed truck
to get me home!
However, I now realise there are no
problems in running the battery down
to, say, 5% as the change in the predicted range corresponds very well
with the distance travelled.
As with all EVs, the MG4 uses regenerative braking (ie, it returns power
to the battery under braking). This is
achieved in two ways. The first way is
as you lift the accelerator pedal, the car
automatically starts to brake regeneratively, a bit like engine braking with an
ICE car in gear. The amount of regeneration can be seen on the driver display; it is seamlessly varied with the
right foot.
The second way regenerative
As with many modern cars, instruments and most controls are via LCD screens.
The centre is a touch screen; the buttons below it are the only buttons on the car!
Australia's electronics magazine
October 2024 55
The environmental footprint
One reason many people are for or against EVs relates to the environmental
footprint. There is so much information (and misinformation) on this
topic. However, major peer-reviewed studies show that the total lifecycle
environmental footprint (including building the car, running it and disposing
of it) is less for an EV than an ICE car.
That is the case even when the EV is charged mainly from coal power.
However, hybrid cars can be very close depending on the exact power-generating
mix. But for me, some of this debate loses the wood for the trees: it’s far better
for the environment to ride a bicycle or take public transport. Or even to retain
the old ICE car and use it only for short trips.
braking occurs is when the brake pedal
is pressed. That increases the level
of regeneration over that achieved
by lifting your foot off the accelerator pedal and, if the brake pedal is
applied harder, the friction (conventional) brakes also help to slow the car.
Regenerative braking is so effective
that the disc brakes become slightly
rusty from a lack of use and can squeak
a little when applied. One hard braking
event then cleans them again.
The stand-out feature of the XPower
is its amazing drivetrain. With 600Nm
of torque, the XPower is extraordinarily strong, linear, refined and
responsive. The only ICE car I’ve
driven that comes close to its effortless performance is a twin-turbo V-12
Mercedes and, of course, the XPower
is much faster.
We’re talking about a wave of torque
that just hurls the car forward, making driving situations like overtaking
on country roads ridiculously easy.
The drivetrain is the most impressive
I have driven in 35 years of professionally testing cars; it makes my Porsche
981 Cayman engine and transmission
look positively agricultural.
The ability to ‘play a tune’ on the
accelerator pedal, seamlessly moving
from immense power to braking, is
simply wonderful. It’s a delight I enjoy
every time I get into the car, whether in
city stop/start traffic or driving down
a twisty country road.
The design and build quality of the
MG4 are excellent. The paint is very
good and panel margins (gaps between
adjoining panels) are consistent. Even
when delving under the plastic covers positioned over so many of the
mechanicals, the engineering and
build quality look good.
You must search hard to find deficiencies, but an example is the stitching on the underside of the head
restraints. It looks as if the person
operating the machine was looking
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Silicon Chip
the other way at times!
The interior of the car is quite minimalistic; some would call it plain.
There are the two displays, a short
row of buttons, a charging pad for your
phone and not much else. To some
people, it looks cheap and nasty; to
others, it is sleek and modern. I fall
midway between the two camps – I’d
like to see more control buttons and
bigger screens, but otherwise, the interior austerity doesn’t concern me.
Regarding the screens, the central
unit measures 10.25 inches (26cm),
but unfortunately, the screen behind
the steering wheel is only 7 inches
(18cm). With the small font that’s often
used, the latter can be hard to read
at a glance, although familiarity has
improved this.
Nearly all the controls are operated
through the central touch screen, with
only seven physical buttons provided
below it. The central screen can be
slow to react, especially when the car
is first started, and accessing controls
that in other cars would be a simple button-push away can become a
clumsy dance of fingers.
However, two of the steering buttons
are programmable so, for example,
some of the heater/air conditioner controls can be accessed through a steering
wheel button and then adjusted via a
steering wheel toggle.
The air conditioner uses a high-
voltage electric motor to power the
compressor and it works extremely
well. Heating is by a resistance heater
rather than using the air conditioning
system as a heat pump. Interestingly,
in some overseas markets, the MG4’s
heater does use the air conditioner;
they must not think it ever gets cold
in Australia!
The seats and steering wheel are
heated; these work very effectively,
and I tend to use these functions rather
than the cabin heater itself.
Where the technology fails – and it
Australia's electronics magazine
utterly fails – is in some of the driver
assistance systems. The Lane Keeping
Assistant is the worst. It is so bad that it
needs to be switched off; otherwise, it
beeps and yanks on the steering wheel
at every imagined driving misdemeanour. On unmarked country roads, it
is positively dangerous.
Frustratingly, it cannot be permanently disabled but must be switched
off every time the car is driven.
Another technology that is below
par is the active (radar) cruise control. It’s almost as if the system was
not recalibrated for the greater performance of the XPower, as it tends to be
too heavy-handed with both acceleration and braking. Certainly, any competent driver can be much smoother
than cruise control – in this regard,
even a 15-year-old Holden Commodore is much superior.
Other MG4 users have additionally reported autonomous braking for
phantom events; however, luckily, I
have not experienced that.
Hopefully, MG will release software
patches to solve these problems. These
require a dealer visit as no over-the-air
updates are available despite the car
having a 4G connection.
Editor’s note: given that some vehicles have been remotely ‘bricked’ or
had features removed after purchase,
I think that is a good thing.
The good and the bad of EVs
At this stage, and especially in rural
and regional Australia, EVs do not
make for a persuasive case for many
users. More than anything else, the
issues are range and charging infrastructure. Basically, for long trips, EVs
are terrible.
Sure, the web is full of EV discussion groups where people claim that
long trips are not only possible in
EVs but are, in fact, delightful. Just
stop every 2-3 hours for 30 minutes
of charging, and since those stops correspond to when you’d want a break
anyway, what’s the problem?
The reality is different. First, you
must find a high-speed charger –
and compared to ICE fuel pumps,
they are as rare as hens’ teeth, especially off main routes. Then, the charger needs to be available. Many are
broken, while others already have
EVs plugged in. Imagine how long a
fuel fill would take if every ICE car
required half an hour at the petrol
pump!
siliconchip.com.au
The XPower uses both front and rear electric motors, giving all-wheel drive.
This is the view under the bonnet. Its build quality is excellent overall.
The MG4 has a phone app that can
remotely check the battery level, lock
or unlock the car and turn on the
heater or air conditioner. Here, it is at
63% charge, charging at 2.7kW on its
way to 80%.
The XPower sits a bit higher than a traditional hatchback due to the underfloor battery pack. It helps to keep the centre of
gravity low.
siliconchip.com.au
Australia's electronics magazine
October 2024 57
Yes, you can do it, but taking an ICE
car with a decent range (these days, all
ICE cars) is vastly less stressful. On
a long trip, the ICE car is also much
quicker. Having tried it a few times,
I now rarely take my MG4 on trips
over 300km.
Next on the downsides is the financial uncertainty. People often quote
the meagre ‘fuel’ cost of an EV versus
an ICE car. And, especially if charged
from a home PV solar system, the running costs will indeed be a lot lower.
However, the major cost of buying a
new car is depreciation – the amount
the car loses in value each year.
At this stage, it very much looks like
EVs will have fast depreciation – that
has been the case in markets that are
more mature than Australia in terms
of EV penetration. There are several
reasons why.
First, as technology rapidly
improves, people value the older EVs
less highly. Second, battery life. While
the manufacturer often guarantees EV
batteries for a set period (eg, seven
years), the fine print shows that the
guarantee is typically for 70% charge
retention. Multiply the worst range by
0.7, and the real-world range of many
EVs is likely to become marginal without any real recourse.
And what if the battery degradation
is even greater than 70%? The reality
of older used EVs in Australia, like the
Nissan Leaf and Mitsubishi MiEV, is
that these cars often have a range that’s
now as little as 70-80km. Yes, they use
older battery technology – but they are
real examples of older EVs. Most ICE
cars still run just fine after 7-10 years
(as long as they’re maintained) and
don’t lose range.
Also, EV proponents often overlook the purchase cost. As the MG4
XPower demonstrates, in the expensive car market, EVs are now more
than competitive with ICE cars. But
what of those who are less wealthy?
A competent second-hand ICE car can
be bought for well under $10,000. No
such alternatives currently exist for
EVs.
As for the good aspects of EVs,
they require almost no maintenance.
I was initially sceptical of this, but my
MG4 XPower has not seen the inside
of a workshop in its first 20,000km.
The first scheduled service interval
is 40,000km – for most people, that’s
every three years! In terms of convenience, that is a major plus.
Driven hard, I don’t think the tyres
on my car will last more than about
30,000km, so it will be a tyre shop
that I first visit.
Another positive is that, depending
on your use, an EV is very convenient.
Plug it in each night just like your
phone, and it’s ready the next morning. No visits to petrol stations; just
unplug and go. And, as discussed, the
cost of charging an EV can be very low,
especially if charging during the day
from solar panels or using a low offpeak overnight tariff (where available).
I’ve already discussed driveability.
Truly, no ICE car can compete with the
superb flexibility and throttle control
that EVs have. Some people suggest
that EVs are rather uninvolving and
aren’t fun to drive – I think that is just
balderdash.
So where does that leave us? I love
the MG4 XPower. It’s a car that is practical, a joy to drive and gives me performance unmatched by anything at
its price. As for EVs in general, I think
that at this stage, they’re perfect for
some and quite unsuitable for others.
If you’re relatively wealthy, live in a
city, have PV panels (and especially
a storage battery) and commute daily,
they are perfect.
However, if you’re not very wealthy,
take many long trips and don’t have
a home charging facility with at least
3.6kW, steer clear for now.
If you’re listening to people discussing EVs and they say, “EVs are
fantastic!” or conversely, “EVs are
terrible!”, remember that they’re both
likely to be wrong. The truth is much
SC
more nuanced.
The XPower uses larger brakes and orange covers over the brake calipers. The brakes are strong but with regenerative
braking, they are seldom needed!
58
Silicon Chip
Australia's electronics magazine
siliconchip.com.au
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Using Electronic Modules with Jim Rowe
1-24V Adjustable USB
Power Supply
The “Zk-DP” is a surprisingly
inexpensive supply module that
converts 5V DC from a USB port
into any DC voltage between 1V and 24V at up
to 3W. It features a three-digit LED display showing the output voltage, plus
easy adjustment of the output voltage with a built-in multi-turn potentiometer.
A
lot of small electronic devices
now run from low-voltage DC.
Luckily, many can run from a 5V DC
supply, so they can be powered from
a USB port on your computer, a standard 5V USB mains power supply or
a portable battery bank.
But things are not so easy if a device
needs a supply of 9V, 12V, 15V, or
24V DC (or another ‘oddball’ value).
Usually, you must provide a separate
power supply or plugpack to deliver
the required voltage.
In those cases, it would be handy to
have a small, low-cost power conversion device that could take the power
from a standard 5V USB power source
and convert it into one of those other
voltages.
That’s precisely the function of the
module we’re looking at this month.
It plugs directly into a USB-A socket
providing 5V DC and can then power
a device at any voltage between 1V
and 24V DC. Despite its small size, it
can supply in excess of 3W of power
at any of those output voltages, eg,
250mA <at> 12V.
Setting the desired output voltage
is very easy, using a built-in multiturn potentiometer with an attached
knob and a tiny three-digit LED display that indicates the current output voltage.
From the legend on the PCB, it is
called the Zk-DP Desk Power module,
although it would also be correct to
call it a DC/DC voltage converter. It’s
currently available from several online
marketplaces at prices ranging from
$4.12 to $15.50 plus delivery.
We obtained the unit shown in the
photos via AliExpress from a supplier
called AGUHAJSU Global Purchase
Store for $4.12 plus shipping (a total
of just over $6). We noticed that the
Fig.1: a block diagram for the Zk-DP power supply module. Note that we
have not included values for the resistors and capacitors.
siliconchip.com.au
Australia's electronics magazine
same unit is also available from eBay.
The Zk-DP module is 70mm long,
26mm wide and 14mm tall (not including the spindle of the voltage adjustment pot). All the components are
mounted on a small PCB that’s 52.5mm
long and 21.5mm wide. The USB-A
input plug is at one end of the PCB,
while the voltage adjustment pot and
small 2-way output screw terminal
block are at the other.
All the electronics are housed in a
snap-together clear blue plastic case,
which allows the 3-digit output voltage indication to be easily read through
the case.
How it works
Some searching on the internet
didn’t reveal any circuit details of the
Zk-DP. Still, I was able to remove the
PCB from the case and glean enough
information to produce the block diagram (Fig.1). I was not able to determine the type of microcontroller
used as the ID marking on the top of
its 20-pin SSOP package had been
removed.
The five-pin SIL onboard programming header suggested it might be a
Microchip product. However, when
we compared numerous AVR and
PIC microcontrollers in that package
to the pinout used on the board, none
matched, so it’s probably something
else. Luckily, the SX1308 voltage converter chip still had its ID on top of its
6-pin SOT-23 package.
This device, shown just above the
centre of Fig.1, is designed as a boost
converter. However, it is being used
in a slightly different configuration
October 2024 63
These photos show the rear end and general view of the module with the
supplied blue plastic case. Note that there is not a cut-out for the 3-digit segment
display. Both photos are shown enlarged for clarity.
here, known as a SEPIC converter
(single-ended primary-inductor converter). This has a similar function to
a buck-boost converter but requires
just one switching element instead
of two. The operation is described at
https://w.wiki/9DjN
An ordinary boost converter (eg,
as shown in the SX1308 data sheet)
would have a series diode from pin 1
of U2 directly to the output. However,
that would mean the output voltage
could never go below 5V because there
would be a direct path for current to
flow from USB +5V through L2 and
that diode to the output.
Basically, the series capacitor AC
couples the switching waveform to
diode D1 so that there is no longer
a constant path for current to flow,
allowing the output voltage to be
regulated below the input as well as
above it.
The other inductor, L1, keeps the
load current flowing when the internal switch in U2 is closed and no current flows through the series capacitor
to the output. That means the output
filter capacitor does not have to supply the entire load current during this
time, significantly reducing the output
voltage ripple.
The SEPIC configuration is related
to the Ćuk converter (https://w.
wiki/9Db2), except that the positions
of the diode and second inductor (L1
here) are swapped. Thus, SEPIC gives
a non-inverted output voltage compared to the input. In contrast, the Ćuk
converter produces a negative output
voltage from a positive input.
The SX1308 runs at a fixed switching frequency of 1.2MHz and uses an
internal power Mosfet (with its drain
connected to pin 1) as a low-loss
switch. The output voltage is adjusted
by varying the voltage divider ratio to
send a proportion of the output voltage back to pin 3 of the SX1308, its FB
(feedback) input.
U2 varies the Mosfet duty cycle in
response to changes in the feedback
voltage. With a 50% duty cycle, the
output voltage is similar to the input
voltage of 5V. Higher duty cycles allow
the output voltage to go above 5V,
while lower duty cycles result in an
output below 5V.
The conversion efficiency is quite
high because the power Mosfet inside
the SX1308 has an on-resistance of
only 80mW (80 milliohms). For example, when configured as a boost converter and converting between a 5V
input and a 12V output, its efficiency
for load currents between 100mA and
400mA is better than 92%.
The microcontroller’s main job in
the Zk-DP module is to measure the
output voltage and show it on the small
3-digit LED display. The LED digits
are 6mm high and are quite readable.
Trying it out
After connecting the Zk-DP module to a bench power supply capable
of providing well over 3W, I also fired
up my bench DMMs and connected
them to the module’s output. I used
one to measure the module’s output
voltage, while the other measured the
current it delivered to a programmable
DC load. I used a third DMM to monitor the input voltage to the module.
Using this setup, I could test the
module’s performance at various output voltages for a range of output currents at each voltage level. The results
are summarised in Fig.2.
The red horizontal lines show the
module’s output current at the nine
voltage settings I used for testing: 24V,
18V, 15V, 12V, 9V, 7.5V, 5V, 3.3V and
2.5V. The dashed pink curve shows
the module’s rated maximum output
power of 3W.
An example photo
showing what the
voltage display
looks like when
powered on, here it
is supplying 15.0V.
64
Silicon Chip
Australia's electronics magazine
siliconchip.com.au
The output voltage at each setting
remained essentially constant for current levels beyond that corresponding
to 3W of output power; there was no
‘drooping’ on any of the voltage plots.
The voltage level at the 24V setting
remained within 30mV up to a load
of 200mA (4.8W!), while the level at
the 18V setting was within 45mV up
to 300mA (5.4W).
The voltage at the 15V setting
remained within 3mV at loads up to
300mA (4.5W); at the 12V setting, it
remained within 5mV at loads up to
300mA (3.6W); at the 9V setting, it
remained within 5mV at loads up to
400mA (3.6W); and at the 7.5V setting,
it remained within 25mV at loads up
to 500mA (3.75W).
Its output voltage held up similarly
well at the 5V and lower voltage settings, so you can see why the plots
in Fig.2 are all shown simply as horizontal lines.
Although I tested the module’s performance beyond the 3W limit, that
was only for brief periods. I would
not recommend using the module to
deliver more than 3W for more than
short periods to prevent it from overheating and possibly being damaged.
The next test I ran on the module
was to check the accuracy of its LED
voltage display at various output voltage settings. Here again, it performed
well, as shown in Fig.3.
The readout error was highest at
2.5V, at +1.2%, then varied between
-0.2% and +0.8% before rising to
+0.5% at 12V, then falling to -0.3%,
-0.1% at 18V and 20V, and then to
-0.6% at 24V. So, using the module’s
LED display to set its output voltage
gets you pretty close.
The error percentages provided are
best-case values, an additional error
of up to 100mV is possible due to display rounding.
Fig.2: this graph shows how the Zk-DP power supply module performed at
various voltages for different output currents.
Fig.3: this graph shows the difference between the selected output voltage and
the voltage displayed on the 3-digit segment display.
Conclusion
There is little more to say about this
tiny low-voltage voltage conversion
module. It is nicely made, performs
surprisingly well and carries a very
small price tag.
You could use it to power a small
breadboard during development from
a conveniently nearby computer, or
any other time you need a stable DC
voltage at a modest current level. Adding it to a USB power bank makes a
handy portable, adjustable DC voltage source.
SC
siliconchip.com.au
There’s nothing of importance on the underside of the module, although this is
the only place that the output polarity is clearly indicated.
Australia's electronics magazine
October 2024 65
SILICON CHIP
Mini Projects #012 – by Tim Blythman
There are lots of IoT (Internet of Things) gadgets and widgets available,
but many require a subscription to work. The WiFi Relay Remote
Control could be considered one of the simplest IoT devices. You
don’t need to sign up for anything, and you can build it yourself.
WiFi Relay
Remote Control
W
e covered Jaycar’s XC3804
WiFi Relay Module in January
2024 (siliconchip.au/Article/16088).
As the name suggests, it is a small
module containing a relay and a WiFi
radio. The Relay Module can be controlled by sending commands over a
WiFi network. It doesn’t even need an
internet connection to work.
While it’s a handy tool, another
device is required to operate it. You
could use an old mobile phone or similar WiFi-equipped device to control
it, but we think there are better ways.
So we’ve designed the WiFi Relay
Remote Control.
As the name suggests, it is a remote
controller for the Relay Module. Since
the Relay Module uses a dedicated
WiFi network for its operation, it’s
easy to set up a controller dedicated
to that task.
WiFi Relay Module
There are more details on the WiFi
Relay Module in our other article,
but the principle of operation is as
follows. The Relay Module sets up a
WiFi access point, allowing WiFi clients to connect. When it receives particular web page requests, it operates
the relay in response.
So we just need to create a client that
connects to the access point and then
sends the appropriate requests depending on user input, like pushing a button. It would be good if it also indicated if the request has worked or not.
That’s basically how the WiFi Relay
Remote works. It has two pushbuttons
connected to a WiFi Mini Main Board
that connects to the access point provided by the Relay Module. When
the buttons are pressed, it sends commands to open or close the relay.
We’ve used illuminated pushbuttons, so the LEDs light up to show
what is happening. You can see a video
showing the WiFi Relay Remote in
operation at siliconchip.au/link/abx4
Circuit details
Fig.1 shows the circuit diagram.
The pushbutton contacts are each connected between a digital I/O pin and
ground. Internally, the processor on
the WiFi Mini applies a weak pullup
Fig.1: you could easily rig it up on a breadboard if you wanted to test it before
building it. We recommend using the same pins on the D1 Mini as we did, as
some other pins have special functions that might cause a conflict.
