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The origin of Presspahn
If anyone ever wondered where
Presspahn insulation comes from, it’s
here in Yorkshire – God’s own county,
of course! You can see the location of
the factory at the following link.
siliconchip.com.au/link/ab8e
Alan Winstanley,
PE Magazine Online Editor,
Brighton, UK.
Transistor Test Set identified
The “TRANSISTOR TEST SET”
shown in the photo on page 4 of the
May 2021 issue is an Electronics Australia project from August 1968, presented by your own Jim Rowe. I built
one of these at the time and still use it.
It’s a very useful piece of equipment.
As to the “ACE” on the meter face,
I think this refers to a company called
ACE Radio, a regular advertiser in EA
at the time. They appear to have sold
mostly surplus items, but also kits for
some EA projects, the Transistor Test
Set being one of them. It was available as either a fully built item, or as
a DIY kit.
Peter Caprin,
Valley Heights, NSW.
it did nothing for a few turns; then it
started to rise, very slowly at first, then
exponentially faster.
After a good half an hour of adjustment, I could get it to hover around
6V and would hold there for about
thirty seconds or so, then very slowly,
it started rising again, getting faster
and faster. To keep the voltage below
8V, I had to wind the trimpot anticlockwise two or three turns, which
started the voltage decreasing, and it
continued doing so until it was under
1V. I couldn’t get it to hold at 6V.
That stumped me, so I decided to
finish building the second module,
and was surprised to find that it had
the same unstable quiescent current. I
figured the problem wasn’t the SC200
modules but something in the power
supply, although it was testing fine.
As I was clutching at straws, I
started wondering if the leads from
the power supply to the amp modules
were picking up EMI as I had extended
them with some leftover hook-up wire
(about one metre long) to make adjustments easier.
So I cut the extensions off and fitted the power supply wires properly,
and that cured the problem. I adjusted
the quiescent current and offset as per
instructions. The amp is now working
perfectly, and (to our ears) my wife,
daughter and I all agree that music
sounds clearer, more precise and the
bass is much more potent than the old
ETI modules, with no hum.
I wouldn’t have believed the difference in sound quality could be so evident between the two.
Tony Brazzle,
Bumberrah, Vic.
Comment: based on the symptoms you
described, we would not have guessed
that it would be the power supply wiring at fault. It sounded more like a case
of mismatched transistors. We’re glad
you managed to sort it out, and your
listening tests confirm what our test
equipment shows – that the SC200
modules are high-performance modules, only falling short of the very best
amplifiers, like our Ultra-LD series.
Expanding the Remote
Monitoring Station
A huge belated thank you for the
article on the Arduino-based 4G
Remote Monitoring Station from the
SC200 audio amplifier
problem solved
While trying to set the quiescent
current of the SC200 amplifier module
I had just completed (January-March
2017; siliconchip.com.au/Series/308),
I ran into a strange problem. Everything tested fine up to the point of fitting the 68W resistors in place of the
fuses. Feeding a signal into the module produced a clean waveform on the
scope at the output.
The problem I had was some sort of
funny runaway effect happening while
adjusting the voltage across the 68W
resistors to the 6V specified. With the
trimpot turned fully anti-clockwise,
the voltage was just under 1V, which
was correct. As I wound it clockwise,
4
Silicon Chip
Australia’s electronics magazine
siliconchip.com.au
February 2020 issue (siliconchip.com.au/Article/12335).
I decided to take your design and expand on it.
Attempting to learn a new language and learn the inner
details of the SIM7000 module at the same time may not
have been the easiest choice. Learning a new language
meant I spent a lot of time undoing the good work of
Silicon Chip, only to put it back later.
I have a water pressure sensor to monitor for stock water
for cattle. The electric pump is 10km away from home. A
no-pressure situation will eventually lead to no water for
thirsty cows, especially in the summer months.
On power-up, it sends me a text message indicating
the firmware revision and the pressure level. An SMS is
generated should the pressure go outside a preset range
at any time. I can also make a query by sending a “q” or
“Q” to the remote Arduino.
The water pump will stop if AC power is lost for more
than a few seconds. Manual intervention is required to
reset the pump. The Arduino/SIM7000 restarts when
power is restored and sends a text message. This is my
cue to go to the pump.
Before installing the Arduino/SIM7000, this required a
visit to the pump or checking if water came out of one of
the float valves. The latter is never fun in the winter, as it
requires one’s arm to be immersed in the water.
I obtained the gravity water pressure sensor by DFRobot
(SEN0257) from Core Electronics. It has a BSP thread. I cut
off the supplied connector and fitted a three-way Deutsch
DT connector to provide a degree of weatherproofing. I
doubled up the supplied wires for the crimp contacts.
The SIM7000E is no longer sold by Core Electronics
but can be obtained directly from DFRobot (www.dfrobot.
com/product-1732.html).
As I do not require the GPS or air pressure sensor functions of the SIM7000 card, I removed the associated code.
I also modified it as I did not require the power-saving
shield. I then housed the system in a waterproof enclosure from Jaycar.