Fig.2: how we placed
parts on the underside of
the shield (also refer to
the adjacent photo). The
shield’s top side is bare,
apart from the switches.
The wiring is hidden
on the underside of the shield. We
originally planned to use the D8
pin instead of D1, which would
have made the layout neater.
However, that is impractical, as
D8 has a pulldown instead of a
pullup.
for those pins, so it can sense when
the switch is closed and the I/O pin
is pulled to ground.
Two status LEDs are also provided
that are internal to the illuminated
pushbuttons. Each has a 220W series
resistor to limit the current flow to an
appropriate level for the LEDs. The
WiFi Mini also has an onboard LED
that lights up when pin D4 is driven
low, so we can also use that as an
indicator.
Construction
We intended the Remote to be a compact and self-contained unit, so the
hardware has been assembled onto a
small prototyping shield that can plug
into a WiFi Mini. Fig.2 and the photos
show how it has been laid out.
Start by fitting the switches.
Straighten the leads so that they will
slot straight into the prototyping
shield. To get the orientation correct,
note the longer (LED anode) pins and
place them as shown. Solder them
after making sure the switches are flat
against the shield.
Solder the two resistors as shown,
from the longer anode pin to the pads
for D6 and D7. We use the inside row
of pads so the outer rows are free for
attaching the headers later. Keep the
wire lead offcuts for the next steps.
Next, solder a wire from the D5
pad to the corner lead of the switch
as shown. All three leads on the
other side of both switches connect to
ground, so run a wire from each group
of three back to the ground (G) pin.
Then run a piece of insulated wire
from the switch with the red LED back
to D1. Slot the header pins onto the
WiFi Mini (to align them) and then
solder them to the prototyping shield.
That’s it, the hardware is finished!
Software operation
The software consists of an Arduino
sketch that uses the ESP8266 board
profile. The sketch attempts to connect
to the ‘Duinotech WiFi Relay’ access
The assembled shield
slots onto the top
of the WiFi Mini,
making for a compact
unit. We used a small
breadboard and jumper wires to
power the WiFi Relay Module
from the same supply for testing.
The switch with the red ‘off’
LED is at the top, while the
green ‘on’ LED is at the bottom.
Unfortunately, there is no way
to tell them apart when unlit,
so our software lights both
LEDs dimly so you can tell
which is which.
point created by the Relay Module,
flashing the onboard (D4) LED until
it does.
Both switch LEDs are made to light
dimly by driving them with a low duty
cycle PWM (pulse width modulated)
waveform so you can see which is on
(green) and off (red). The software
then waits until one of the buttons is
pressed and sends the corresponding
request to the Relay Module. Simultaneously, both LEDs switch off to indicate that a request is pending.
If there is a successful response, the
corresponding LED is switched on at
full brightness, and the Relay Module
will have its state set accordingly. If the
request fails, both LEDs will return to
a dim state after a while. The request
can be tried again by pushing one of
the buttons.
Firmware installation
Open the Arduino IDE and check
that you have https://arduino.esp8266.
com/stable/package_esp8266com_
index.json in your list of Board Manager URLs. Next, install the ESP8266
board profile from the Boards Manager
Parts List – WiFi Relay Remote Control (JMP012)
1 Smart WiFi Relay Main Board [Jaycar XC3804]
1 WiFi Mini Main Board [Jaycar XC3802]
1 WiFi Mini Prototyping Shield [Jaycar XC3850]
1 PCB-mounting tactile switch with integrated red LED [Jaycar SP0620]
1 PCB-mounting tactile switch with integrated green LED [Jaycar SP0621]
2 220W ½W 1% axial resistors [Jaycar RR0556]
1 25mm length of insulated wire
2 5V DC power supplies
siliconchip.com.au
Australia's electronics magazine
window. We used
version
3.1.2 of the board profile, but later versions should work too.
Download the software package for
this project from siliconchip.com.au/
Shop/6/460 and then choose the ‘D1 R2
& Mini’ board type and its corresponding serial port in the IDE. Upload the
sketch; no changes need to be made
as the Relay Module uses a fixed WiFi
network.
Operation
The LEDs on both buttons should
light up dimly and the small blue LED
on the WiFi Mini should start flashing. Power on the Relay Module. As
you can see from our video and photo
above, we just used a pair of jumper
wires connected to the WiFi Mini’s 5V
& GND (G) pins to get power for testing.
After a few seconds, the blue LED
will light solidly and you can control
the Relay Module by pressing the buttons. If the blue LED goes out at any
point, the Remote has lost its connection. In that case, check that the Relay
Module is powered correctly.
Note that other devices (such as
a mobile phone or another Remote)
can control the Relay Module. In this
case, the LEDs might not show the correct status. There is no way to get the
Relay Module’s status without triggering it, so there is no workaround for
that without reprogramming the WiFi
Relay Module with altered firmware.
Now you can set up the Relay Module to run off its own power source
and also control something.
SC
October 2024 67
Mini Projects #015 – by Tim Blythman
SILICON CHIP
Analog Servo
Gauge
A gauge with a needle is often the
simplest way of communicating a
reading. This project lets you convert
an analog voltage to a gauge readout. Because
it uses a servo motor, you can make it really big!
› Only needs a 5V DC supply
› Span and offset adjustment trimpots
› Converts a 0-5V signal into a PWM signal to drive a servo motor
› Uses just one comparator IC and a voltage regulator, plus some passives.
T
his project displays a voltage
from 0-5V using a moving needle.
While simple analog voltmeter movements can do this, they are delicate,
somewhat expensive, and limited in
size due to the movement’s strength.
Our servo motor allows a much
larger pointer to be used. That means
some extra circuitry is needed, but
our circuit uses just a few inexpensive
parts and can be built on a prototyping board in under an hour.
The servo we are using (intended
for use in remote-controlled [RC] vehicles and such) comes with mounting
screws and plastic arms (‘horns’), so it
is easy to attach it to a dial to suit your
application. Making a suitable needle
that can be affixed to the horn is also
straightforward.
This sounds like the perfect application for a small microcontroller board
like an Arduino; it would need just a
single analog input and one digital output pin. However, servo motors similar
to those we are using were invented
before microcontrollers. So we can
drive the servo motor using some
old-fashioned analog electronics.
You can see a video of the Servo
Gauge working at siliconchip.au/
Videos/Analog+Servo+Gauge
How an RC servo works
The term ‘servo motor’ has a broader
scope than just the type we are using
in this project. In general, any motor
that uses a feedback system to attain
accurate positioning can be considered
a servo motor. Specifically, we use a
standard three-wire servo, as used for
radio control (RC) and robotics.
Apart from 5V power and ground,
this type of servo has a digital input
that accepts a pulse train. The pulses
are sent around 50 times per second;
the exact rate is unimportant but the
pulse width is. Pulses around 1-2ms
are commonly used.
These servos have a shaft connected
to a potentiometer. When the servo
receives a pulse, it generates its own
pulse, the length of which depends on
the potentiometer position.
By comparing the pulse lengths, the
Some components are packed quite
closely around IC1 (as can be seen in the
lead photo), but you should be able to
squeeze them all in with some care. Note
the blue wire and two bridged pads on
the back of the PCB (circled in white).
Australia's electronics magazine
siliconchip.com.au
servo knows whether it needs to turn
clockwise, anti-clockwise or stay still
(when it has reached the desired position). Bob Young’s article in the March
1991 issue explains this in more depth
(siliconchip.au/Article/7102).
Unsurprisingly, modern servos contain a microcontroller, but they are still
compatible with the same protocol that
dates back to the 1960s. So we can easily interface with modern servo motors
using electronics of a similar age.
Circuit details
Our circuit (shown in Fig.1) consists of several simple sections with
distinct purposes. The section around
REG1 at upper right generates a stable
3.3V for the rest of the circuit from the
5V DC input.
Since the servo can draw relatively high current pulses that might
affect the 5V rail, this is necessary to
ensure the rest of the circuit does not
change its behaviour. We are using an
LM2936-3.3 regulator with the two
capacitors it requires at its input and
output.
The other two parts of the circuit
each use half of an LM393 dual comparator IC. As the name suggests, this
IC compares the voltages of its two
input pins. If the + (non-inverting)
input (pin 3 or 5) is higher than the –
(inverting) input (pin 2 or 6), the corresponding output pin (pin 1 or 7) is
not driven.
If the inverting input is higher than
the non-inverting input, the output is
pulled to ground (0V). This is known
as an ‘open collector’ or ‘open drain’
since it is usually implemented with
a transistor where the collector (or
drain) is only connected to the output pin.
The circuit around IC1a is a sawtooth waveform generator. Initially,
the 2.2µF capacitor is discharged and
the V_SAW level (and thus pin 2) is
at 0V. Around 2.2V is on pin 3, so the
output at pin 1 is not driven and thus
pulled up by the 1kW resistor.
The 2.2µF capacitor charges up via
the 1kW and 4.7kW resistors until it
reaches 2.2V, at which point the comparator output goes low. This causes
the capacitor to start discharging via
the 4.7kW resistor, into the comparator’s low output pin.
At the same time, the voltage at pin
3 goes to around 1V. When the capacitor (V_SAW) reaches 1V, the comparator output changes again and the cycle
siliconchip.com.au
Fig.1: 3.3V regulator REG1 ensures variations in the supply voltage don’t
affect the pulse timing. One half of the comparator (IC1a) provides a sawtooth
waveform, while the other half (IC1b) uses that to generate pulses suitable for
driving the servo motor.
5.0
4.0
3.0
2.0
1.0
0.0
-1.0V
-20.0ms
0.0
20.0
40.0
60.0
80.0
100.0
Scope 1: the blue trace is V_SAW (pin 5 of IC1b), green is pin 6 of IC1b, yellow/
brown is the servo control signal from pin 7 of IC1b and red is output pin 1 of
oscillator IC1a.
5.0
4.0
3.0
2.0
1.0
0.0
-1.0V
-20.0ms
0.0
20.0
40.0
60.0
80.0
100.0
Scope 2: this is the same as Scope 1 except that the green trace voltage has
changed slightly due to varying the control signal voltage, resulting in a change
in the pulse width of the yellow/brown trace that goes to the servo motor.
Australia's electronics magazine
October 2024 69
We created this simple design, printed it out and glued it to some cardboard to
suit a 5V scale over about 90°. The needle is simply a piece of dark-coloured cardboard
glued to one of the servo horns. All the necessary screws should come bundled with the motor.
Watch the polarity of the electrolytic capacitors; their negative leads all connect to the ground rail.
continues around 40 times per second.
Scope 1 shows the V_SAW voltage (the
blue trace) and the pin 2 comparator
non-inverting input (red trace).
The arrangement of resistors and
potentiometers connected to the second comparator translates the input
voltage (from the Control input) to a
voltage suitable for feeding to comparator IC1b.
The modified voltage fed into IC1’s
pin 6 is the green trace in Scope 1,
while the output to drive the servo
(from pin 7) is the yellow trace. The
stack comprising the 4.7kW resistor,
1kW potentiometer and 10kW resistor
puts the green trace just below 2.2V,
near V_SAW’s peak, so we get the brief
pulses needed to drive the servo.
The 10kW potentiometer allows us
to set how much of the Control input
signal is passed on to the rest of the
circuitry, while the 100kW resistor
ensures that the Control input only has
a small effect on the green trace level.
The 2.2µF capacitor in this part of
the circuit ensures that the control
voltage doesn’t change too rapidly. If
the voltage here jumped around too
fast, it could cause glitches that would
make the motor behave erratically or
even damage it.
Scope 1 was captured with the control input at 0V, while Scope 2 has the
control input at 5V; otherwise, the circumstances are identical. You can see
that the green trace has lifted slightly,
causing the pulse width to nearly
halve. That gives the required 1-2ms
pulse range to control the servo over
a roughly 90° range of rotation.
Construction
The first step is to build the circuit,
which can be done on a small prototyping board with a similar layout to
a breadboard (except that the power
rails are down the middle). You don’t
have to follow our layout strictly, but
we know it works, so you might find
it easier to match it.
Check our photos and the layout
diagram, Fig.2, while you solder the
components to the board and add the
Fig.2: here is how
we have laid out
the components
on a prototyping
board. Note that
there is a single
wire link under the
IC, between pins
2 and 5, shown
in cyan. The
ground and 5V
supplies for the IC
are also connected
by bridging pins 4
and 8 to their power
rails with solder
blobs.
70
Silicon Chip
wires. While most features are visible from the top of the board, a wire
and a couple of solder links are on the
underside (see the photo on the opening spread).
Start by fitting the IC socket; this will
make it easier to run some tests with
the IC out of circuit. Note the direction of the notch (to the left). Install
the parts as shown, paying attention
to the orientation of the electrolytic
capacitors.
After fitting all the components
except IC1, add the wires shown.
Three are on the copper side of the
board, under the IC1 socket. In addition to those, there are two dark grey
ground wires, two orange 3.3V power
wires and one cyan/blue signal wire;
don’t forget to add any of them.
After that, connect a 5V DC power
supply and run some tests. We used
cut-off jumper wires so that we could
plug into an Arduino board for power
but you might have a different idea.
Apply 5V and check that you get
3.3V at pin 1 of the regulator (towards
Fig.3: use this guide to help cut a
hole to suit the servo motor. It can
be copied (or downloaded and
printed) for use as a template.
Australia's electronics magazine
siliconchip.com.au
the bottom in Fig.2); you should be
able to measure different voltages of
around 2-3V at pins 1, 2 and 3 of IC1’s
socket. Pin 6 of the IC socket should
be about 2.0-2.2V.
Disconnect the power and plug IC1
into its socket, being careful not to
fold up any of the pins under its body.
Power on the circuit and connect the
servo motor to the three-way header.
It will probably run to one of its end
stops and stall. Adjust the 1kW trimpot
so that it is near the middle of its travel.
It should work backwards; that is,
turning the trimpot clockwise will
cause the servo to turn anti-clockwise.
If it is not responding, disconnect the
power to avoid damaging the servo’s
mechanism and motor, then check
your wiring.
If all is well, connect a jumper wire
from the signal input (where the blue
wire is shown in Fig.2) to 5V. You
should then be able to move the servo
by adjusting the 10kW trimpot. Again,
be careful not to allow the servo to run
against its end stops excessively.
Parts List – Servo Gauge (JMP015)
1 micro servo motor [Jaycar YM2758]
1 25-row prototyping board [Jaycar HP9570]
1 8-pin IC socket [Jaycar PI6500]
1 3-way header, 2.54mm pitch [cut from Jaycar HM3212]
2 2-way headers, 2.54mm pitch [cut from Jaycar HM3212]
1 10kW side-adjust mini trimpot [Jaycar RT4016]
1 1kW side-adjust mini trimpot [Jaycar RT4010]
1 10cm length of insulated wire
1 5V power supply (see text)
1 gauge face and needle to suit (see photos)
Semiconductors
1 LM393 dual comparator, DIP-8 (IC1) [Jaycar ZL3393]
1 LM2936-3.3 3.3V LDO voltage regulator, TO-92 (REG1) [Jaycar ZV1650]
Capacitors
1 10μF 16V radial electrolytic [Jaycar RE6066]
2 2.2μF 63V radial electrolytic [Jaycar RE6042]
1 100nF 50V multi-layer ceramic or MKT [Jaycar RM7125]
Resistors (all ¼W or ½W 1% axial)
1 100kW [Jaycar RR0620]
1 10kW [Jaycar RR0596]
2 4.7kW [Jaycar RR0588]
2 2.2kW [Jaycar RR0580]
3 1kW [Jaycar RR0572]
Turning it into a gauge
You have a bit of flexibility in choosing your gauge face and pointer. The
servo should be supplied with screws
and plastic horns for mounting.
The photos show the basic gauge we
created, with a printed piece of paper
glued to some cardboard, to show
readings from 0V to 5V. The servo will
have a usable span of just over 180°,
but we’ve gone for a more traditional
analog gauge range of about 90°.
Fig.3 shows the dimensions of the
holes for the servo, which should
help you to cut out your gauge face
to suit. There is one rectangular cutout to make plus two small holes for
self-tapping screws to retain the servo
motor. The grey-shaded circle shows
the servo shaft, which serves as the
pivot point for the Gauge.
Fig.4 shows the image we printed
to make the gauge face; it is available
as a PDF download from siliconchip.
au/Shop/11/488
For the needle, we screwed one of
the horns to the servo shaft, then glued
a pointer to it so that it pointed at the
0V marker.
Using it
To calibrate the Gauge once the glue
has set, power the circuit and connect
the voltage input to 0V (eg, ground on
the protoboard). Then adjust the 1kW
siliconchip.com.au
Fig.4: the gauge panel artwork we created shown at 90% of actual size. You can
download it as a PDF from siliconchip.au/Shop/11/488
trimpot until it points at the 0V point
on the gauge.
Next, connect the input to 5V (or
whatever your maximum will be). The
3.3V rail is another well-defined and
accurate level. Adjust the 10kW trimpot so that it points accurately for the
higher input.
Australia's electronics magazine
The two inputs interact slightly, so
switch back and forth between them a
couple of times to make minor adjustments until the Gauge is operating
accurately.
Remember that the 10kW trimpot
will slightly load the source of the
control voltage.
SC
October 2024 71
Project by Stefan Keller -Tuberg
This device will disconnect a load from its
power supply if the voltage is reversed or too
high. It also disconnects the load if it draws
current above the adjustable trip level. Its
dual-rail support means it can work with
devices like audio amplifiers with a split
(positive and negative) supply.
I
Dual-Rail
Load Protector
n June 2024, we published three DC
Supply Protectors that guard against
reversed or excessive supply voltages,
but they could only handle a single-rail
supply (siliconchip.au/Article/16292).
This design provides even more functions, extends the reverse/overvoltage protection to split rails and adds
adjustable current limits with automatic or manual resetting.
If you’ve built something that uses
flying power leads, you may already
have had a close call mixing up polarities. Or have you ever forgotten to
check that you’re using the right supply to power a device? If any of these
ring true, this design might help avoid
a catastrophe by introducing power
supply protection. It’s so versatile
that you’ll think of many applications for it.
The overvoltage cut-out levels can
be set between ±5V and ±19V (or 5-38V
for the single-rail version). If the supply overshoots the protection level,
this device will rapidly interrupt it.
The overcurrent thresholds are set
by a current sense resistor and trimpot. The sense resistance is chosen
so the voltage drop is approximately
50mV at the nominal protection level.
The trimpot range permits adjustment
from zero up to twice the nominal current level.
When the current limit is reached,
it interrupts the offending power rail
72
Silicon Chip
by turning it off completely, similar
to a fuse blowing. This minimises the
chance of damage due to a fault compared to simply holding the current
at the threshold by reducing the voltage, as a current-limited bench supply would do.
Also, if the device is unattended
when it fails, interrupting rather than
limiting the power delivered could
help avoid an even larger disaster.
It can be set so that when the overcurrent circuit trips, it will automatically reconnect after a two-second
delay or require manual intervention (a button press). If your dual-rail
application is asymmetric, you can set
different overvoltage and overcurrent
thresholds for each rail.
Depending on the Mosfets used, it
can handle up to 4-7A per rail without heatsinking. Adding heatsinks to
the Mosfets will allow them to handle
more, up to 10A for the higher-current
Mosfets specified.
Due to the design’s modularity, you
only need to populate the required
features. To start with, you can equip
it to suit single or dual supply rails.
Configuring it for a single rail saves a
few components and doubles the single supply maximum voltage to 36V.
If your device to be protected has
more than one positive or more than
Fig.1: some of the different
ways the Supply Protector
can be used. If the maximum
voltage of ±18V for the dualrail version is not enough for
your application, you can
stack two boards to double
that, as shown on the far
right.
Australia's electronics magazine
siliconchip.com.au
Features & Specifications
● Voltage range: 4-36V DC or
±4-18V DC (±4-36V DC with two
boards)
● Over-voltage cut-out: 5-38V DC
or ±5-19V DC (±5-38V DC with
two boards)
● Voltage withstand: up to ±60V
at either input or across both
inputs
● Current capability: 7A+
without heatsinking (more with
heatsinks)
● Voltage insertion loss: typically
<300mV <at> 10A
● Over-current protection:
disconnects rails independently
if current draw exceeds a set
threshold
● Over-current reset: automatically
after two seconds or manually
via pushbutton
🔹
🔹
🔹
🔹 exact values depend on parts used
one negative rail, you can common the
grounds and use two or more of these
boards to protect them all, including
dual-rail applications operating up to
±36V, as shown in Fig.1.
You can leave some components off
if you don’t need overcurrent protection. You can also leave off the overvoltage sections if you don’t want that
feature. The circuit is arranged in three
sections, each supporting one or two
power rails.
Reverse polarity protection
The first section of the circuit, shown
in Fig.2, uses Mosfets Q1 & Q2 like
‘ideal diodes’. They have a very low
voltage drop when forward-biased but
a high impedance when reverse-biased.
If you accidentally connect the input
voltages with the wrong polarity, the
internal body diodes of Mosfets Q1 and
Q2 will be reverse-biased, and no current can flow. Q1 and Q2 remain off,
protecting all the downstream components from the abnormal condition.
The specified Mosfets have reverse
voltage ratings up to 60V, offering
plenty of protection against accidental power supply reversal.
However, without protection, the
Mosfets could be damaged by gate-tosource voltages exceeding 20V. Zener
diodes ZD1 and ZD2 ensure that the
voltage between the gate and source
of each Mosfet cannot exceed 15V.
Other Mosfets in the design have similar protections.
When the input voltage polarities
are correct, the internal diodes of Q1
& Q2 are forward-biased. As current
starts to flow, 47kW resistors pull the
Mosfet gates to ground, so they switch
on. As the gate bias exceeds 2-4V and
the Mosfet channel resistance drops,
the internal protection diodes will be
shunted, so very little voltage will be
lost across the Mosfets.
The Supply Protector’s minimum
voltage rating of 4V is because that
is the minimum voltage at which the
Mosfets used are guaranteed to switch
on and conduct sufficient current.
Over-voltage protection
The following section deals with
over-voltages. Zener diodes ZD3 and
ZD6 set a fixed value for each rail’s
protection threshold. The knee voltage for 1W zener diodes rated above
5.6V occurs around 3.5-5% below the
nominal zener voltage. As the supply
voltage reaches this level, they will
start to break down. Lower voltage
zener diodes have a more rounded
knee, so the difference from nominal
can be larger.
When enough current flows to
develop 0.6V at the gate of the associated SCR, it will trigger and switch
off either Mosfet Q4, in series with the
positive rail, or Mosfet Q5 in the negative rail, disconnecting and protecting
the downstream circuitry and the load.
The SCR will remain latched until
the supply voltage is removed. Providing the applied voltage remains below
the Mosfet specification (55V or 60V),
the unit will tolerate the condition
indefinitely, and the device you’re
protecting will stay safe.
Most applications won’t require
fine overvoltage threshold adjustment,
so you can simply set it by selecting
the nearest zener. Two extra diodes
labelled D4 and D5, in series with
the zeners, allow the threshold to be
tweaked. Usually, they are replaced
with wire links, but if required, regular or schottky diodes can be fitted to
increase the overvoltage trip thresholds by 0.3V (SB140/1N5819) or 0.6V
(1N4004).
Op amp IC1 has an absolute maximum limit of 40V, the highest overvoltage threshold supported. In practice, the trip points should be no more
than ±19V for one dual-rail device or
38V for a single-rail version, giving a
small safety margin.
The 220μF and 3300μF electrolytic capacitors are to counteract the
effects of power source inductance.
At switch-on, many devices cause a
momentary current surge as the supply
Dual-Rail Load Protector hard-to-get parts (SC7366, $35): includes the PCB and all semis except the optional/varying diodes.
siliconchip.com.au
Australia's electronics magazine
October 2024 73
Fig.2: the Supply Protector circuit has mostly independent positive and negative sections with three stages each. The
first is reverse polarity protection (using Mosfets Q1 & Q2), followed by overvoltage protection (Mosfets Q4 & Q5), then
overcurrent protection (Mosfets Q10 & Q11). The only sections shared between the positive and negative rails are the
half-supply generator (IC1d), reset oscillator (IC1c) and reset switch.
bypass capacitors charge. This high
current pulse can interact with inductances in the wiring etc, causing ‘ringing’ (oscillation), which causes an overshoot voltage to appear on the affected
power rail, sometimes a significant one.
One of my test supplies caused
damped oscillations with a frequency
of around 2MHz, resulting in a peak
overshoot voltage of around 50%
above the nominal supply. This persistently tripped the overvoltage protection at power-on.
The electrolytic capacitors dampen
power-on overshoot to avoid false
overvoltage trips. In severe cases, you
may need to increase the value of the
220μF parts, although they should
be sufficient for most cases. It is usually more severe with a longer input
power cable.
Overcurrent protection
The third section of the circuit
74
Silicon Chip
provides overcurrent protection.
The load current is monitored by the
voltage drop across the ‘+sense’ and
‘-sense’ resistors. For the positive rail,
LED15, VR1 and one ‘+bias’ resistor
set an adjustable reference voltage at
pin 3 of IC1a that is a couple of volts
below the +ve rail voltage.
LED17 and the other ‘+bias’ resistor create another voltage at IC1’s pin
2 that varies with the ‘+sense’ voltage
drop. IC1a compares these voltages; its
output is low when the sensed current
is below the setpoint, so Mosfet Q10
is usually on. If the current setpoint
is exceeded, IC1a’s output goes high,
switching off Q10 and disconnecting
the load, while also lighting overcurrent indicator LED21. Op amp IC1b,
Mosfet Q11 and LED22 function similarly for the negative rail.
The purposes of LED15 and LED17
aren’t to emit light; they provide
consistent voltage drops so the op
Australia's electronics magazine
amp inputs remain within the chip’s
common-
mode range, which does
not go up to the positive rail. The fact
that LEDs have a higher voltage drop
than a regular silicon diode (around
1.8V rather than 0.7V) is useful in this
application.
The voltage across the ‘+sense’ resistors is approximately 50mV at the
nominal overcurrent trip point. VR1 is
for fine-tuning; its 100W value means
that with 1mA flowing through it, a
full trimpot rotation will cover twice
the nominal voltage range expected
across ‘+sense’.
Note that the ‘+set’ LED (LED15)
usually goes out when the overcurrent
LED (LED21) lights. However, there
are cases where the current is near the
overcurrent set point where both could
light. So if you notice that, it’s normal.
The overcurrent protection only
interrupts the rail experiencing the
overload. When that happens for the
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positive rail, D19 provides a feedback
path to latch the state even after Q10
interrupts the current and the ‘+sense’
voltage drop falls back to zero. It will
remain off until the condition is reset
by NPN transistor Q8 switching on
and pulling pin 3 of IC1a below the
pin 2 level.
When the output of IC1a goes high,
another NPN transistor (Q9) inverts
the transition to create a falling edge.
This is combined with any falling edge
from IC1b by diode D24. These are
AC-coupled to IC1c by a 1nF capacitor and diode D29, which works as
an overcurrent reset monostable. A
two-second delay is provided by the
1μF capacitor and 2.2MW resistor. The
100kΩ resistor at pin 9 of IC1c prevents
damaging input currents when pins 9
and 10 differ by more than 5.5V.
When the monostable times out (if
enabled) or the reset pushbutton is
pressed, Q6, Q7 and Q8 temporarily
siliconchip.com.au
shift the voltage levels at the inputs of
IC1a and IC1b. This forces them out of
their latched states, re-enabling Mosfets Q10 and Q11.
If the auto-reset feature is enabled,
voltage to the load will be restored
two seconds after it trips. If the overcurrent condition persists, the trigger-
delay-restore process will repeat indefinitely every two seconds (or until the
fault clears).
This monostable arrangement
requires a reference voltage at the
midpoint of the IC’s power supply.
We could have used the GND line for
this reference, but that would mean
the circuit would only work with symmetrical dual rails, reducing its flexibility. So IC1d synthesises a mid-rail
voltage (halfway between +ve and -ve)
that self-adjusts without needing different configurations.
The 100nF capacitor and 1MW resistor connected to header CON3 ensure
Australia's electronics magazine
that resets are only momentary, even
if the pushbutton is held down. This
quickly rearms the overcurrent protection while preventing the output
from being held on continuously if
excessive current continues to flow.
The 100nF capacitor at IC1c’s output works similarly for monostable-
initiated resets.
We don’t care about the brightness
of LED15-LED18 since, as mentioned,
they are not indicators. However, it
does matter for LED7, LED8, LED21
and LED22. The circuit shows 22kW
current limiting resistors for them,
suiting high-brightness LEDs. If using
regular LEDs, reduce the values to
around 5.6kW for more current.
Alternatively, if they’re too bright
(which may happen with higher-
voltage single-rail applications),
increase the series resistances.
Diodes D26 and D27 across the
output terminals are normally
October 2024 75
reverse-biased. These protect the circuit from inductive loads or long output power leads. Any inductance in
these can cause a reverse voltage spike
when the load current is interrupted
(as can certain capacitor configurations in the load). These diodes will
safely dissipate that energy.
Component selection
The PCB is designed for miniature
1/8W resistors, 3.5mm long. You can
get them from element14, DigiKey or
Mouser. You can use more common
1/4W resistors, but you will need to
stand them up (at least partially).
The current sense resistors will
typically be below 0.1W. element14,
DigiKey and Mouser have wide ranges
of low-value ‘current sense’ resistors,
many of which will be suitable, even
if their power ratings are higher than
necessary. Alternatively, parallel two
or more resistors to create a lower resistance. The PCB holes are large enough
for the leads of current-sense resistors
or multiple regular resistors.
The parts list gives information
on supported capacitor lead pitches
(although you can bend them if you
have to) and suggested Mosfet types.
However, many more suitable ones
will be available.
If substituting other Mosfets, pay
particular attention to their maximum
on-resistance, Vgs threshold voltage and reverse breakdown voltage.
Particularly for P-channel Mosfets,
cost-effective options with a low on-
resistance aren’t common. The higher
the maximum on-resistance, the hotter
the Mosfets will run.
Heatsinking
Using, say, IRF1018E and IRF4905
Mosfets, at 4A current draw and 10V
or higher, they will dissipate 135mW
and 320mW each, respectively. The
temperature of a TO-220 package in
free air rises by around 70°C/W, so
without heatsinking, they will rise to
9°C and 22°C above ambient.
Note that the ambient temperature is
the air temperature within the enclosure, which could be significantly
higher than room temperature.
The Mosfet on-resistances could be
a little higher when using rail voltages
significantly below 10V, so for lower
operating voltages, pay close attention
to the Mosfet temperatures during testing. If they become too warm to touch
comfortably, they require heatsinks.
If you know or suspect you’ll need
heatsinks in advance, it will be easiest
to fabricate and mount the transistors
onto them before soldering the transistors to the PCB.
You can fashion heatsinks from
3mm aluminium using three separate
bars or angles for the three rows of
Mosfets. Cut the material to fit comfortably within the component footprint.
For a dual rail application, mount two
Mosfets per angle with their centre
holes spaced 18mm apart. Use insulators and Nylon bushes and/or screws;
insulating each Mosfet from its heatsink is the best practice.
You won’t necessarily require large
heatsinks; it depends on how much
power needs to be dissipated. For maximum heat dissipation, bridge the tops
of the three aluminium angles with a
commercial heatsink.
Construction
Figs.3 & 4: the dual-rail version of the Supply Protector uses all the parts on
the PCB, although some sections can be omitted. Parts that can be left off if you
don’t need over-current protection are shown, in Figs.7 & 8. Soldering heavyduty 1mm2 wires to the underside of the board, as shown here, will reduce
the resistance of the current-carrying tracks. That will lower the voltage drop
between the input and output and allow the PCB to handle more than 5A.
76
Silicon Chip
Australia's electronics magazine
Start by selecting the values of the
current sense and bias resistors, and
over-voltage threshold zeners, using
either the panel or Tables 1 & 2 overleaf.
The Supply Protector is built on a
double-sided 96 × 69mm PCB coded
18109241. If you’re building the full
dual-rail version, fit all the components shown in Fig.3, while if you
want to make the single-rail version,
fit just the components shown in Fig.5
or Fig.6. Figs.7 & 8 show further variations, which experienced constructors
siliconchip.com.au
could combine with one of the single-
rail variants if desired.
The two adjustment diodes, D4 and
D5, are generally not required and can
be replaced with wire links. If you
need to fine-tune the trip voltage, you
can fit diodes instead, as explained
earlier.
We suggest constructing in two
stages: build and test the reverse-
polarity and overvoltage protection
sections before adding the remaining
components. Roughly speaking, the
reverse and overvoltage protection
components are below and to the left
of the 3300μF electrolytic capacitor in
the middle of the board, not including
the two 3300μF capacitors (use Fig.7
as a guide).
Pay close attention to the orientation of the transistors, diodes, LEDs
and electrolytic capacitors. The two
SCRs should face in opposite direc- The fully assembled Dual Rail Supply Protector PCB with all features available.
tions. Start by fitting the lower-profile Note the use of smaller-than-usual resistors to keep it compact.
components like the diodes and resistors that will lie flat on the board (see
Figs.5 & 6:
Table 3), then the capacitors, then the
these overlay
taller components like the Mosfets.
diagrams
shows the
If you want to minimise the voltboard fitted
age drop across the device, or will be
with just the
using it at high currents, you can solder
components
extra wires to the underside as shown
needed for
in Fig.4. That should not be necessary
a single
for applications up to around 5A per
rail Supply
rail, though.
Protector.
You need
to add wire
links where
shown in
red. When
building
any of these
versions,
watch the
orientation of
the IC, diodes
and Mosfets,
as they must
all be correct.
Initial testing
The easiest way to verify the correct
operation of the reverse polarity protection is with a variable power supply. Apply power to the input connector in reverse but starting at 0V. Ramp
the voltage slowly up to -1V and monitor the “+rail” and “–rail” test points
with a multimeter to verify the absence
of any voltage. It is working if the supply reaches -1V and there is no voltage
on those test points.
You could use one AA or AAA cell
if you don’t have a variable power
supply.
Note that if you previously applied
power in the correct direction, your
multimeter may read the residual
charge on the 220μF capacitors.
Next, verify the overvoltage protection threshold by switching off the
variable power supply and reconnecting the supply with the correct polarity. As you ramp the variable power
supply up, by the time it reaches 1V,
a voltage will be detectable on both
test points.
siliconchip.com.au
Australia's electronics magazine
October 2024 77
Pluggable terminal blocks for the inputs
and outputs make connecting the wires easy.
The board can be mounted using a tapped
spacer in each corner.
Figs.7 & 8:
these
overlays
shows which
components
you can
leave off (or
link out) if
you don’t
want either
the overcurrent or
over-voltage
protection
feature. If
building a
single-rail
version, you
will need to
refer to Figs.5
& 6 as well,
and figure
out which
components
to leave off or
link out.
78
Silicon Chip
Australia's electronics magazine
The readings will initially be around
0.7V below the variable power supply level. Once you reach 3-4V, the
test point voltages should rise to the
input voltage.
There are two additional test points
labelled “+rail prot” and “–rail prot”,
which you can now monitor. Continue
increasing the variable supply towards
the protection threshold. As you pass
the threshold, each overvoltage protection LED should illuminate and
then, at a fractionally higher input
voltage, the “+rail prot” and “-rail
prot” test points should start falling
back to zero.
The actual tripping thresholds may
differ from the calculated value due to
component tolerances and the zener
knees.
Remember not to ramp the input
voltage past the ratings of the 220μF
capacitors, and be very careful not to
ramp your variable supply past 40V (or
±20V) until you are sure the overvoltage protection in both rails is working
correctly, or you risk damaging IC1 (if
fitted). If either rail’s protection hasn’t
kicked in by 1V beyond the calculated
trip point, it’s either not working, or
the zeners are wrong.
To reset after the overvoltage protection has tripped, return the variable supply to 0V or temporarily disconnect it.
With the overvoltage protection section working, you can finish fitting
components to the PCB, starting with
IC1; ensure its pin 1 indicator goes at
upper right as shown in the overlay
diagram. Don’t mount the two trimpots yet.
If your board needs cleaning because
it’s covered in flux residue, submerge
it under isopropyl alcohol or methylated spirits and gently rub it with an
old toothbrush. Wait for it to dry, then
mount and solder the trimpots.
Check that Mosfets are electrically
isolated from any heatsink metal.
To verify the overcurrent trip circuit,
connect the power rail (or rails) to a
variable supply but don’t yet connect
a load. Adjust the power supply to the
same voltage you used to calculate
the bias resistances. If either overcurrent trip LED is already illuminated,
slowly wind the trimpots clockwise
until they extinguish automatically,
use the pushbutton reset or short the
upper two pins of CON3.
If either of the overcurrent trip LEDs
fails to extinguish, there is a problem
siliconchip.com.au
with the reset or overcurrent circuit.
If you’re using auto-reset, check the
output of IC1d at the “VG” (virtual
ground) test point is near ground level
for a symmetrical dual-rail version,
or otherwise approximately midway
between the power rails.
Assuming both overcurrent LEDs
are off and the set LEDs are on,
wind each trimpot anti-clockwise
until either the trimpot is fully anti-
clockwise or the corresponding set
LED switches off and the overcurrent
LED comes on. When you’ve reached
this point, nudge the trimpot clockwise (and press the reset button if
equipped) so both the overcurrent
LEDs are again off.
The overcurrent protection circuits
will now be armed at a very small current threshold. Use a low-value resistor (say 100W or less) between ground
and each output rail to verify that
the overcurrent protection triggers.
The corresponding overcurrent LED
should illuminate instantaneously,
and the associated set LED should
extinguish.
If your overcurrent trip point
exceeds the normal operating current by an amp or more, connect a
dummy load that will draw current
just below the overcurrent tripping
point and adjust VR1 and VR2 so the
load remains turned on. Otherwise,
use your intended load to set the overcurrent trip point.
Finally, run the device for ten minutes while monitoring the temperature
of the Mosfets. If the Mosfets become
too warm to touch comfortably, turn
off the power and fit heatsinks before
using it. Wire it up, and you can sit
back and relax, knowing your load
device is protected!
Parts List – DC Supply Protectors (all features)
1 double-sided PCB coded 18109241, 96 × 69mm
2 100W miniature top-adjust trimpots (VR1, VR2)
2 3-way 5.08mm pitch pluggable terminal blocks (CON1, CON2)
[Jaycar HM3113+HM3123, Altronics P2873+P2813]
1 3-way pin header and jumper shunt (CON3)
1 NO momentary pushbutton (optional)
4 M3 × 6mm panhead machine screws and matching spacers
Semiconductors
1 NCS20074 quad rail-to-rail output op amp, SOIC-14 (IC1)
3 high-current P-channel Mosfets, TO-220 (Q1, Q4, Q10) ★
3 high-current N-channel Mosfets, TO-220 (Q2, Q5, Q11) ★
2 BC556 45V 100mA PNP transistors, TO-92 (Q3, Q7)
3 BC546 45V 100mA NPN transistors, TO-92 (Q6, Q8, Q9)
2 C106 SCRs, TO-126 (Q12, Q13)
8 high-brightness 3mm LEDs (LED7-8, LED15-18, LED21-22)
[Vishay TLLK4401]
6 15V 1A zener diodes, DO-41 (ZD1, ZD2, ZD11, ZD12, ZD23, ZD25)
2 1A zener diodes, DO-41, values to suit application – see Table 1 (ZD3, ZD6)
2 1N5819 or SB140 40V 1A schottky diodes (D13 & D14)
6 1N4148 75V 200mA diodes, DO-35 (D19-D20, D24, D28-D30)
2 1N4004 400V 1A diodes, DO-41 (D26, D27)
2 extra diodes to fine-tune over-voltage thresholds (D4, D5; optional, see text)
★ suitable types include IRF4905 (up to ±55V & 4A),
IPP80P03P4L-07 (±30V & 7A) and SUP90P06-09L-E3 (±60V & 7A)
★ suitable types include IRF1018E (7A), CSD18534KCS (7A), DIT050N06 (4A),
STP60NF06 (5A) & IPP80N06S4L (8A; all can handle up to ±60V,
ratings are without heatsinks and are only a guide)
Capacitors
2 3300μF 50V electrolytic (5mm or 7.5mm lead pitch) [Altronics R5217]
2 220μF 63V low-ESR electrolytic (3.5mm or 5mm lead pitch)
1 1μF 50V ceramic or MKT
9 100nF 50V ceramic or MKT
2 10nF 50V ceramic or MKT
1 1nF 50V ceramic or MKT
Resistors (all ⅛W 5% miniature axial unless noted) ♦
1 2.2MW
9 47kW
4 3.3kW 1W 5%
3 1MW
9 22kW
2 910W
1 330kW
1 15kW
4 Rbias resistors – see Table 1
2 150kW
6 10kW
2 Rsense resistors – see Table 2
3 100kW
♦ regular ¼W resistors can be used but they won’t sit flat on the PCB
Table 1 – zener diode values
Table 2 – current sense resistors
Trip
ZD3/ZD6 Bias resistors
Adjustment range
Sense resistor
~5V
5.1V
3.0kW
0-1A
100mW 1/8W
~5.5V
5.6V
3.3kW
0-2A
50mW 1/4W
~7.25V
6.8V
5.1kW
0-3A
33mW 1/4W
~10.3V
10V
8.2kW
0-4A
25mW 1/2W
~13V
13V
11kW
0-6A
16mW 1/2W
~15.1V
15V
13kW
0-8A
12mW 2/3W
~18V
18V
16kW
0-10A
10mW 1W
~20V
20V
18kW
~23.8V
24V
22kW
~29.5V
30V
27kW
Tables 1, 2 and the panel on the next
page are used to determine the best
values of various components to suit
your needs.