I used the following links to confirm that the SIM7000E
was compatible with my local tower: https://whirlpool.
net.au/wiki/mobile_phone_frequencies
www.stelladoradus.com/finding-my-frequency-onmy-iphone/
The CAT-M frequency bands supported by the
SIM7000E are B3/B5/B8/B20/B28. The band number of
my local tower was 3. I determined this using the notes
at www.stelladoradus.com
I then added several hard-coded commands to the code
to ensure that the SIM7000E is configured as I intended,
rather than taking a chance. I send the SIM7000E the following commands on power-up:
To set the preferred mode to LTE only (2 = Automatic, 13
= GSM only, 38 = LTE only and 51 = GSM and LTE only):
MODEM.println(“AT+CNMP=38”)
To set the band to CAT-M (the other choice is NB-IOT):
MODEM.println( “AT+CBANDCFG=CAT-M”)
To select CAT-M only (1 = CAT-M, 2 = NB-Iot, 3 = CAT-M
and NB-IoT):
MODEM.println(“AT+CMNB=1”)
Enables full phone functionality (there are six options;
1 is the default):
MODEM.println(“AT+CFUN=1”)
6
Silicon Chip
Information on these commands can be found in the
SIM7X00 Series_SMS_Application Note_V1.00 and
SIM7000 Series_AT Command Manual_V1.04 documents.
To test the SIM7000 thoroughly, I began sending it
photos to see if it would be robust enough to cope. This
did not go well; I would be interested from other readers
how they dealt with this sort of abuse dished out to the
SIM7000E. I had to keep the SIM7000E powered up for
over 24 hours and wait for the network to put things right
before it functioned normally again.
I am building my second monitor now. I will upgrade
the firmware in the future to monitor pressure trends and
the duty cycle of the mains-powered pump.
Ed O’Brien, Heyfield, Vic.
Comments on DIY Reflow Oven project
I’m building the DIY Reflow Oven controller (April-May
2020; siliconchip.com.au/Series/343) and have looked
back over the previous uses of the same control board
(eg, the DDS from February 2020; siliconchip.com.au/
Article/12341).
I am having a little trouble understanding the logic
behind the two regulator designs. Why is a low-dropout
regulator specified for REG2 that is quite expensive to buy
with delivery charges, rather than the readily available
LM317? After all, the LD1117V is rated at only 0.8A (instead
of 1A) and has far more voltage “headroom” than the 5V
regulator used for REG3. Could I use an LM317T instead?
Also, the data sheet for the LD1117V shows a recommended 120W value for the top resistor with the 10μF
capacitor, whereas 330W has been used instead – whilst
this may improve ripple performance, would it not also
degrade response times?
I know this project utilised a design from another application. Still, I wonder if a Micromite BackPack might have
been a better option – the touchscreen has higher resolution, and it would do away with the need for a separate
board, rotary encoder, cabling etc.
Also, using PWM on a leading-edge dimmer-type
circuit would put less thermal shock and stress on the
oven elements and might be a lot less expensive than
the solid-state relay.
As another observation, many people have difficulties
with soldering smaller SMDs. Yet, this board uses 2012
(imperial 0805) rather than 3216 (imperial 1206) parts
with 3226 (imperial 1210) pads, for example – that would
be much easier to deal with.
The board is obviously very heavily packed, with very
little clearance between parts – this caused me some problems; for example, the 100nF X7R 2012 capacitors are less
readily available (unless in large quantities), and I had to
fit 3216 parts onto the rather small pads.
Also, many of the connectors are too close together
(although, with heavy trimming, I was able to fit a few
boxed headers that I prefer to avoid later connection mistakes). The specified flag heatsink does not fit due to connector and capacitor clearance issues.
I did manage to get the board together – without heatsink – but with the aid of Geoff Graham’s recommendation of a stereo microscope, and a spring-loaded stylus I
made to hold the parts in place for soldering. I am waiting for another part before commencing the testing phase.
Ian Thompson, Duncraig, WA.
Australia’s electronics magazine
siliconchip.com.au
Comments: In some projects, that controller board is powered from 5V DC, so the LD1117V is needed for a regulated 3.3V rail. You are correct that in the DIY Reflow
Oven, this board is powered from 9V DC, so you could
use an LM317 instead.
The advantage of the 120W resistor compared to the
330W resistor we’ve used is that it guarantees that the regulator’s minimum load requirement is met even if nothing
is drawing current from the regulator’s output.
However, other devices on the board constantly draw
current from the regulator’s output, so the lower value is
not needed. It won’t affect the response time.
Yes, the Reflow Oven could have been controlled using
a BackPack controller, but a third party contributor
designed this project, and he decided to re-use his existing controller design.
We didn’t think it was worth the effort to redevelop the
project to use the Micromite BackPack (even though we
would prefer that), given that it was presented to us as a
fully working, completed design.
We don’t consider 2012-size parts to be all that difficult to hand solder; they are not that much smaller than
3216 metric (being 1.2mm wide rather than 1.6mm wide),
and the pads tend to be a bit more generously sized in
relation to the parts. We usually avoid going any smaller
than that, although the next size down (1608) is not much
harder to manage.