~38V
39V
36kW
siliconchip.com.au
Australia's electronics magazine
Table 3 – resistor colour codes
October 2024 79
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Calculating component values
Several component values should be selected to suit your application as follows.
Overvoltage trip point
First, you must determine the highest voltage that’s safe to apply to the load. If
unsure, measure the output of the existing power supply and add a safety margin.
Zener diodes ZD3 (‘+OVtrip’) and ZD6 (-OVtrip’) set the overvoltage trip point for
each rail in combination with the 3.3kW resistors. The SCRs will trip when their trigger input reaches approximately 0.6V. Allowing for a voltage drop of about 100mV
across the resistors, the required zener voltage is (Trip – 0.7V) × 1.05.
As mentioned earlier, low-voltage zeners may trigger at lower voltages than
expected. Also, typical zeners diodes have 5% tolerances.
In the middle of the voltage range (eg, around ±15V), you can generally get away
with a zener diode that has a voltage rating close to the desired trip point, as the
0.7V and 5% factors cancel out.
Because the expected overvoltage trip point lies within a range, and zeners are
only available in certain preferred values, you may need to use adjustment diodes
if you require high precision. Adding a schottky diode for D4 or D5 (like a BAT85,
SB140 or 1N5819) will increase that rail’s trip point by around 0.3V, while adding a
silicon diode (like a 1N4148 or 1N4004) will increase it by around 0.6V.
Don’t use zeners below 4.3V or above 19V (for a dual-rail configuration) or 39V
(for single-rail operation). You can use different values for the two zeners for asymmetric applications.
Ensure that the 3300μF output capacitors have voltage ratings above the trip
points. For example, if you have ±18.1V overvoltage protection thresholds, select
25V capacitors.
Because the 220μF capacitors after Mosfets Q1 & Q2 are on the unprotected
side of the overvoltage protection circuit, they will experience any overvoltage, so
their voltage ratings should exceed the highest expected input voltage. We recommend using 50V or 63V rated capacitors there, although you might get away
with 35V caps in some cases.
Overcurrent trip point
The ‘+sense’ and ‘-sense’ resistors are used to monitor the current in each rail.
The overcurrent trip is calculated for a sense resistor voltage drop of about 50mV,
although the trimpots let you set it up to 100mV.
Use Ohm’s law, R = V/I, and the power formula, P = VI, to calculate the required
resistances and power ratings. Let’s use 2A as an example. For a 50mV drop, the
formulas give R = 25mW (0.05V ÷ 2A). If you can’t find a resistor with the calculated value, round the resistance to the closest available value. A 0.022W, 0.025W
or 0.033W resistor would be suitable in this case.
We calculate the power at 100mV as we don’t want the resistor to overheat if the
trimpot is set to maximum, so P = 200mW (0.1V × 2A). Ideally, the resistor should
have close to twice the power rating (to account for elevated ambient temperatures etc), so in this case, use a ½W or 0.6W resistor.
If your application has asymmetric current requirements, you can choose different values for the two resistors.
WWW.SILICONCHIP.COM.
AU/SHOP/DIGITAL_PDFS
Bias resistances
Four resistors are labelled ‘+bias’ or ‘-bias’. The bias resistors are selected so
that about 1mA flows through them when the supply is at its nominal (not overvoltage trip) level.
The series LEDs have a forward voltage drop of around 1.8-2V, so consider that
when calculating the resistor values. The exact drop doesn’t matter as long as the
four LEDs (LED15-LED18) are the same type, so the voltage drops are similar. Red,
orange or yellow LEDs with a forward voltage drop below 2.3V will work.
You can measure the LED’s forward-biased drop using a digital multimeter’s
diode testing function.
Say the nominal power supply is ±12V and you have red LEDs with a 1.6V forward voltage. The required resistance will be R = (12V – 1.6V) ÷ 0.001A = 10.4kW.
Choose the nearest available resistance, 10kW in this case.
If you have an application with asymmetric voltage rails, the ‘+bias’ and ‘-bias’
SC
resistances may differ.
80
Australia's electronics magazine
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MICROMITE
EXPLORE-40
A wealth of software has been written for the Micromite;
The Back Shed online forum is a great place to find much
of it. This compact Explore-40 board is a Micromite
in the same form factor as the popular Pico boards,
allowing a Micromite to be used with hardware
designed for the Pico.
PROJECT BY TIM BLYTHMAN
T
HE RASPBERRY PI PICO has taken a
well-deserved place as one of the
most popular microcontroller
boards. It is cheap, easy to use and can
be programmed in C, BASIC, Micro
Python & even with the Arduino IDE.
Our Pico BackPack (March 2022;
siliconchip.au/Article/15236) capitalised on those features, providing stereo audio and a microSD card interface
with the 3.5in LCD panel that we had
previously used with the Micromite
V3 BackPack.
These new features can now be
accessed from Micromite BASIC, since
the Explore-40 board allows a Micromite processor to be plugged into the
Pico BackPack. Thanks in part to the
ongoing work of The Back Shed forum
members, software is available to use
these new features.
The Micromite Explore-40 is not just
a Micromite/PIC32 breakout board. It
has been designed to include niceties
like an inbuilt USB-serial converter,
plus some LEDs and pushbuttons. It
can even plug into a Pico Digital Video
Terminal (March & April 2024 issues;
siliconchip.au/Series/413).
Since this board is patterned after
the Raspberry Pi Pico and thus a bit
larger than the Explore-28, we have
taken the opportunity to add some
extra features.
Circuit details
Fig.1 shows the circuit of the
Explore-40. IC1 is a PIC32MX170F256B
in a relatively large 28-pin SOIC package. This is the familiar 28-pin part
The Explore-40
we have used for many Micromite
The Explore-40 is typical of min- projects.
imal Micromite implementations
Its I/O pins are connected to pins on
that include the Microbridge USB- the pair of 20-way headers that match
serial converter. The circuit resem- the pinout of the Pico. We’ll explain
bles earlier Micromite boards like the our choices for this specific mapping a
Explore-28 from the September 2019 bit later. As the Pico has more pins than
issue (siliconchip.au/Article/11914).
the 28-pin PIC32, there are some empty
positions on those 20-way headers.
IC2 is a PIC16F1455 programmed
Micromite Explore-40 Features & Specifications
with the Microbridge firmware. The
» Allows a PIC32 Micromite processor to be plugged into a Pico socket
Microbridge was originally published
» All 28-pin Micromite I/O pins are available
as a separate board (see May 2017;
» Onboard Microbridge serial interface/programmer
siliconchip.au/Article/10648); it has
» USB-C socket for power and data
since been incorporated into many
Micromite designs. It can function as
» Micromite BASIC software examples for all Pico BackPack features
a USB-serial converter, allowing com» Supports LCD touch panel with backlight control
munication between a computer and
» Supports IR receiver
the Micromite chip.
» Stereo audio output
The Microbridge can also act as a
» microSD card interface
programmer, allowing new firmware
» Realtime clock interface
(such as a new version of Micromite
» Add-on 3.5mm board provides 3.5mm stereo audio socket with Pico BackPack
BASIC) to be easily installed on the
Micromite chip.
» Power and status LEDs
As such, it connects to the data lines
» Reset and Mode pushbuttons
on USB-C connector CON1, as well
» In-circuit serial programming (ICSP) header for the PIC32 Micromite chip
as the serial and programming pins
82
Silicon Chip
Australia's electronics magazine
siliconchip.com.au
of IC1. IC2 also drives LED1, which
indicates its mode (USB-serial or
programming) and shows serial traffic. Onboard pushbutton S2 selects
IC2’s mode.
CON1, the USB-C socket, has connections to power via the VBUS pins.
The CC1 and CC2 pins are connected to
ground via 5.1kW resistors, signalling
to the USB source (eg, a computer) that
it should supply 5V on the VBUS pins.
The VBUS voltage goes via schottky
diode D1 to REG1, an MCP1700 3.3V
low-dropout regulator. The diode also
connects to pins 40 and 39 of the Pico
headers, emulating that handy feature of the Pico boards. It means that
an alternative source of 5V power
can be fed into pin 39 (possibly via
another diode) without any risk of
back-feeding the USB power supply.
REG1 and its capacitors provide
a 3.3V rail that powers IC1, IC2 and
power indicator LED2 (the latter via
a 1kW resistor). The 3.3V output is
also available on pins 35 and 36 of the
headers, as it is on the Pico boards.
IC1’s pin 1 (the MCLR reset input)
has also been taken to pin 30 (RUN
on the Pico).
Pins 3, 8, 13, 18, 23, 28, 33 and 38 of
the headers are connected to ground,
like the Pico, and we have connected
as many of the PIC32’s I/O pins as we
can to the remaining I/O pins on the
headers. Because of this compatibility, we’re sure readers will find the
Explore-40 handy in other situations
where a Pico might be used.
IC1’s MCLR reset pin, 3.3V, ground
and the two ICSP programming pins
are also available at the CON2 ICSP
header, allowing the chip to be programmed by an external programmer. IC1 can also be reset by pressing
S1, which pulls MCLR to ground. A
10kW resistor pulls this up otherwise.
A reset button is one feature that the
real Pico lacks!
Micromite Explore-40 Kit (SC6991, $35)
A complete kit is available for the Micromite Explore-40 with all the parts
listed in the parts list on page 87 (not including the Audio Breakout Board
or Pico BackPack).
Pin mapping
The mapping of the 40-pin header
has been mostly chosen to match the
functions of the Pico BackPack to that
of the Micromite. For example, the
Micromite has fixed SPI and I2C pins,
so the mapping matches the wiring
of these two peripherals on the Pico
BackPack.
Similarly, the pins for interfacing
with the LCD on the V3 BackPack
have been arranged identically on
the Explore-40. This allows identical
siliconchip.com.au
Fig.1: the Explore-40 has much in common with the Micromite V2 BackPack
and the Explore-28, although we’ve added a USB-C socket, power indicator LED
and a reset button. The I/O pin mapping to the two 20-pin headers is designed to
allow the Micromite processor to work with the Pico BackPack and retain some
compatibility with software designed for the V3 BackPack.
Australia's electronics magazine
October 2024 83
Micromite OPTIONs to be used. The
IR pin (Micromite pin 16) has also
been connected to the IR receiver on
the Pico BackPack.
Pins 21 and 22 on the Micromite
have been connected to pins 11 and
12 of the Pico header; these are used
for audio on the Pico BackPack and are
a convenient pair for this purpose. If
not used for audio, they can be used
as the Micromite’s COM1 serial port.
The serial console pins have been
allocated to pins 1 and 2, allowing the
console to be connected to the Pico
Digital Video Terminal. That doesn’t
leave many pins spare to be allocated.
We have connected pins with analog
functions where possible, although
the Pico has fewer than the Micromite.
We’ll detail the OPTIONs and pins
that should be used with the Pico BackPack later, when we explain the software features in more detail.
A small add-on
While putting together this design,
A 3.5mm jack socket breakout board for the Pico BackPack
Building this board is simple, as you can see from our photos. As long as you connect
the R, G and L pins to the matching pins on CON3 of the Pico BackPack, the board can
be installed in a few different ways.
It can be mounted on either side of the board, giving four main configurations. We
think the method shown in our photos is the simplest, gives a compact result and does
not put the audio socket awkwardly close to the microSD card socket.
The Audio Breakout extends slightly beyond the Pico BackPack and is intended to
sit just inside a UB3 Jiffy box so that the socket can be accessed through a small hole
in the side.
We suggest fitting the audio socket to the PCB first. That will allow you to easily
check that your chosen positioning does not foul any other components. The photo
shows the assembly of the listed parts that can then be fitted
to the Pico BackPack.
Once fitted, you can simply plug in headphones or an
aux cord to hear audio from CON3 on the Pico BackPack.
This is the
recommended
placement of the 3.5mm
jack socket breakout board on
the Pico BackPack, sitting above
some passive components in
the audio section. Although it’s
designed to work with the Pico
BackPack, you can also use it for
breadboarding or prototyping.
Silicon Chip
Programming the chips
IC1 can easily be programmed via
IC2 once you have built the board,
but IC2 is best programmed before it
is soldered to the board, especially as
there is no ICSP header for it.
It is possible to use a Micromite to
program a Microbridge; there are notes
on how to do that included with the
Microbridge firmware at siliconchip.
au/Shop/6/4269
Still, it is easier to program IC2 with
something like a PICkit or SNAP if you
have an appropriate SMD adaptor, so
we recommend doing that if possible.
If you buy a kit from us, both ICs will
be programmed already; there is also
the option to buy programmed chips
separately.
Construction
The Explore-40 uses mainly SMD
parts, including SOIC ICs, M2012
(0805 imperial) passive components
measuring 2.0 × 1.2mm, and a somewhat fine-pitch USB-C socket. It is
not super difficult, but neither is it
extremely easy; it would be ideal
to have some SMD soldering experience before assembling it. There
are also components on both sides
of the PCB.
You will need the usual SMD tools
and consumables. A fine- or medium-
tipped soldering iron, solder, flux
paste, tweezers and good ventilation
are essential. Some solder-wicking
braid and a means of securing the PCB
are also advised. Blu-Tack will do the
job if you don’t have a PCB vice.
You should also have a suitable solvent for cleaning up flux, such as one
recommended by your flux supplier.
Fig.2 (below): when assembling
the breakout board, ensure the
socket is pushed firmly against
the PCB. We used straight
headers, but you could use rightangled headers.
84
we realised adding a 3.5mm audio
output jack socket to the Pico BackPack would be a nice touch. We initially omitted this from the Pico BackPack because the board is quite tight
for space.
To solve this, we’ve designed a very
small daughterboard that can be connected to the Pico BackPack, breaking
out the CON3 audio connector into a
3.5mm stereo socket. It is shown in
Fig.2.
You don’t need to use the Explore-40
to use the daughterboard; it can also be
used with a Pico or Pico W. You can see
it in our photos, mounted above the
Pico BackPack PCB. We have a panel
showing how to build this board and
add it to the Pico BackPack.
Australia's electronics magazine
siliconchip.com.au
Alternatively, isopropyl alcohol or
methylated spirits will be effective
for most fluxes. Fig.3 shows the PCB
overlays, which you should refer to
during assembly.
Start by soldering CON1, the USB-C
socket, since it has the closest pin
pitch. It will also be difficult to get to
once other components are installed.
Apply flux to the pads and slot the
socket into its holes on the top of the
PCB. Clean the iron’s tip and add a
small amount of fresh solder.
The end-most leads are a bit wider,
so tack one of those in place, then
check that the other leads are aligned
to their pads and that the part is flat
against the PCB. Adjust it until you
are satisfied. The locating posts should
help here.
You can then solder the mounting
pins from the reverse of the PCB. It
might help to add some flux to the bottom and top of those pins to help the
solder take. Try not to add too much
solder to the mounting pins, as it might
get in the way later.
Next, solder the remaining pins of
CON1 on the top of the PCB. Use the
braid and extra flux to remove any
bridges that have formed. Place the
braid on the solder, apply the iron and
gently move both away together once
the solder has been taken up.
Fit the two ICs next, being sure to
get the correct orientation. IC2 faces
the opposite direction to IC1 and is
on the opposite side of the PCB. Add
flux to the PCB, rest the ICs in place
and tack one lead before soldering the
others. Adding flux to the pins before
soldering will help it flow. Check for
bridges after soldering and remove
any with more flux paste and the solder wick.
Regulator REG1 mounts on the same
side as IC2. It’s easy enough to solder
but small enough to lose sight of easily.
Add some flux and place it as shown.
Tack one lead, then check the alignment of the others before soldering.
The diode mounts on the opposite side of the board from the USB-C
socket. Ensure that the PCB’s cathode
mark matches the diode orientation
and avoid bridging its pads to the socket’s mounting pins.
Now solder the remaining parts on
the underside of the PCB methodically. The resistors will have small
codes printed on top (per the parts list)
but the capacitors will be unmarked.
You may be able to tell them apart by
siliconchip.com.au
Fig.3: we’ve placed components
on both sides of the PCB to best
use the available space. The
CON1 USB-C socket and the
two microcontrollers have the
tightest pin pitches, so they
should be fitted first. Avoid
using too much solder for
CON1 through-hole mounting
pins in case it bridges to D1
or the nearby resistors. This
diagram is shown at 150% of
actual size for clarity.
their thickness if you manage
to get them mixed up. In each
case, add flux to the pads, rest
the part in place, tack one lead,
then check and solder the other.
Next come the two LEDs on
the top side of the board. We
recommend using red for LED1
(MODE) and green for LED2 (POWER),
although you could choose your own
scheme. You can test the colour and
polarity of the LEDs with a multimeter set to diode mode.
The cathode will be the end connected to the black multimeter lead
when the LED lights up. Fit the LEDs
with the cathodes towards the COM2
silkscreen marking (the overlay also
shows a K near each cathode).
Solder the last 1kW resistor and
100nF capacitor. Clean both sides of
the PCB thoroughly with your chosen
flux solvent and allow the PCB to dry.
It’s then a good time to inspect the soldering for any bridges or dry joints you
might have missed. If you find any, fix
them before proceeding.
Fit the two tactile switches next.
They have much larger pads, making
them easier to solder than the other
parts. Your board should look like the
photos now.
If something is not right, check for
5V at the USB pin, at upper right, and
around 4.7V (due to the diode) at the
SYS pin below it. Check the USB-C
socket and 5.1kW resistors if the USB
voltage is absent. An absence of voltage at the SYS pin suggests the diode
is reversed or not connected, while a
lack of 3.3V could point to a problem
with the regulator or a short circuit on
the 3.3V rail.
If you need to fit the CON2 ICSP
header to program IC1, do that now.
Be aware that you may not be able
to leave CON2 attached afterwards
since it might be too tall to fit between
the Pico BackPack PCB and the LCD
Testing
There are still some parts to fit, but
now is a good time to do some initial tests. Connecting USB power to
CON1 should cause LED2 to light up.
The 3.3V pin should measure between
3.2V and 3.4V relative to ground.
Pressing S2 should cause LED1 to
light up, assuming IC2 is programmed
correctly.
The Explore-40 is a compact board (51
× 21mm) that allows the Micromite to
substitute for a Raspberry Pi Pico in some
circumstances. IC1 and the two LEDs are
the polarised components on the top of
the PCB. We recommend using red for
LED1 and green for LED2.
Australia's electronics magazine
85
fitting the Explore-40 to a Pico BackPack with an LCD panel above. If you
just plan to use it on a breadboard, for
example, you just need to be sure that
the pins align with the sockets in the
breadboard.
using socket headers fitted to the top
of the Explore-40 that will mate with
pin headers mounted on the underside
of the Pico BackPack.
Software support
Combining the Explore-40 with the
Pico BackPack (and 3.5in LCD panel)
For our prototype, we used low- brings two new features that were
profile header sockets and removed the not present on the V3 Micromite LCD
plastic shroud from the pin headers to BackPack. These are the microSD card
allow the board to be swapped (eg, for and audio output.
a Pico) if needed. However, we found
First we’ll recap the features that are
that quite fiddly to achieve.
shared with the Micromite V3 BackAs you can see in the photo below, Pack and how they are configured
there is very little clearance above the and used. This will be a quick way to
Explore-40, even though we removed check that the Explore-40 is working
the SD card socket from the LCD panel as expected.
above. Still, that is an option to conThese features should all behave
sider since there is no connection to identically to a Micromite V3 Backthe SD socket on the LCD panel from Pack. Note, though, that the Explore-40
the Pico BackPack.
and Pico BackPack lack the RAM or
If you want to do that, use a pair of FLASH IC and temperature sensors
flush nippers to gently cut and detach that the V3 BackPack includes.
each pin from the SD card socket, then
The Micromite firmware does not
use a soldering iron to remove the rem- have a built-in driver for the 3.5in
nants of each pin. Follow with some LCDs, but there is a loadable driver
solder-wicking braid and flux paste to developed by Peter Mather. We have
remove any solder residue.
customised this to suit the configIf you are happy to permanently sol- uration of the Explore-40 and Pico
der the Explore-40 to the Pico Back- BackPack hardware; it is the “3.5IN
Pack, the height of the plastic spacers DRIVER.BAS” file in the software
on standard pin headers will prevent downloads package.
the underside components from touchThe code is much the same as that
ing the PCB below. To do this, sand- found in the Display Drivers folder of
wich the headers between the Pico the Micromite firmware download.
BackPack and Explore-40 PCBs, then We have just changed the line in the
tack a few pins in place before solder- MM.STARTUP subroutine to suit our
ing the remainder and trimming the pin allocation. The “3” at the end indiexcess lengths away.
cates a landscape configuration, with
If you are doing something differ- the microSD card socket near the top
ent, we recommend test-fitting the of the screen.
parts first to be sure they will fit and
Load this file onto the Micromite (for
not cause any fouling with the LCD example, using the AUTOSAVE companel above. It’s also possible to fit mand), then perform a LIBRARY SAVE
the Explore-40 to the underside of the and restart the Micromite by pressPico BackPack PCB, although that will ing S1 or entering the CPU RESTART
make it difficult to access the buttons command. You should see the screen
or see the LEDs.
clear and you can run the GUI TEST
If you want to do that, we suggest LCDPANEL command to confirm it is
working.
To configure, calibrate and test the
touch panel, use these commands:
Fitting it to a Pico BackPack
The underside of the Explore-40
shown at actual size; note the
orientations of IC2 and D1. REG1
is also polarised, but its correct
orientation should be obvious.
panel. You can use IC2 to program
IC1, after all.
If you connect the Explore-40 to
a computer and open a serial terminal program such as TeraTerm, you
should be able to communicate with
the Micromite firmware. The default
baud rate is 38,400. You can press S1
and check that the Micromite’s boot
message is printed via the terminal.
The Explore-40 is now complete
enough to plan how you will fit it to
the Pico BackPack. The most significant difference is that the Explore-40
has components on its underside, so
it will not mount flush like a Pico
could.
The following assumes that you are
OPTION TOUCH 7,15
GUI CALIBRATE
GUI TEST TOUCH
We used low-profile header sockets to mount our prototype Explore-40, but if
you solder it directly to the BackPack PCB using standard header pins, you will
gain clearance since the Explore-40 will sit lower. With some care, the unused
SD card socket on the underside of the 3.5in LCD panels can be removed, giving
extra clearance below. Use solder-wicking braid to clean off any excess solder
left behind.
86
Silicon Chip
Australia's electronics magazine
If the required components and
jumpers are fitted to the Pico BackPack, the backlight is also driven from
IC1’s pin 26, just like the V3 BackPack.
This can be controlled using PWM
channel 2A. The following will set
siliconchip.com.au
the duty cycle and backlight brightness to 50%:
PWM 2,250,50
IR receiver & realtime clock
The IR receiver on the Pico BackPack is routed to the dedicated Micromite IR pin, pin 16, so the IR receiver
can be used by simply setting up the
IR interrupt with the IR command. The
command would be something like:
IR DevCode, KeyCode, IR_Int
A basic interrupt subroutine to test
this could be:
SUB IR_Int
PRINT “DEVICE:” DevCode
“KEY:” KeyCode
END SUB
The RTC commands support the
realtime clock chip:
RTC GETTIME
RTC SETTIME year, month, day,
hour, minute, second
You can then retrieve the current
time and date from the TIME$ and
DATE$ variables.
MicroSD card support
The Micromite lacks a native driver
for interacting with SD cards. Peter
Mather has again done some excellent
work in creating a CSUB driver to do
that. However, there are a few provisos to using this software. Since the
Micromite does not have an interface
for file handling (unlike the Micromite
Plus), everything is done via calls to
the CSUB.
The driver is quite simple and
cannot do things like create or
append to files. So, if you wish
to write to a file, the recommendation is to create a large file on
the card, which the driver can
then overwrite. Even with these
restrictions, the driver takes up
about one-sixth of the flash memory available for programs. More
background information on this
and suitable code can be found at
siliconchip.au/link/abxr
We have configured pin 4 as the
CS (chip select) pin for the microSD
card socket. This is the same pin
that is wired to the SD card socket
on the LCD panel for the Micromite
V3 BackPack. So you could try this
on a V3 BackPack, although we haven’t tested it.
siliconchip.com.au
Parts List – Micromite Explore-40
1 51 × 21mm double-sided PCB coded 07106241
1 16-pin USB-C data and power socket (CON1) [GCT USB4105]
1 5-way pin header, 2.54mm pitch (CON2; optional, for ICSP)
2 20-way pin headers, 2.54mm pitch
2 SMD 2-pin tactile switches (S1, S2)
Semiconductors
1 SS14 40V 1A schottky diode, DO-214AC/SMA (D1)
1 PIC32MX170F256B-50I/SO 32-bit microcontroller programmed with the
Micromite firmware, wide SOIC-28 (IC1)
1 PIC16F1455-I/SL 8-bit microcontroller programmed with the Microbridge
firmware, SOIC-14 (IC2)
1 MCP1700-3.3 3.3V low-dropout voltage regulator, SOT-23 (REG1)
1 red M3216/1206/SMA SMD LED (LED1)
1 green M3216/1206/SMA SMD LED (LED2)
Capacitors (all SMD M2012/0805, X7R)
1 22μF 10V X5R/X7R
2 1μF 16V
3 100nF 50V
Resistors (all SMD M2012/0805, ⅛W)
1 10kW (code 1002 or 103)
2 5.1kW (code 5101 or 512)
5 1kW (code 1001 or 102)
Optional extras
1 Pico BackPack (without Raspberry Pi Pico) plus 3.5in LCD (March 2022)
1 3.5mm jack socket breakout board (see panel and parts below)
Audio Breakout Board
1 double-sided PCB coded 07101222, 20 × 15mm
1 stereo 3.5mm PCB-mounting jack socket (CON3A) [Altronics P0094]
1 3-way pin header (CON3)
The Explore-40 module is a drop-in replacement for a Pico
on the Pico BackPack (described separately).
Kit (SC6991, $35): a
complete kit is available
for the Micromite Explore-40 with
all the parts listed (does not include the
Audio Breakout Board or Pico BackPack).
Australia's electronics magazine
October 2024 87
The driver file is named “SDCARD_
SPI1.BAS”. It is installed similarly
to the LCD panel driver, using the
AUTOSAVE and LIBRARY SAVE
commands.
We’ve also created a HEX file that
contains these two libraries loaded
into a working copy of Micromite
BASIC version 5.05.05, named “MM
BASIC SD ILI9488.HEX”. You can load
this with the onboard Microbridge or
a PICkit programmer.
Audio support
The audio driver is another CFUNCTION that is controlled via calls with
various parameters. This is based on
a similar driver we created for the
Advanced GPS Computer (June & July
2021; siliconchip.au/Series/366).
This uses a pulse-width modulation (PWM) output to synthesise an
analog voltage signal, with the PWM
switching frequency being filtered
out by a low-pass filter attached to
that pin. The analog voltage is varied
using a timer interrupt to update the
PWM duty cycle for each sample to
be played.
The big difference is that this driver
is capable of stereo output, although it
is limited to eight bits of resolution and
an 8kHz sampling rate. Given that the
Micromite has enough flash memory
to play only seven seconds of audio,
or enough RAM for about six seconds,
we think it is a fair compromise.
The AUDIO folder in the software
downloads contains several files,
including the CFUNCTION driver,
some encoded audio samples and
BASIC code to demonstrate how to
use the driver.
The samples are created as CFUNCTIONs, although they do not contain
executable code. They consist of a
32-bit header that indicates how many
bytes are in the sample, followed by
that many bytes. Stereo samples are
stored with the left channel data first.
A mono sample played in stereo mode
will play twice as fast since two bytes
are used every sample period.
The driver is installed by loading
the “CFUN_LIBS.BAS” file onto the
Micromite, then using the LIBRARY
SAVE command. Since the CFUNCTION returns a value, we need to do
something with that value, like print
it. Use this to start the driver:
PRINT AUDIO(0)
A sample is used by loading
its BASIC file, then performing a
LIBRARY SAVE. Tell the driver where
the sample is located like this:
PRINT AUDIO(1,
PEEK(CFUNADDR SAMPLE_NAME))
Then start playback with:
PRINT AUDIO(2) ‘mono
PRINT AUDIO(12) ‘stereo
The sound will play in the background and stop automatically. Using
values 6 (mono) or 13 (stereo) as
parameters will cause the playback to
loop endlessly. Playback can be forced
to stop with:
PRINT AUDIO(3)
You can also wait for playback to
finish with:
DO WHILE AUDIO(4)<>0:LOOP
The “BASIC_SUBS.BAS” file has
some more sample code and variables
that can be used to make it easier to
see what each parameter does.
The file named “AUDIO MMBASIC.
HEX” contains the libraries, samples
and BASIC code, alongside a working copy of Micromite BASIC version
5.05.05.
Notes
The 28-pin Micromite has somewhat limited peripherals, so there
are some limitations. For example,
the timer that provides the interrupt
to fetch new audio samples is the
same one used for the IR decoder. So
we don’t think it is possible to use
the IR and audio features at the same
time, although it should be possible
to switch between them.
The audio output uses two of the
remappable PWM channels, so the
PWM feature on pins 4 and 5 cannot
be used at the same time as the audio.
Pin 4 is mapped to the microSD card
socket, so we expect it will be used for
that feature instead.
In any case, the CFUNCTION libraries take up quite a bit of program memory, as do audio samples, if kept in
flash memory.
Remember also that the PIC32MX170F256B microcontroller can
be programmed in the C language
using the MPLAB X IDE. We did that
for the Digital Lighting Controller
(October-December 2020; siliconchip.
au/Series/351).
That older project can play stereo
audio from an SD card, so you might
find it helpful if you are thinking of
doing something similar using the C
language and the MPLAB X IDE.
Summary
The 3.5mm jack
socket breakout board
is a neat fit under the LCD panel,
even when mounted on header pins. Like
the Explore-40, you should trim any excess pin
length with flush nippers or sidecutters.
88
Silicon Chip
Australia's electronics magazine
If you are a Micromite fan and yearning for the features of the Pico BackPack, the Explore-40 is the perfect way
to bridge that gap. It adds microSD card
support and stereo audio features that
were missing from earlier Micromite
BackPacks.
There are some limitations to what
the Micromite can achieve, but it is
still a handy platform for learning the
BASIC language.
The Explore-40 also adds nice
touches, like the modern USB-C socket
and reset button. These features can
be handy regardless of whether the
Explore-40 is used by itself, on a breadboard or as part of a BackPack.
SC
siliconchip.com.au
SERVICEMAN’S LOG
I got the power
Dave Thompson
The other day, something relatively unusual happened around here, which
revealed a flaw in our system. For the first time in a very long time, we
experienced a power cut. It wasn’t just one of those ‘oh, the power has gone
off and has come back on in minutes’ cuts – it was off for many hours.
I assumed some contractor somewhere had dug a little
too deeply, or perhaps in the wrong place, and had put
the bucket through the cable to our part of town. I fully
expected things to come back online pretty quickly. After
15 minutes, I leaned across the fence to my neighbours and
asked if they’d also lost power, just in case it was something in our household that had given way.
Fortunately, they’d lost power too. Oh wait, that came
out wrong; I mean that it wasn’t a fault specific to me that
I would have to get someone to fix. Perhaps it was one of
those substation explosions you hear about. I could imagine the control room at the power station, with a map of
the city and bits of it going dark in sequence as the system
fails. Sadly, I think that’s just movie mayhem.
Either way, something had obviously happened to our
supply and we could do nothing but ride it out and wait.
This obviously left us dead in the water regarding our
computers, my workshop, our local area network internet connectivity – pretty well everything. Fortunately, we
have mobile phones, so we could at least maintain some
kind of connectivity.
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After 30 minutes, I bit the bullet and called our power
supplier. I soon discovered that I was gazillionth in the
queue for fault reporting and support, so I wasn’t going to
waste much time on that. It was obviously being reported
already; my whinging about it wouldn’t make much difference in the bigger picture.
I also didn’t want to burn up the remaining charge in my
phone battery, even though since the quakes here, I have
maintained several different USB battery packs so we can
charge phones. I was really caught short when the quakes
hit in 2011 and we lost power for a week. Back then, my
phone had only 24% charge to begin with. With no way
of charging it, it soon went flat.
The bad old days
Not that it was much good in the early days anyway,
because all the cell towers lost mains power and the backup
batteries only lasted two hours. Plus, they were so overloaded that the whole system crashed. If we were lucky,
the odd text might go through, but voice calls were mostly
impossible.
Australia's electronics magazine
October 2024 89
Items Covered This Month
• Unlit ruminations
• Workzone MIG (metal inert gas) welder repair
• Bando Technic 5D transceiver repair
Dave Thompson runs PC Anytime in Christchurch, NZ.
Website: www.pcanytime.co.nz
Email: dave<at>pcanytime.co.nz
Cartoonist – Louis Decrevel
Website: loueee.com
Of course, nothing worked once the towers’ backup batteries went flat. Landlines had been severed, and while
some users in some suburbs had communications, the rest
of us did not.
I vowed never to be caught out again. I have at least a
week’s worth of battery power here now for charging phones
or any other tech. As a bonus, and again, as a result of the
quakes, we have gas heating and cooking, so at least we
could make a cup of tea while we watch the house fall
apart in the aftershocks.
However, our newest gas fire, installed recently, requires
electric power to run. Given that this recent power cut
happened in the middle of winter, my concern was that
we’d soon get very cold. We also have several heat pumps
around the house to provide basic warmth in the winter
and cooling in the summer but, of course, they were offline
as well due to the outage.
Yes, I know this is a very first-world problem and that
many people, including those in so-called first-world countries, experience power loss regularly for various reasons.
However, it brought back a lot of bad memories for me, to
those times when we and others had no power for weeks on
end, in the darkest days of our post-quakes, semi-dystopian
society where, let’s not forget, almost 300 people died.
No traffic lights, no streetlights, no mobile phones, no
landlines. It was a strange time. The problem was that the
earth under everything in many parts of the city turned to
a liquid-like quicksand (a phenomenon known as liquefaction). All the pipes and conduits and anything else under the
tarmac on the roads just floated to the surface of the street.
The earthquake’s strength was such that it just lifted the
asphalt, circuit junctions and access covers and ruined the
roads. That’s aside from breaking all the pipes, cables and
whatever else was nestled inside those conduits.
This, of course, plunged entire suburbs into darkness.
Luckily – if there was a lucky side to it – it was February
and summer, so we didn’t really have to worry about heating. But, with all the sewers broken, there were no toilets,
no water, no power, no phone lines. We were cut off.
I realise that many other countries had things worse. At
around the same time, Haiti experienced a huge quake,
which killed thousands, as did Japan, with wider-reaching
consequences.
Not having power back then was a real problem. Everything in our home relied on power. My serviceman’s mind
sprung into action and, as soon as the shops were open, I
vowed to buy a generator. In the meantime, I had an old
gas cooker and an old gas heater that used the ubiquitous
9kg bottle of LPG.
One company was giving away gas (many companies did
this in an effort to help, whether it was free milk, bread
90
Silicon Chip
or gas), and I took my old bottle down to have it filled. Of
course, it was out of date, so they wouldn’t touch it, let
alone fill it. I bought two new ones from a nearby big box
store and had them filled for free.
I did have to queue for hours at each place, as milk, bread,
petrol and gas were being strictly rationed. It really was
an eye-opener as to how people behaved under duress. At
least our stove and (if we needed it) heating would work.
Anyway, back to our recent power outage. As I mentioned, power outages are rare here. The last one we had
was seven years ago, when we moved into this place. We’d
had the power off as we renovated the house, and when we
put it back on, it suddenly failed. Thinking it was something we’d done, I did as much troubleshooting as possible.
I could tell power was coming in from the wires, but it
died at the old ceramic pole fuse mounted on the house’s
bargeboards. I had to call the power company, and the guy
climbed the ladder and touched the wire and it simply fell
off. Easy job, I thought. But no, new pole fuses actually
have to go on poles. But the pole on our back section was
apparently an old pole (60 years) and not high enough.
So, the pole had to be replaced and the new fuse put on
top of it. Red tape holds the nation together, or so they say.
It was a completely ridiculous chain of events. Anyway,
that’s the last time the power went out, so it’s a rare occurrence, which is why I thought some contractor must have
dug up the cable or a substation had failed somewhere.
Time for the generator to shine
Whatever the cause, our house was dark and dead in the
water in the middle of winter. After three, I decided it was
time to dig out the generator I had queued to buy 13 years
ago, and fire it up. If the power was not going to be back
on for hours, we’d need to get something sorted.
I knew we had hours before the freezers started thawing,
but I wanted to hedge my bets. Even with the generator, we’d
have to be pretty careful what we plugged in; it isn’t one
of those huge Detroit diesel powered ones I worked
on at the airline back in the day.
Two of those could power a city!
Australia's electronics magazine
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This one might do some phone chargers, the fridge/
freezer and maybe the TV, at a stretch.
The first challenge was getting the thing out
of storage in my garage. You’d think a ‘prepper’
like me would have it set up and ready to go in a
purpose-built enclosure next to the house, but no.
And it is such an awkward thing to move.
It isn’t overly heavy, but it is a two-person lift because
there’s nowhere one person can pick it up and carry it from.
It has a frame around it, but no finger or hand holds. You
also cannot get a sack-barrow underneath it because it
seems like something would get bent or damaged if I
tried. So, it needs two people.
I could drag it from under all the rubbish I’d piled
on it to the garage door, but from there to the house
is quite a way, so I had to involve my wife. That,
of course, is a whole other column.
We managed to get it onto the porch, where
we could run it out of the weather and add a
cable through a cracked window to power what
we needed.
The next challenge was firing it up. In the interest of being prepared, I have started it periodically
over the years, ensuring I had enough petrol in it
and even a spare can next to it should the you-knowwhat hit the fan again. The problem is, of course, that petrol loses its punch over time and this lot had been in there
for a while now.
I didn’t want to just tip it out, but as the tank in the generator seems to have allowed what was in there to evaporate,
even with the fuel tap off and the cap tightly applied, I had
to refill it with the can I had. With the tank full, it should be
good for about seven hours if my calculations are correct.
Mind you, I failed maths so many times at school I can’t
even count!
All joking aside, I was hoping this thing would start. It
has a 7HP (5.2kW) motor and electronic ignition, according to the label, so I was expecting it to fire up easily. It
didn’t. In the usual design stupidity that many machines
seem to have these days, the pull cord has to be pulled at
a weird angle off-centre from the pull starter, adding drag
on the line and making it harder to start.
Whoever designed these things must have been part of
the company Bastards Inc. from that TV show, “The Fall
and Rise of Reginald Perrin”. Saltshakers with no holes
in them, gloves with just three fingers. Surely they’d look
at it and think, how can we make this work better? But it
appears not.
I pulled on the cord a dozen times but nothing happened.
With lots of blue language and gnashing of teeth, I realised
I hadn’t turned the fuel tap on. I know, I know. It’s the little
things that get to you. Anyway, once I opened that, with a
few pulls on the cord, it sputtered into life.
Boy, these things are loud! It was now sitting right outside the window, and I was rueing the fact I hadn’t built a
soundproofed box for it elsewhere and ran some cabling. We
might have power now, but the price to pay was the noise.
A comedy of errors
I still had to connect it up, which meant breaking out the
extension cords. Fortunately, I know how to roll these up
properly, given my years on the road in the music business.
Unfortunately, the last time I used the longest of my
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cables, which of course was the one I needed now, I was lazy
and just gathered it up and chucked it on the garage floor.
Now it was a rat’s nest, caught in everything possible on
the concrete. Great, there’s 30 minutes of my life I’ll never
get back. Note to self: roll the cables properly next time!
I plugged everything in and fired the generator again, this
time hitting the ‘power on’ button, a standard-looking panel
switch like you see on lots of equipment, similar to those
on the rear of a computer power supply. This should liven
up the two mains sockets provided. However, I got nothing. No power output. Hrmm, I must be doing something
wrong. It’s not unusual (Tom Jones Syndrome).
I haven’t used this generator other than to test it in the
past, and I might need to (shock, horror) read the instruction manual. Though quite where that manual is, I don’t
know. I could always hit the internet to find it. Oh, wait...
The control panel has two olde-worlde moving coil
meters that showed I should have 230V available from the
mains socket and 12V DC from the red and black banana
sockets beneath them. So the generator itself appeared to
be generating. I broke out my multimeter and tested both;
I got no reading from either socket.
Great; I’m glad this wasn’t a dire emergency because I
was really behind the eight ball here. There must be another
switch or something I was overlooking. I just couldn’t
see one on the fascia, so I had to go down on my hands
and knees, in the noise and smoke, to try to see what was
going on.
Finally, I found a circuit breaker, stuck around the back,
on the motor assembly. I threw caution to the wind and
pressed it, and was rewarded with beeps and lights through
the open window. The governor on the genny kicked in
too, so it sensed there was some load on it.
Why they didn’t put that breaker on the front panel is
Australia's electronics magazine
October 2024 91
another one of the design ‘features’ that people who never
have to use these things come up with. At least I know it
is there now.
So we sat down and thought: what was most important? My wife works remotely and so getting our computers and internet up and running was most pressing. The
fridge and freezer would stay cold for a while at least, so
we decided to prioritise getting our network up and the
internet back online.
That wasn’t much load for the generator; it was revving
like mad right outside our office window. On reflection,
that was not the wisest place to put it.
Just as I was reconfiguring the plugs to get everything
up and running, the office light came on. I’d switched it
on so I’d know when the power came back. Excellent! All
that mucking around for nothing. At least I’d wrung out
the generator and had shown up some flaws in my systems.
Next time, hopefully I won’t be caught as short!
92
Silicon Chip
Editor’s note: I wrote an article in the January 2020
issue titled “What to do before the lights go out” about
preparing for blackouts and emergencies. Since then, I
have purchased another inverter, a generator, extension
cords, power meters, jerry cans, propane cylinders and
numerous battery-powered lights and torches. While I
haven’t needed them much yet, as Dave implies, it pays
to be prepared.
Always put fuel stabiliser in the petrol you’re keeping
for emergencies. After a year, pour it into your car’s tank
and refill the can with fresh petrol (not E10; it’s hygroscopic and corrosive). If testing a generator, switch the fuel
supply off and let it die so you don’t have old fuel sitting
around in it for years.
Workzone Inverter MIG Welder repair
Several years ago, I purchased a Workzone gasless MIG
welder from ALDI Special Buys. I’ve done a lot of work
with this welder, which was reliable until recently.
I was building a bike rack for our bikes and all was going
well until I got to a particular section. The welder started running erratically, making it difficult to make a decent weld. It
was a hot day, so I thought it might be overheating. However,
the welder worked well again when I turned the job over.
I went on to the next section of the project. It was fine as
I was welding one end, but it would not weld at all when
I went to the other end. I went back to the initial end, and
it worked fine there, but once again, when I went to the
other end, it did not weld.
Then it stopped welding completely. I no longer thought
it was overheating as the overheat light was not on and the
welder felt cool. I hadn’t done much continuous welding
on this job; had I pushed the welder much harder on other
jobs, so it should have been all right.
Returning from lunch, I found that the welder still did
not work. It did nothing when I pressed the trigger, even
though the welder was obviously running, as I could hear
the fan and the power light was on.
I started troubleshooting it by dismantling the handpiece.
This is easy to do as there is a nut on each end. I got my
multimeter and tested the microswitch and found it was
working. So it was time to take the lid off and look further.
The front panel is held on with three screws, one on
top and two underneath. Another seven screws hold the
cover on. With the cover removed, I found where the thin
cable from the microswitch connects to the control board
behind the front panel.
I pulled the plug out, connected my multimeter to it
(on continuity mode) and pressed the trigger again. Nothing happened, indicating a break in the cable between the
handpiece and the welder. I then shorted the two pins on
the control board and the wire feed motor ran. I laid that
wire on the ground clamp, shorted the pins again, and the
welder sprang to life.
To replace the cable, I had to remove the clamp that
holds the outer welding cable to the welder and disconnect the ground cable from the circuit board. I removed the
screws from one end of the board and loosened the screws
at the other end so I could raise the board to access the nut
underneath it.
I found some heavier twin-flex, soldered it to the end
of the original cable and pulled it through the outer cable.
I reconnected both ends by splicing and soldering, then
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applied heat-shrink tubing insulation. I reassembled the
welder and got back to the job at hand.
B. P., Dundathu, Qld
Bando Technic 5D repair
I may also suffer from Dave Thompson’s “Serviceman’s
Curse”. Sometimes repair jobs take far more time than was
bargained for or is reasonable.
I recently bought a non-working HF amateur band transceiver, as it looked worthy of restoration. It’s a brand I had
never heard of, Bando from South Korea, dating to the late
1980s. I found the service manual, all in Korean, but fortunately, the schematics were all readable.
As with most transceivers of that era, valves produce
the output, in this case, two 6146Bs driven by a 12BY7.
The remainder is all solid state. As the final valves operate with an 800V plate supply, any service work must be
done carefully.
This high voltage is derived from an iron core transformer
via a bridge rectifier and filtered by two series 47µF/450V
capacitors with 470kW balancing resistors. On inspection,
one capacitor was a dead short, which put the entire 800V
on the other, which had obviously blown! I decided to
concentrate on the receiver side first. After removing the
capacitors, I temporarily disconnected and insulated the
high-voltage winding from the transformer to the rectifier.
Some cosmetic problems needed to be fixed first. A
power connector on the back panel was missing, and an
ugly heavy power cable passed through the rectangular
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hole with a home-made cable clamp. In addition, a large
toggle switch had been added, which I found was used to
turn off the filament supply to the 6146s. In addition, the
wires to the microphone gain control were damaged.
I removed the switch and associated wiring and drilled
out the hole to take a proper cable clamp with a new power
cable. I covered the rectangular hole with a small plate. The
top and bottom covers needed a good clean-up; a repaint
may be a good idea at some stage. A couple of knobs were
not original, but a friend reckons he could make some to
match using a 3D printer.
Now I could safely turn it on to check the receiver operation. The display came up, and the tuning knob changed
the frequency correctly on all bands. Connecting a signal
generator, some bands appeared to work, but several were
completely deaf. The band switch is of the wafer type;
using contact cleaner, I managed to get all bands working
except for the 28-30MHz ones.
A 1µV input signal gave an excellent SNR on all but the
top band in that range, which needed at least 20dB more.
I ordered some replacement high-voltage electrolytics, but
being impatient, I robbed three 350V capacitors from discarded computer power supplies and made up a capacitor
that could handle 1050V, together with 270kW balancing
resistors. That enabled me to get the transmitter working.
I connected a 50W 100W dummy load to the antenna
terminal and switched to Tune on the 7MHz band. Immediate success; I had a power output that I could peak with
the two variable capacitors of the pi-coupler. There is also
Australia's electronics magazine
October 2024 93
a Drive control that tunes the plate circuit of the 12BY7,
but it did absolutely nothing!
The circuit diagram shows a section of a three-gang variable capacitor. The other two sections are used for peaking
the receiver’s tuned circuits on either side of a low-noise
dual-gate Mosfet preamplifier (Q1). The drive control operates the variable capacitor via a couple of plastic gears.
On close inspection, the gears were moving, but the one
attached to the capacitor shaft via a friction fit was not rotating the shaft. For some reason, it was jammed completely.
It was purely fortuitous that it was stuck in a position that
had the receiver working reasonably well. But to achieve
maximum output power, it did have to operate.
I tried all sorts of ways to move it, such as sliding the
gear off and trying to rotate it with pliers, all to no avail.
How about removing the capacitor and sorting out its
problem? About three hours later, having used all my
solder-removing tools, including a hot air pencil, I had to
admit defeat. There are many connections to the capacitor on the circuit board, and even though it is single-sided,
it was tightly connected, mainly via the solid end plates.
Any further attempts could have damaged the PCB, so
I had to develop a Plan B. Looking at the circuit diagram,
there is a 10nF capacitor (C60) from the plate of the 12BY7
to the variable capacitor. How about disconnecting it and
adding an external capacitor? I had several suitable variable capacitors accumulated over the decades that I had
fortunately never thrown away.
Doing a quick lash-up of the connections, it looked workable, and sure enough, I could peak the drive voltage to the
6146 valves. I made a bracket from 1.6mm aluminium and
bolted it to the top of the original variable capacitor which,
by luck, had 2.5mm tapped holes on top.
Adding a knob was a workaround solution but not a satisfactory one. It meant that the top of the transceiver had
to be left off, exposing what turned out to be 170V peak-topeak at RF on the stator. That could cause a nasty RF burn!
But how could I connect to the original drive shaft? One
suggestion was to make up a 3D-printed gear to mesh with
the one already there, but it just would not fit. Another
alternative would be a couple of pulleys and a belt drive,
which also looked impractical. Then, I came up with the
idea of using two universal couplings. Looking at where
they would fit and the angle between the shafts, it seemed
a likely solution.
Off to AliExpress, and not surprisingly, there are heaps
of them from different suppliers for different shaft diameters. The ones in the transceiver are 6mm in diameter, so
I ordered a couple for a grand total of $14. They arrived
within two weeks, just after I also received a length of
6mm-diameter tubing.
As you can see from the photo, it all came together quite
easily. The only gotcha was having to carefully drill out one
end of the 6mm coupling to 6.35mm (1/4in), as that was
the shaft diameter of the 100pF variable capacitor. Tuning
with the front knob is now quite smooth and the drive can
be peaked accurately.
Remember the two extra gangs on the capacitor? The
receiver sensitivity and noise figure were quite good on
all but the top band, so I decided just to peak the slugs
on the coils slightly on either side of the middle of each
usable band. For example, on the 40m band, I peaked L9
at 7.1MHz and L16 at 7.2MHz. That applied
to all the other bands.
I now have a workable transceiver with a
clean 100W SSB output on all but the 10m
band. After many hours of work, I decided to
leave that for another day. Once the proper
high-voltage electrolytics arrive, I will
replace the temporary arrangement. Yes, it
took a long time, but the satisfaction of getting it to work more than made up for it.
SC
C. K., Mooroolbark, Vic.
Above: the Korean-made Bando transceiver
and a close-up of its RF section.
Left: the universal coupling (with the
connectors unplugged).
94
Silicon Chip
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10/24
Vintage Radio
The amazing NZ-made ZC1 MkII
military transceiver
In the early
phases of
WWII, the
New Zealand
Government
decided that
their troops
required a better
standard of field
communications
radio than what
they had. They wanted a transceiver that suited the conditions in New
Zealand (bushland) and the tropics (jungles).
By Dr Hugo Holden
T
he task was given to Collier and
Beale of Wellington, NZ. They
designed the first model, the ZC1 MkI
and, by April 1942, they had amassed
enough resources to build 750 units.
By December 1942, the first production batch was shipped.
There were a few minor variations of
the MkI model that are not discussed
here, as this article is primarily about
the MkII. The subsequent re-design
was handled by R. J. Orbell of Radio
Limited (Radio Corporation of NZ).
At least 5000 MkI units were manufactured, and around 10,000 units
of the MkII, although estimates vary.
I have seen one estimate that 30,000
total units may have been made, but
that figure could have been a target. The exact numbers may never
be known. The serial numbers were
somewhat non-specific and not helpful due to secrecy.
The ZC1 radio project was not a
cheap undertaking for the NZ Government. Accounting for a total number
of around 14,000 to 15,000 units, the
cost was $3,000,000 NZ Pounds in the
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Silicon Chip
1940s, equivalent to about $2,660,000
AU Pounds at the time. Translated on
the RBA’s pre-decimal inflation calculator, that is equivalent to AU$234
million today.
If the estimates of the ZC1 units
made are correct, the cost per set was
around $15,600 in today’s currency.
56 factories and 900 workers produced parts and sub-assemblies for the
radios. It took about 60 man-hours to
build one set; about 20 sets per week
could be made initially. Production
must have sped up as time passed
to at least 100 sets per week to complete around 15,000 units by the end
of WWII.
I have been unable to determine if
many sets were made after 1945. It is
possible that some new ZC1s were
manufactured to support the NZ and
British occupation forces in Japan
(J-Force) during 1945-1948.
The ZC1s saw service in the Pacific
war campaign, and many were sold to
the Middle East; however, it was too
late for them to see any significant use.
After the war, ZC1s were deployed
Australia's electronics magazine
by NZ Government agencies for various mobile and fixed applications
until the 1960s. They then started
turning up in Army Surplus stores in
good numbers, many being cannibalised for components. They were typically used by radio hams on the 40m
and 80m bands (7.5MHz and 3.75MHz,
respectively).
A ZC1 radio was installed in the
Radio Room of the Grammar School
that I attended in Auckland in the
1970s; I cannot recall if it was the MkI
or MkII model. By then, I had already
seen ZC1 radios and many components that had been removed from
them in Army Surplus stores.
In the early 1970s, my brother used
an open-frame relay taken from a ZC1,
in conjunction with a capacitor, to
build a mains light bulb flasher.
Marine conversions
ZC1 radios also found their way
into fishing boats and other marine
applications. Many were modified
to be marine band radios; one of my
MkII radios had its transmit VFO
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Photo 1: this crystal module allowed
a ZC1 radio to be easily converted to
operate on marine frequencies.
Photo 2: the red and blue screws
on the tuning dial, plus the two
small windows at the top, allow the
operator to set it up to flick between
two specific frequencies instantly. The
radio’s front panel has a space for a
pocket watch.
replaced by a Pierce crystal oscillator
circuit running at 2128kHz, a marine
frequency. I converted it back to the
original spec.
Collier and Beale supplied a conversion kit for marine use in the post-war
era. Photo 1 shows the modification I
found in one radio; it may well be by
Collier & Beale.
Many ZC1 radios acquired all kinds
of modifications; unmodified ones
became very hard to find. These days,
due to the historical significance of
these radios, most owners want them
restored to their original condition.
Unusual features
As seen in the photos, one of the
attractive features of the radio’s front
panel is a pocket watch holder. Finding a period-correct military-grade
pocket watch to fit in that holder is a
challenge, but I did.
Also note the red and blue rods on
the main receive and transmit tuning knobs, called “Flick Set Screws”,
shown in Photo 2. These allow
mechanical storage, if you like, of two
frequencies; the tuning knob returns
(flicks) to the position and frequency
where the screws were tightened when
the Flick knob is deployed.
One thing that characterised both
models of the ZC1 was the ability to
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transmit and receive on two different
frequencies.
Design and specifications
The radio is a very solid affair, built
into a steel enclosure, the inside of
which is heavily copper plated. The
front cover (Photo 3) fits tightly with
a rubber seal. No harm would occur if
the unit were dropped in water with
the front cover on.
The main assembly is ejected from
the housing by two large front panel
screws and slides out for easy servicing.
The vibrator transformer (at lower
right on a sub-chassis, see Photo 6) is
encased in a shielded container; all
measures were taken to prevent RFI
from leaking out of the vibrator power
unit and creating radio interference.
There is minimal background interference with the original V6295 mechanical synchronous vibrator.
When using an electronic vibrator replacement (as I described in the
June-August 2023 issues; siliconchip.
au/Series/400), no interference of any
significance occurs. Those articles
described several different suitable
designs. Besides no contact wear, some
of those designs have the additional
advantages of higher efficiency and a
higher HT output.
The ZC1 was specifically designed
for easy servicing (unlike much modern equipment). It was very well documented, not just with a comprehensive
working instruction manual for the
operator but also circuit diagrams and
Photo 3: the front cover is a tight fit to protect the radio from mud, water etc
during transportation.
Australia's electronics magazine
October 2024 97
Photos 4 & 5: a photo of a suggested ground station setup from the radio’s manual, and how the radio could be mounted in
a truck.
a parts list with extraordinary detail.
The two manuals were labelled with
“New Zealand Wireless Sets & Stations
No. ZC.1, MK.II.”.
Photo 4, taken from the working
instructions manual, shows a typical
setup of a ZC1 MkII radio in the field
with a vertical whip antenna. Photo
5 depicts a mobile application in the
back of a truck.
As well as parts lists, the manufacturers supplied the Army’s Signal
Engineers with comprehensive details
about the radio that were never generally supplied for domestic radios.
For example, they include detailed
descriptions of each of the coils and
transformers, including things like
the exact number of turns used, the
size of the former, the type of wire,
the SWG wire size, the inductance
value with the % tolerance, whether
the coil was wound bifilar and the
coil base diagrams. The DC resistances of the inductors were also
documented.
This is by far the most detailed information available for any radio I own.
If any of these parts fail in the future,
it would be an easy task to replicate
them. The voltage on every valve electrode is also well documented in the
manuals.
Power supply
The radio is powered by a 12V storage battery, typically two 6V units
in series for the ground stations, or
the 12V battery in a jeep or truck for
Differences between the ZC1 MkI and MkII
The MkI model was a single-band 2-6.5MHz transmitter and receiver (transceiver). The MkII version was split into two
bands: 2-4MHz and 4-8MHz. Other differences include that the MkI model did not have an MCW (Morse code) transmit
mode.
The other major difference between
the MkI and MkII units is that the MkI
used a non-synchronous vibrator supply and two 6X5 valves as HT rectifiers, as shown in Fig.a. Also, in the
MkI unit, there was a switch to select
between a higher or lower HT voltage.
In the MkII, however, the switch
was dispensed with, and a synchroFigs.a & b: the ZC1
nous vibrator, the model V6295, was
MkI power supply
deployed. The 6X5 valves were dis(above) differs
pensed with too – see Fig.b.
significantly from the
The negative output of the MkII
MkII (left) as it uses
a non-synchronous
supply is connected via resistors to
vibrator and HT
ground and a voltage of around -50V
rectifier valves
to -60V is developed across them.
(6X5). The ZC1 MkII
This is used to cut off the valves in the
power supply used a
transmitter section when the radio is
synchronous vibrator,
in Receive mode. In Transmit mode,
dispensing with the
the resistors are shorted out, boosting
two 6X5s.
the HT voltage by an additional 50V.
98
Silicon Chip
Australia's electronics magazine
siliconchip.com.au
Photo 6: a
top view
of the ZC1
MkII chassis.
Note the large
brown tapped
antenna
tuning
coil at top
middle.
mobile use. Although the unit was said
to be “portable”, it weighed 27kg, and
somebody had to carry the batteries
too. For this reason, many units were
fitted into jeeps and trucks.
Two people could carry the ZC1
easily as it had handles on each side
of the cabinet. For one person to carry
the unit long distances by themselves,
they would have to be fit and quite
strong.
The MkII radio’s current consumption is quoted at 2.8A in Receive mode
with Sender off and 3.8A with Sender
on. In send RT mode, it is 4.9A; close
to 2A of that is for the valve’s heaters. The 6.3V heater valves are strung
in series pairs across the 12V power
supply; since there are 11 valves in
the radio, one valve requires a series
heater ballast resistor.
With an 80Ah battery, the usable
life is in the vicinity of 20 hours,
with the transmitter used 25% of the
total time.
Transmission power & modes
The ZC1 MkII RF output power
is in the order of 2W. A near-perfect
impedance match into a 50W load can
be made with an impedance-matching
transformer and slightly modified coupling, giving 3W output on 80m and
easily 2W on 40m.
The transmission modes are CW
(carrier wave), RT (carrier wave amplitude modulated by the microphone)
and MCW (Morse code telegraphy,
where an audio tone modulates the
carrier wave).
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The 800Hz tone oscillator was
enabled in both CW and MCW mode
(even though the modulator is not
used in CW mode). The oscillator output was cleverly coupled to the audio
stage and headphones so the operator
could hear a ‘sidetone’ or beep when
the Morse key was pressed.
In RT mode, the sidetone was
instead the sound picked up by the
microphone, helping the operator to
‘hear himself talking’ in the headphones (similar to analog telephones).
Antenna
The ZC1 was generally used with a
vertical 34-foot (10.4m) rod antenna,
supplied in several sections. The
transmission range was 25-35 miles
(40-55km) in CW mode and around
10-20 miles (15-30km) in vehicles
with 8-to-12-foot (2.5-3.5m) whip
antennas.
Wire antennas were also an option,
such as an inverted-L or T-shaped
wire. The ZC1 has a large two-inch
(51mm) diameter antenna tuning coil
with many taps, allowing a significant range of antennas to be used.
This large coil with the brown former
can be seen in Photo 6, sitting above
the chassis and behind the front panel
and switches that select the coil taps.
Component selection
The components in the ZC1, like
knobs, potentiometers, switches, dials,
valves, sockets, coils, shielding cans,
variable capacitors, resistors and fixed
capacitors were all of outstanding
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quality. These radios made for an
extremely attractive and economical source of parts for many projects.
These were especially good for young
people interested in learning radio and
electronics but short on cash.
The solid black phenolic knobs and
other parts, even today (80 years later),
look good as new.
There was a shortage of components
in the early 1940s, especially capacitors. Many of the capacitors, including the mica types used in this radio,
were made in New Zealand. The mica
came from local mines. Many of the
wax-paper capacitors were also made
in NZ, although some were imported
(see notes on the “Dwarf Tiger” capacitor found inside the metal housing of
one capacitor below).
The electronic components in the
ZC1 were heavily ‘tropicalised’ with
wax impregnation. Even the usual
wax-paper capacitors in the unit were
double-sealed inside additional metal
housings with a waxy oil to prevent
moisture ingress. All the other transformers were impregnated and sealed
in metal containers as well.
Even the hook-up wire was said
to have been treated with a “non-
vegetable lacquer”. This was all in aid
of reliability in moist bush or jungle
environments.
Transmitter circuitry
The circuit diagram is shown in
Fig.1. The modulation source for the
MCW mode is acquired by creating
a positive feedback pathway so the
October 2024 99
Fig.1: the ZC1 MkII transceiver circuit. The signal inputs (mic, line & key) are towards lower right, while the earphone outputs are just above those. The top half of
the circuit forms the transmitter, while the lower half is the receiver. They share the antenna at lower left.
100
Silicon Chip
Australia's electronics magazine
microphone amplifier stage based
around valve V1G (6U7G) oscillates.
This is easily achieved because the
microphone, being a dynamic type,
requires a microphone-matching
transformer to drive the grid of valve
V1G. A feedback capacitor is switched
in to make the preamp stage oscillate
at 800Hz.
The 6U7G valve was used extensively in both the transmitter and
receiver sections. It made sense to use
the same valve type for as many applications as possible in the one radio to
save on carrying different spare parts.
Valve V1G drives the 6V6GT Class-A
modulator valve, V4B.
The transmit VFO (V1F) is another
6U7G, followed by a 6U7G buffer stage,
V1E, and a 6V6GT RF output stage,
V4A. Generally, a 6V6 can generate
around 2-4W of RF (or audio) output
power in a single-ended application.
These valves were also popular in
domestic radio audio output stages
and as guitar amplifiers.
6U7s are a very capable RF pentode, described by RCA as a “Triple
Grid Super Control Amplifier”. This
means they are suited to applications
involving AGC circuits and gain control. They were also a common valve
type in the 1940s era. It was said that
the 6U7 was the most common valve
to find in junk sales in NZ. The 6U7
is very similar to the 6K7 found in
domestic radios of the time.
The 6U7 was abundant in Australasia and had many manufacturers
besides the usual RCA, Kenrad and
National Union brands. Australian
Philips made them, too, for the Department of Defence, and supplied them
in very attractive boxes with Art Deco
artwork (see Photos 7 & 8). The logo
engraved on the 6U7G valve base in
my set indicates it was made for the
Australian Department of Defence.
Receiver section
The receiver in the ZC1 is a single
conversion AM superhet radio with a
BFO (beat frequency oscillator) added,
based on a 6U7G pentode, V1D. The
valve lineup is a 6U7G RF stage (V1A),
a 6K8G triode-hexode converter (V2A),
a 6U7G 465kHz IF stage (V1B); a 6Q7
detector, and first audio preamp stage
V3A.
The receiver’s sensitivity was quoted
as 1.5μV at 8MHz, varying above and
below that over the bands a little, being
3μV at 2MHz. However, the output
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Photo 7: the Philips valves for this set
came in decorative cardboard boxes.
Photo 8: the original 6U7 variable-mu
pentode.
level was not stated; it probably was
around 50mW into the headphones or
a 100W dummy load.
The audio output stage is only
designed to drive headphones, so
the designers deployed yet another
6U7G RF pentode, V1C, in a triode-
connected configuration to act as the
audio output valve.
The audio output power of a ZC1
is a mere 50mW with low distortion,
although it will deliver 150mW with
significant distortion, pushing the
6U7G RF valve to its limits in this
application. This result is satisfactory
for the 100W headphones used and for
speech but is not good enough to drive
an extension speaker or music.
Some historical articles mentioned
distortion in the audio. The main cause
for it, aside from the non-linearity of
the grid voltage versus anode current
transfer function, is that even by 100150mW, the 6U7G’s G1 grid is drawing
current due to the high drive level
exceeding its bias voltage.
Restoration
I had replaced the electrolytic
capacitors in my ZC1 radios over
30 years ago. The other capacitors,
which included wax-paper types and
moulded mica types, were still in good
condition when the radio was 50 years
old, but that was 30 years ago. Now
those capacitors are about 80 years old.
On re-testing them, I found that
all the capacitors had deteriorated,
including the mica types; nearly all
had developed measurable leakage.
While the wax-paper types fared better than most due to being immersed
in oil inside steel canisters, over time,
the rubber seals failed where the canister and the phenolic end disc mated
together, and the lower molecular
weight part of the oil or wax started
to leak out.
Many of the mica caps in the ZC1
were custom-made by Radio Corporation, while others were American
types made by El-Menco. These were
also amazingly good for their age. The
ZC1 MkII also used three 1in (25.4mm)
diameter twist-lock electrolytic capacitors.
In vintage radio restorations, people often replace the original chassis-
mounted capacitors with radial or
axial types under the chassis. I don’t
subscribe to that, as it looks non-
original and messy.
New twist-lock capacitors are sometimes available in that size. Of late,
though, they have been more difficult to acquire, so now I re-build them
instead. I start by machining out the
base of the capacitor using a lathe. If I
find any latex rubber, I discard it and
clean the inside of the canister, as latex
can contain halides, which attack aluminium.
I machine a 10mm-thick plug from
phenolic material to fit the hole I created in the capacitor’s base. I then cut
two M2 threads in it for screws and
lugs. I also drilled 1mm holes beside
those screw holes to pass the wires
through from the replacement electrolytic capacitors – see Photos 9 & 10.
I glue the plug in place with 24-hour
epoxy resin. Don’t forget to label the
polarity of the pins before gluing! To
do that, I drill a small countersink and
fill it with a dot of red paint. When a
multi-section part is required, I stack
the capacitors on top of each other in
the canister and add more terminals.
Replacing the wax-paper
capacitors
There are many wax-paper and mica
capacitors in the ZC1. I replaced the
mica capacitors with new resin-dipped
18.7mm diameter hole
10mm thick Phenolic
plate (18.6mm diam.)
Panasonic 47μF 450V (18.1mm diam.)
Photos 9 & 10: after replacing the electrolytic capacitor within the can, I glued
the end back on. The new eyelet tags are soldered to the capacitor leads.
siliconchip.com.au
Australia's electronics magazine
Photo 11: soldering the end onto one
of the wax-paper capacitor cans.
October 2024 101
◀ Photos 12 & 13: end
caps for the waxpaper capacitors
made from PCB
material and the
finished capacitors.
Fig.2: an easy way
to add an extension
speaker to the ZC1
MkII.
500V silver mica types and the wax-
paper types with polypropylene film
capacitors, fitted inside the original
metal canisters.
When replacing the wax-paper
capacitors, I found the best method
was to first desolder the internal
capacitor wire from the eyelet/tag at
the end with the phenolic insulator.
Then, holding the capacitor (with
protective tape around its body) in
the lathe chuck, I carefully go around
the circumference near the far end
with a junior saw to create an initial groove.
After that, I cut the end off with the
saw and slide the capacitor contents
out of the canister. Next, I drill out the
rivet and tag in the phenolic insulator
and discard them. These tags were in
poor condition; the brass was quite
brittle where it was sharply folded,
and prone to cracking.
After that, I smooth the end with a
file while rotating in the chuck, then
smooth it further with 400-grade sandpaper. Once ready, I fit 1/8in (3.175mm)
diameter silver-plated brass eyelets to
the phenolic end.
I use fibreglass PCB material to
replace the end that was cut off. It is
easily cut into discs using a 22mm
diameter hole saw in a drill press.
I then make a 1/8in central hole and
attach a screw and nut to secure it.
I then used the lathe to machine the
perimeter down to 16.8mm, to be a
close fit inside the end of the metal
canister. I fit the same eyelet type to
this end cap, visible in Photo 12.
The replacement capacitor is prepared with a phenolic spacer and
some Scotch 27 fibreglass tape, so it is
a firm fit in the original canister. I then
recess the discs about 0.5-0.8mm into
the end of the metal canister before
soldering it. This way, a small well
for the solder is created between the
canister’s edge and the eyelet projecting from the copper side of the PCB
material.
Polyimide tape must be wrapped
around the capacitor body, right up
to the edge being soldered, or the solder will track down the outside of the
canister, spoiling the appearance of
the capacitor body. I use a soldering
iron set at 400°C to heat the edge of the
canister all the way around initially to
create a strong bond, then fill the well
with more solder.
The same principles apply to
re-building the 200nF capacitors,
except I initially used a 25mm hole
saw to make a larger disc.
I decided that having flying leads
on the capacitors was a better way to
mount them than the tags they once
had.
An interesting finding while restoring these capacitors: the 20nF types
were custom-made by Radio Corporation with a brown paper valve over
them inside the canister, also filled
with wax.
They must have been running low
on their own production because
one of these four capacitors had an
American-
made 20nF 600V “Dwarf
Tiger” capacitor hiding inside.
Replacing the mica capacitors
Most of the mica capacitors that had
become leaky were American-made
El-Menco parts. One was made by
Radio Corporation in NZ.
Photo 14 shows the underside of the
Photo 15: the
custom 12V
DC power
connector
used by the
ZC1 radios is
now hard to
obtain.
Photo 14: the underside of the chassis is pretty neat; it was made to be easily
serviced. Most resistors have already been replaced, as the old ones were way
out of spec.
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Silicon Chip
Australia's electronics magazine
Photo 16:
my newly
manufactured
replacement
12V DC
power cord
for the radio.
siliconchip.com.au
ZC1 after re-capping it. In the past, I
had replaced nearly every carbon resistor, except just a few, as they measured
way out of spec.
As well as many resistors having
gone high in value, one 50kW power
resistor was open-circuit. I carefully
removed the paint to inspect it to find
out why it happened. It turned out
that there was a discontinuity in the
carbon film.
Optimising transmission on the 40m and 80m bands
The RF output impedance of the ZC1 best suits long wire antennas. I found that by using
an impedance-matching transformer (an ‘unun’) with modified coupling to the output
coil, the output could be optimised for a 50W load. This also makes measuring the output power with standard equipment very easy. It requires the addition of two capacitors
inside the unit and the unun outside.
The capacitors are selected with positions 10 & 9 on the switch, as shown in Fig.c.
The unun matches the resulting ~12.5W output impedance to 50W (Fig.d). The Amidon
core and wire (see photo at the bottom of the panel) come as a kit (AB200-10). With
this arrangement, 2W is easily delivered to a 50W load on 40m and around 3W on 80m.
The 12V power cord
One of the tricky parts to get for the
ZC1 these days is its polarised 12V DC
power cord and plug. The original type
was a substantial black phenolic connector with two large-diameter rubber-
covered wires – see Photo 15.
I used my lathe to hand-make a compatible 12V plug from some phenolic
plate, machined brass inserts, electrical insulating valves and brass rod
– see Photo 16. A friend in the USA
also made a CAD file to 3D print this
connector.
Making an extension speaker
As noted, the ZC1 uses a 6U7G radio
frequency valve (triode connected) as
the audio output amplifier. The designers pushed this valve to near its maximum ratings: a plate dissipation of
up to 2.25W and a screen dissipation
of 0.25W.
The 2kW cathode resistor for the 6U7
can be reduced to 1.8kW to gain a little
more power, which is in the range for
the specification of the original carbon resistor. If the valve is exchanged
for a 6K7G, which has higher plate
dissipation but is otherwise similar
to a 6U7, the cathode resistor can be
lowered to 1.2kW, which gives a good
improvement.
I wanted to keep the set original
but add an extension speaker. It is
best to match the speaker with a small
autotransformer, the design of which
is shown in Fig.2. The taps can be
selected to suit any speaker impedance (the impedance ratio is the square
of the turns ratio). At this low power
level, the laminated iron core transformer I used has a flat, undistorted
response from 50Hz to 20kHz.
I mounted the matching transformer
inside a speaker box with a spare 32W
speaker – see Photo 18 (shown overleaf).
Other options to increase the audio
output power include moving to a
higher power rated valve such as a 6V6
siliconchip.com.au
Fig.c: this simple modification to the coil switching arrangement can be used with an
external impedance-matching transformer to obtain good performance into a 50Ω load.
Fig.d: this ‘unun’ matches the 12.5Ω output
impedance of the modified radio to a
standard 50W antenna.
Right: the autotransformer that adapts the modified set’s 12.5Ω antenna impedance to 50Ω
is housed in a small diecast box.
Silicon Chip kcaBBack Issues
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Australia's electronics magazine
October 2024 103
or 6K6. However, that requires modifying the radio’s circuitry, and the small
output transformer’s primary current
can only be pushed so far.
According to the data sheets, transformer T1A’s primary has 3000 turns
of 43 SWG wire, which has a current
rating of only 18mA. Another option
is an active external speaker.
Adding a frequency counter
Photo 17: the frequency counter connects via the lamp socket on the front,
modified to pass enough of an RF signal for this to work.
Accessories
My ZC1 headset
and microphone.
The headphones’
cord is a little
frayed but both
still work fine.
The ZC1 came with several accessories, many of which supported its
use as a ground station – see Fig.e.
The minimum requirements, aside
from the batteries and the antenna,
were the headphones, microphone
and Morse key.
The headphones and microphone (see Fig.f and photos) are
both dynamic types. They use the
same dynamic inserts with a DC
resistance of around 40-45W. The
ones in the headphones are wired
in series and have a total resistance
of around 95W and an impedance
close to 100W at 1kHz.
Other items included a remote
control box for the radio (Fig.g), the
whip antenna kit, the battery pack
and a spare valve kit containing every
valve plus a spare V6295 vibrator.
There were also two 6V lead-acid
80Ah batteries in wooden boxes.
The remote control allows the ZC1
to be operated 100m away via a connecting cable. Two remote control
units could be used, and the operators could talk to each other like a
telephone link. The remote control
units came with a satchel to carry
the microphone and headphones.
An add-on power amplifier, type
ZA-1, was an option. It incorporated
type 807 power valves to boost
the RF power. Not nearly as many
booster amplifier units were made
as the ZC1 radios.
104
Silicon Chip
There is a connector on the front
panel of the ZC1 to power a reading
light. One of its connections is via a
resistor.
Adding some coaxial cable and
small coupling capacitors into the
radio allows the signal from the Transmit and Receive VFOs to be exported
via that connector – see Fig.3 & Photo
17. This modification does not alter
the original function of the front panel
lamp socket.
The dynamic
microphone
insert (at upper
left) is easily
removed from the
handpiece. Two of
the same inserts
are used in the
headphones.
Australia's electronics magazine
siliconchip.com.au
Fig.3: adding a couple of small capacitors and some coax allows the front
panel light socket to be used for monitoring the LO or transmitter frequency
with an external frequency counter.
Due to the low values required for
the coupling capacitors (1.1-2.2pF),
the set barely requires retuning after
adding them. The C7G and C7H trimmers can be adjusted on the transmit
side and C7C and C7B on the receive
side (L/O) to fractionally reduce their
capacity if required, but I found it
unnecessary.
The capacitance of the coax forms an
Fig.e (above): some of the available
ZC1 accessories.
Fig.f (right): the microphones,
headphones and Morse code
key available with the set. The
microphones and headphones used
the same type of dynamic insert.
AC voltage divider and transforms the
impedance. The presence or absence of
the external frequency counter results
in a negligible effect on receive or
transmit frequencies.
Since one of the connections on
the lamp circuit is to positive and not
ground, it is a good idea to put two
DC isolating capacitors in the banana
plugs in case the chassis of the frequency counter and the ZC1 chassis
come in contact.
In receive mode, the peak voltage
is only 30mV; not all counters could
work with that low a level and might
need a buffer amplifier. My counter
has an internal buffer/amp. In transmit mode, the output level is higher
at just over 200mV peak.
The frequency counter can be modified to switch out its 465kHz offset in
transmit mode to automatically show
the correct receive and transmit frequencies without manually switching
the offset on the counter.
Conclusion
Fig.g (left): up to two remote
control units could be used with a
ZC1 radio. They could be located
100m or more away from the
radio, connected by wires.
siliconchip.com.au
Photo 18: the completed extension
speaker. The impedance-matching
transformer is also inside the box.
Australia's electronics magazine
The ZC1 MkII radio is a masterpiece
of high-quality radio engineering and
a very impressive feat for New Zealand’s wartime radio engineers. It is
so well built that many are still functional 80 years on.
As expected, the capacitors and
resistors deteriorated over that time
frame. In my ZC1 radios, all the coils,
transformers and original valves
remain in good order.
The radio is an excellent, sensitive receiver for shortwave listening. It remains one of my favourite
radios. Unfortunately, many that were
deployed for Marine use rusted significantly, but with enough work, that can
also be remedied.
SC
October 2024 105
Mouser Electronics’
new Melbourne office
by Tim Blythman
Mouser recently opened a new Australian Customer Service Centre.
The launch event was held at Hotel Chadstone while the office is
located in the Melbourne suburb of Notting Hill. We attended the launch
event to see what this means for their customers (including us!).
Y
ou might have seen Mouser’s
announcement about their new
Melbourne Customer Service
Centre in the Product Showcase section of the March issue (siliconchip.
au/Article/16169). It is the first Mouser
Electronics location in Australia or
New Zealand. Before that, the nearest
location was in Singapore! To celebrate
this occasion, an event was held in the
Altus East Room at the nearby hotel.
Mouser representatives present
included staff from the Melbourne
Customer Service Centre, as well as
other staff responsible for the Asia-Pacific region. Mark Burr-Lonnon,
Mouser’s Senior Vice President of
Global Service and EMEA (Europe,
Middle East and Africa) and APAC
(Asia-Pacific) Business was there.
Other attendees included representatives from local electronics and
engineering firms. We caught up with
the folks from Microchip Technology,
who are always enthusiastic about
their new and upcoming products.
One sentiment that was discussed
at the event is that we should expect
more innovation over the next few
years. Engineers now need to spend
less time chasing parts and alternatives, as was common over the last few
years. That’s certainly a relief!
This artist’s impression, based on an aerial photo, shows the past and future expansions of Mouser Electronics’
headquarters and distribution centre in Mansfield, Texas. The new distribution centre nearly doubles the warehouse size;
the three-storey building uses the latest robot pickers to pick orders (1000ft2 is 92.9m2).
106
Silicon Chip
Australia's electronics magazine
siliconchip.com.au
A rendering
of the robotic
storage/
picking
system inside
Mouser’s
expanded
Global
Distribution
Center.
Source: https://
youtu.be/
FDCS9qSLVpY
We have also noticed a lot more
products in stock these days; it’s
almost back to the pre-COVID situation.
We met several of the Mouser customer service staff who work at the
Melbourne Customer Service Centre.
Their general message is that they are
now able to provide a local presence
in the same time zone, language and
currency.
Previously, the alternative would
have been to contact someone in Asia,
a few hours behind our time zone.
There was no mention that any local
stock would be held, but Mouser’s
shipping options are generally quite
fast, even with most products coming
from the USA.
Mouser Electronics was founded
(as Western Components) 60 years
ago, in 1964, by Jerry Mouser. He sold
electronic equipment and parts to students in California before moving the
company to Mansfield, Texas in 1986.
Mark was keen to point out that
Mouser is still supplying parts at
small-to-medium volume for design,
research and development. Mouser
continues to focus on engaging with
students, makers and engineers.
Much of the presentation included
the typical slideshows and spreadsheets, but there were some interesting insights. Nearly half of Mouser’s
sales in Australia and New Zealand
for the last few years has consisted of
semiconductors, including devices
like embedded hardware and sensors.
Facility expansions
Mouser Electronics has greatly
grown their inventory in the last few
The presentation
The main presentation at the event
was from Senior Vice President Mark
Burr-Lonnon. He is originally from
the UK, but has spent over 20 years
in Texas in the USA, where Mouser
Electronics is based. His accent is
remarkably like that of an Australian.
Mark provided some background on
Mouser and its sister and parent companies. Mouser Electronics is a subsidiary
of the Berkshire Hathaway group, and
Mark joked that he is only a few rungs
down the ladder from Warren Buffett!
Mouser’s sister company, Braemac,
is an Australian-based components
distributor. It also has offices in the
same location in Notting Hill.
siliconchip.com.au
A slide showing the hierarchy of staff in Mouser’s new Melbourne office.
Australia's electronics magazine
October 2024 107
Ideal Bridge Rectifiers
Choose from six Ideal Diode Bridge
Rectifier kits to build: siliconchip.
com.au/Shop/?article=16043
28mm spade (SC6850, $30)
Compatible with KBPC3504
10A continuous (20A peak),
72V
Connectors: 6.3mm spade
lugs, 18mm tall
IC1 package: MSOP-12
(SMD)
Mosfets: TK6R9P08QM,RQ (DPAK)
21mm square pin (SC6851, $30)
Mouser’s part inventory peaked in late 2023 at over two billion items (blue
bars). The red bars indicate products they had on order at the time.
years; that is good evidence that the
parts shortages of recent times have
mostly subsided. Mark noted that they
will continue to increase their inventory, anticipating that the demand for
electronic components will continue
to increase in the near future.
Another slide highlighted just how
many unique products Mouser has in
stock from many well-known suppliers. We counted over thirty suppliers in this list, including names like
Microchip Technology, Texas Instruments, Analog Devices, Vishay and
Renesas Electronics. Mouser states
that they currently have nearly 1.1
million different parts in stock.
Mark also discussed Mouser’s ongoing expansion of its headquarters
and distribution centre with modern
automation technology, including the
AutoStore robotic picking system.
The distribution centre has nearly
doubled in size. It can be seen at
in the video at https://youtu.be/
FDCS9qSLVpY
The Mouser AutoStore installation has 225,000 bin locations served
by 119 robots, and the robots can do
both restocking and picking. You can
see a YouTube video of the AutoStore
robots and system at https://youtu.be/
mQU2BVrnuH4
Another point that was mentioned
was their measures against counterfeit
components. Mouser wants to ensure
that they only sell authentic parts.
108
Silicon Chip
Our interview with Mark BurrLonnon in the October 2022 issue
(https://siliconchip.au/Article/15514)
also covered the accreditation and certifications that Mouser has earned to
fulfil those requirements.
Networking
One of the reasons we had heard
for choosing Melbourne for Mouser’s
Australian office was the thriving tech
community and manufacturing base,
including manufacturers and related
services.
After the main presentation, there
was another opportunity to network
with other attendees. We spoke to
representatives of a few different
companies. It was interesting to hear
of the diverse engineering and manufacturing companies operating in
Melbourne that use Mouser products.
Conclusion
We are finally seeing a return of
in-person events in place of the virtual events that have been occurring
over the last few years. We were glad
to meet the Australian Mouser team in
Melbourne, as well as catch up with
some other familiar faces.
It’s promising for the electronics
industry that Mouser Electronics is
taking the opportunity to expand its
inventory, operations and distribution
centre. We look forward to see what
they plan to do next.
SC
Australia's electronics magazine
Compatible with PB1004
10A continuous (20A peak),
72V
Connectors: solder pins on
a 14mm grid (can be bent
to a 13mm grid)
IC1 package: MSOP-12
Mosfets: TK6R9P08QM,RQ
5mm pitch SIL (SC6852, $30)
Compatible with KBL604
10A continuous (20A peak), 72V
Connectors: solder pins at
5mm pitch
IC1 package: MSOP-12
Mosfets: TK6R9P08QM,RQ
mini SOT-23 (SC6853, $25)
Width of W02/W04
2A continuous, 40V
Connectors: solder
pins 5mm apart
at either end
IC1 package: MSOP-12
Mosfets: SI2318DS-GE3 (SOT-23)
D2PAK standalone (SC6854, $35)
20A continuous, 72V
Connectors: 5mm screw
terminals at each end
IC1 package:
MSOP-12
Mosfets:
IPB057N06NATMA1
(D2PAK)
TO-220 standalone (SC6855, $45)
40A continuous,
72V
Connectors:
6.3mm spade lugs,
18mm tall
IC1 package: DIP-8
Mosfets:
TK5R3E08QM,S1X
(TO-220)
See our article
in the December
2023 issue for more details:
siliconchip.au/Article/16043
siliconchip.com.au
ASK SILICON CHIP
Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line
and we’ll answer your question. Send your email to silicon<at>siliconchip.com.au
Is it OK to use a higher
voltage capacitor?
This is probably a dumb question,
but can I use a 10μF 50V non-polarised
capacitor in place of a 10μF 16V capacitor for the Mk2 Bench Supply? (B. P.,
Scottsdale, Tas)
● Yes, that will work. You can
almost always safely use a capacitor with a higher voltage rating than
the one specified. The voltage rating
is simply the highest voltage that the
capacitor can be safely charged up
to. You can also use a non-polarised
capacitor when a polarised capacitor
is specified, although they are usually
larger and more expensive.
Query on Australian
manufacturing
On page 42 of the August 2024 issue,
at the top of the page, there is a photo
of two men next to a panel van. The
bloke in white overalls is named as
Ian Hyde. Would he be the same Ian
Hyde that designed and built the Tara
Systems Australia telephone and radio
access equipment for two-way radios
in the 1980s?
I used and installed the Tara 2020
unit in the local fleet of taxis in Gunnedah, NSW. It was a brilliant and very
reliable unit that was in service for 18
years non-stop. I believe Ian Hyde is
now retired and living in Bateau Bay,
on the NSW Central Coast. (P. H., Gunnedah, NSW)
● Kevin Poulter replies: I believe
you are correct. Ian’s email address is
in one of my mothballed old computers, so I would need to resuscitate it
to confirm. He certainly was a leading
identity at Pye and it’s great that the
system lasted so long.
Another well-known person from
Pye Telecommunications is Angus
Dawes, from the Export department.
He wrote a significant amount about
Pye in the 1950s onward and worked
together with Ian Hyde at the 1956
Olympics, providing services like
radio-telephone connection between
siliconchip.com.au
the Royal Yacht Britannia and Prince
Philip.
They worked from a ‘dream’ location in the MCG, a tech room with the
best view of the Olympics, plus the
essential bar fridge!
ESP32 board profile
changes break code
I have purchased an ESP32-CAM
module (February 2024; siliconchip.
au/Article/16129) and also the WiFi
BackPack kit (April 2024; siliconchip.
au/Article/16212). I am trying to get the
camera module to function first with
your software that I have downloaded
from the website.
I opened the sketch in the Arduino IDE and downloaded the ESP32
board profile from Espressif for the
AI Thinker. I have confirmed connection with COM4 and the correct baud rate for the CP2102 serial
device as described in the article.
The buttons are set up as Fig.2 in the
article. I tried to upload the sketch
several times and keep getting these
error codes:
app_httpd.cpp: In function
‘void setupLedFlash(int)’:
error: ‘ledcSetup’ was not
declared in this scope; did
you mean ‘ledc_stop’?
error: ‘ledcAttachPin’ was not
declared in this scope; did
you mean ‘ledcAttach’?
It doesn’t seem to be able to complete the upload to get the camera to
a point where I can log in to it. Maybe
there is a simple step between this and
doing that I am missing. Can you offer
any assistance to get me back on track
with this project? (G. W., Wellington,
New Zealand)
● This is almost certainly due to a
‘breaking’ version change of the ESP32
board profile. We used version 2.0.13
of the board profile (as noted on p66
of the review article), while the latest
version (at the time of writing this)
is 3.0.4.
According to the Releases page
Australia's electronics magazine
(https://github.com/espressif/arduino-
esp32/releases), there are several
changes between V2 and V3 that will
break existing code; see siliconchip.
au/link/ac0x
That page notes that the ledcSetup
API has been removed, which would
explain the errors you got.
The quickest and simplest fix is to
change to using version 2.0.13 of the
ESP32 board profile in the Arduino
IDE. The Arduino Boards Manager has
an option to install a specific version.
There should be a drop-down menu
with a list of available versions.
While you try that, we will see if it
is possible to update the ESP32-CAM
BackPack software to suit the latest
board profile.
Miniature oscilloscope
wanted
I have been reading through old copies of R&H, RTV&H and EA. I came
across a pen-sized oscilloscope (the
OsziFOX) on page 84 of Electronics
Australia, August 1999. Has Silicon
Chip ever designed something like
that? While I accept the limitations, it
seems a really handy tool. (J. R., Wellington, New Zealand)
● We have published a few handheld Test Tweezer type tools, but our
Advanced Test Tweezers design from
February & March 2023 (siliconchip.
au/Series/396) is probably the closest
to the OsziFOX as it has an oscilloscope mode. The Advanced Test Tweezers have a 128×64 pixel OLED screen
and run from a 3V coin cell, making
them considerably more capable than
the OsziFOX.
Having said that, the OsziFOX
would have been incredible to have
in 1999!
Replacing a motorised
pot with the Digital Pot
I would like to retrofit the Ultra
Low Noise Stereo Preamp (March &
April 2019; siliconchip.au/Series/333)
with the Digital Potentiometer (March
October 2024 109
2023; siliconchip.au/Article/15693). I
plan to:
1. Remove the motorised pot.
2. Remove the H-bridge and associated parts.
3. Omit the IR receiver from the digital pot board.
4. Supply the digital pot from the
power connector on the preamp.
5. Wire the digital pot input, output
and GND in place of the motorised pot.
6. Link the IR receiver on the preamp to pin 1 of JP1 on the digital pot.
7. Tie AN3 of IC5 on the preamp
board high to ‘trick’ the PIC into thinking the motorised pot is at the end of
its travel (for an ‘instant’ mute).
Does this approach make sense?
Should I use a resistor rather than a
link to tie AN3 high? Do I need to feed
it with a voltage lower than 5V, since
it typically expects to see 0.4-0.5V
depending on the current through the
pot motor?
I think the ACK and MUTE LEDs
on the preamp will still make sense
to the user since the two PICs will
be decoding and responding to the
same signal.
The digital pot has 10dB gain. Do
I need to somehow attenuate the signal to compensate? If so, where in the
signal chain would be best to do this?
It occurs to me that the PIC on the
low noise preamp could be reprogrammed to drive the digital pot IC
directly by repurposing the GPIO used
to drive the H-bridge. But that would
be considerable more work. (L. S.,
Kambah, ACT)
● What you propose seems good. It
would be wise to connect AN3 of IC5
via a 1-10kW resistor to 5V rather than
directly to limit the current and prevent the input going more than 0.3V
above Vdd. It does not matter that the
voltage is above the 0.4V expected
from the motor current detection circuitry. The ACK and Mute LEDs would
act as normal.
We suggest you change the first op
amp on the preamp board to be unity
gain by removing the 2.2kW resistor
to ground and replacing the feedback
components with a wire link, given
that the digital pot can provide gain.
Your remark about rewriting the
code for microcontroller IC5 makes
sense. However, that would be a lot
more work and code would also need
to be converted from the newer PIC
used in the Digital Pot, which can
be a troublesome process. Given the
110
Silicon Chip
relatively low cost of the chips, and
the fact that the two projects have been
tested separately, we think you should
keep the two chips.
How to program RPi
without an OS
I want to develop software that
needs the exclusive use of a microcomputer like the Raspberry Pi; in other
words, I would like to program it at
the ‘bare metal’ level. My understanding of bare-metal development is that
it demands much low-level groundwork to use a machine’s devices and
peripherals.
I was fortunate to stumble on Ultibo
(https://ultibo.org), which provides a
platform where much of the low-level
foundation is provided. It allows the
developer to relatively easily build a
single, machine-dedicated application
on top of that.
However, I’m not sure how much
support Ultibo receives. I suspect it
has received no attention for the last
two years. This is a concern if wanting to start a long-term development
using the tool. Are you perhaps aware
of any similar development platforms?
(A. J., Mindarie, WA)
● We hadn’t heard of Ultibo but it
is an interesting idea. According to its
GitHub repository, there was activity
as of two months ago (https://github.
com/ultibohub/Core), although a lack
of recent releases means the more
recent (eg, Pi 5) boards may not be
supported.
It certainly would be a lot of work to
program a Raspberry Pi from scratch.
Still, underneath it is just an ARM
processor, like so many microcontroller boards.
We found one example showing a Pi
3 being used to run a ‘blink’ program
on the bare metal (https://github.com/
dwelch67/raspberrypi). Of course,
any microcontroller should be able
to do that.
It will really come down to what
peripherals/features you need to use
and why it needs exclusive access (eg,
for security or real-time requirements).
If we had such a need, we would
investigate running the software on a
‘lite OS’, such as a console-only Linux
distribution. Many operating systems
provide a so-called ‘kiosk mode’ to
allow single applications to run without allowing user access to the underlying system.
Australia's electronics magazine
Distributions like RetroPi (which
turns the Pi into a dedicated game console emulator) could be another good
starting point.
For both of these, access to the
peripherals would be much like that
available on standard high level operating systems.
You could also consider using an
x86-based single-board computer, as
there is plenty of x86 support available.
We have published two projects
using a Raspberry Pi with a dedicated application: the Raspberry Pi
Tide Chart (July 2018; siliconchip.au/
Article/11142) and the Speech Synthesiser (July 2019; siliconchip.au/
Article/11703). Both are fairly secure
in that the user inputs do not provide
an easy way to access the underlying
operating system.
Is the Analog Clock
beginner friendly?
I haven’t really done any soldering
before but I have invested in a decent
soldering iron and I have a basic oscilloscope and DVM. As more-or-less a
beginner to soldering, would I likely
be successful in making the new
GPS Analog Clock Driver using your
SC6472 kit? (E. M., Hawthorn, Vic)
● As a beginner, you may find soldering IC3 and the USB socket (CON4)
difficult. We strongly suggest you
acquire a syringe of flux paste if you
don’t have one, as it makes soldering
those parts much easier. A fine-tipped
soldering iron would help, along with
some solder wick, to remove solder
bridges. You could practice soldering the other components first before
tackling those.
So long as you are careful and can
see the area for soldering well enough
(a magnifying lens would help), it
should be possible. Having said that,
it is a bit difficult to predict whether
this project is achievable for you. You
could consider building the SMD
Trainer kit (SC5260) first.
Trying to compile older
PIC C code
I have used MPLAB X assembly
language extensively but not the C
language.
I downloaded the source code for
your High Visibility 6-Digit LED GPS
continued on page 112
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WARNING!
Silicon Chip magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects
should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried
out according to the instructions in the articles.
When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC
voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages,
you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone
be killed or injured while working on a project or circuit described in any issue of Silicon Chip magazine.
Devices or circuits described in Silicon Chip may be covered by patents. Silicon Chip disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. Silicon Chip also disclaims any liability for projects
which are used in such a way as to infringe relevant government regulations and by-laws.
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siliconchip.com.au
Australia's electronics magazine
October 2024 111
Advertising Index
Altronics.................................35-38
Blackmagic Design....................... 7
Dave Thompson........................ 111
DigiKey Electronics....................... 3
Emona Instruments.................. IBC
Hare & Forbes............................... 9
Jaycar............................. IFC, 59-62
Keith Rippon Kit Assembly....... 111
Lazer Security........................... 111
LD Electronics........................... 111
LEDsales................................... 111
Microchip Technology.............OBC
Mouser Electronics....................... 4
PMD Way................................... 111
SC Ideal Bridge Rectifiers......... 108
Silicon Chip Back Issues......... 103
Silicon Chip Binders................ 111
Silicon Chip PDFs on USB......... 80
Silicon Chip Shop...................... 95
Silicon Chip Subscriptions........ 81
TME............................................. 11
The Loudspeaker Kit.com.......... 10
Wagner Electronics....................... 8
Notes and Errata
Automatic LQ Meter, July 2024:
a few constructors had problems
with IC1 (OPA2677) oscillating,
making it hot and causing
excessive current to be drawn
from the battery. Some have
solved it by replacing diodes D1
& D2 with some from a different
batch or by adding a 220Ω resistor
in series with diode D1 (see
Mailbag, September 2024, page
10). A better solution is to replace
IC1 with an OPA2890 op amp. If
you bought a kit and have this
problem, contact us to request an
OPA2890.
Next Issue: the November 2024
issue is due on sale in newsagents
by Monday, October 28th. Expect
postal delivery of subscription
copies in Australia between October
25th and November 13th.
112
Silicon Chip
Clock (December 2015 & January 2016;
siliconchip.au/Series/294) and set up
MPLAB X v5.50 and the current XC32
compiler. It appears that Microchip no
longer includes the plib.h, math.h and
string.h headers with the compiler.
Can you tell me what version of
MPLAB and the XC32 compiler you
used when you developed the clock?
The code is in a folder called LED
Clock.X, which suggests that the IDE
was some version of MPLAB X. Starting with v5.35, it wanted to upgrade
the file, so I worked backwards to v4.20
which didn’t.
Having found those headers, I got
a heap of other errors when I tried
to compile the code. I think it might
be better if I use the same version
of the software you did originally.
Some lines in the code that are particular problems are calls to assembler
instructions such as:
asm volatile (“eret”);
There is a similar line with the
“wait” instruction. Do I have to do
something in Project Properties to get
these lines to compile/assemble? The
error message is:
“C:\Program Files (x86)\
Microchip\xc32\v1.31\bin\
xc32-gcc.exe” -x c -c
-mprocessor=32MX170F256B
-ffunction-sections -mips16
-Os -fomit-frame-pointer
-DSHOW_UTC_FEATURE=1 -MMD -MF
build/default/production/
sleep.o.d -o build/default/
production/sleep.o sleep.c
-DXPRJ_default=default
-legacy-libc -mno-float
-G2048
C:\Users\Gjc\AppData\Local\
Temp\cciHwjKm.s:133: Error:
unrecognised opcode `wait’
(G. C., Mount Dandenong, Vic)
● You are right that they are no
longer packaging those older libraries
with XC32. This page on the Microchip
website explains where to get plib.h
and the other headers: siliconchip.au/
link/abyw
It is now a separate download on
the same page where you get the compiler. “math.h” and “string.h” are part
of the standard C library, so we are surprised they are not included with the
compiler. The above download may
include them as well.
The build logs in the software
download package show that the
Australia's electronics magazine
compiler used was XC32 v1.31. It
should be possible to get it to compile with the latest XC32 with some
fiddling (basically downloading and
installing headers), but you are right
that it might be easier to go back to
that earlier version.
We wonder if the “unrecognised
opcode” error is related to the -mips16
option. We suggest you try switching
off the MIPS16 option for that file;
you can do it in the IDE on a file-byfile basis.
MIPS16 is a more compact instruction set, and we used it because the
code wouldn’t fit into the available
flash memory otherwise. However, it
doesn’t seem to include the wait or eret
instructions; those appear to be part
of MIPS32 only. We suspect the compiler used to detect that and switch to
MIPS32 mode to execute those instructions, but it may no longer do that.
The strange thing is that the code
obviously compiled for us back in
2015, even though we were using the
same version of XC32 (v1.31) as you.
Perhaps it has something to do with
the IDE providing the compiler with
a different set of option flags.
Without the MIPS16 flag, the compiled objects will likely be a little
larger, but we don’t think they all need
to be MIPS16 for the software to fit in
the chip. So you might be able to get
away with switching just those problem files back to MIPS32 mode.
Information wanted on
EA project
I am looking for the original article
for the Xenon Strobe Timing Light
project that used a Dolphin torch
for the reflector and housing. I built
one when I was younger. It was published approximately between 1980
and 1982; I seem to remember it was
either in the Electronics Australia or
ETI magazine.
Looking through EA issues between
1979 and 1982, I found the Digital
Tacho/Dwell meter and the Transistor-
Assisted Ignition projects that I built
around the same time, but not the
Strobe. (S. R., via email)
● The only project we can find in
EA or ETI that used a Xenon flash tube
in a Dolphin torch reflector is the Digital Strobe project in EA, March 1986
(starting on page 42). However, it is a
strobe and not a timing light, as it isn’t
triggered by an ignition system. SC
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