We agree that the controller board for this project is
packed, although we were able to successfully build and
test it without having to trim anything. That includes the
heatsink, which we somehow managed to fit – perhaps
ours is a fraction smaller than yours.
Of course, different constructors will have different
skill levels and visual acuity, and we realised these
projects will be challenging for some. We publish a mix
of projects that use a wide variety of differently-sized
components.
You should not have trouble getting 100nF X7R
2012/0805 capacitors. They are a very standard item used
in the millions (if not billions). Element14 sells a variety
of suitable capacitors starting at around 3¢ in quantities
of 10+ (cat 1759166), while RS sells them for 9.7¢ each
in quantities of 100+ (cat 135-9033).
One hundred might seem like a large quantity to purchase, but considering how many 100nF bypass capacitors
are in the average design, and the fact that 2012 capacitors will usually comfortably fit on 3216 pads, we think
it’s worthwhile to stock up on them.
Dodgy switches becoming common
The Serviceman’s Log entry in March 2021 about G.
C.’s problem with a membrane switch on a coin counter
prompted me to write in. I recently came across several
faulty switches, and am beginning to think that they are
getting poorer and poorer.
The first one was a switch on an electric chainsaw that
used to weld up and not switch off. I stopped using the
chainsaw for that reason.
Later, I came across an old switch that has the quick
on/off function - no matter how slowly you operate the
switch, it changes over really fast, and it has big contacts.
I managed to fit this to the chainsaw, and that was the end
of that problem.
siliconchip.com.au
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June 2021 7
Helping to put you in Control
Mini Temperature & Humidity Sensor 0-10V output
The Pronem mini from Emko Elektronik are
microprocessor based instruments that incorporate
high accurate and stable sensors that convert
ambient temperature and humidity to linear 0 to
10VDC. Dimensions are only 40x 79 x 16mm.
SKU: EES-001V
Price: $149.95 ea
Modbus TCP Analog Output Module
The analog output module MU110-501 has 8
analog outputs (0/4-20 mA, 0-1/10V). Support for
Modbus TCP, MQTT, SNMP, SNTP.
SKU: AKC-263
Price: $545.95 ea
Proop 7 Control 7” HMI with 2 Ethernet Ports
This is a budget priced Touchscreen with
a resolution 800 x 480 pixels and 260K
colors; Ethernet, WiFi, RS-232 and RS-485
communication and 8 digital inputs/outputs for
control.
SKU: EEI-012
Price: $619.95 ea
Digital ON/OFF Temperature Controller
DIN rail mount thermostat with included PTC
sensor on 1.5m m lead. Configurable for a huge
range of heating and cooling applications. 230
VAC powered.
SKU: EEC-010
Price: $89.95 ea
Isolated Load Cell 2mv/V 0-10V Transmitter with Display
Converts a signal for a 2 mV/V load cell to a 0 to
10 V signal. Able to power 2 load cells in parallel.
DIN-rail mount.
SKU: ALT-415
Price: $249.95 ea
LabJack T7 Data Acquisition Module
LABJACK T7 Multifunction DAQ with
Ethernet, wifi and USB. Features 14
analogue inputs, 2 analogue outputs
and 23 digital I/O
SKU: LAJ-045
Price: $739.30 ea
Ultrasonic Wind Speed & Direction Sensor
RK120-07-AAC Economical Ultrasonic Wind
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RS485 output and 4 metre cable. 12~24VDC
powered.
SKU: RKS-028M
Price: $499.95 ea
For Wholesale prices
Contact Ocean Controls
Ph: (03) 9708 2390
oceancontrols.com.au
Low-cost buck/boost module warning
Prices are subjected to change without notice.
8
Silicon Chip
The second one was the remote control for my garage
door. Since new, the button always required a few presses
before the door opened. Then it stopped working altogether.
I took it down to the workshop and split the case open
to check the battery (two 3V button cells). They tested
OK, so I removed the PCB. The first thing I tested was
the continuity of the pushbutton switch. When pressed,
it remained open circuit.
I had some good quality push button switches, but they
had a much higher profile, so I installed one of these and
cut a hole in the case to accommodate it. The remote not
only worked fine after that, but now only needs one press
of the button to open the door.
The final switch problem was with an auto-darkening
welding helmet. I had been using it for some months
when it became unreliable. I put a new 3V button cell
in it, but that made no difference, and after getting a few
more flashes while using it, I tossed it aside and went
back to my old faithful.
A medical problem put me on light duties for a while,
and while wondering what to do with myself, I thought
I would have a look at the faulty helmet. These helmets
have a shade adjustment on the side with a grind position, which I wished was not there, because if you put the
helmet down a certain way, it turns the knob onto grind,
giving you a flash.
When adjusting the shade on the auto-darkening filter
(ADF), the screen used to flicker, which I put down to a
noisy potentiometer. So I thought that was a good place
to start. The ADF cartridge is made to be removed easily
to facilitate the replacement of the front cover lens. The
switch is removed by pulling off the knob and undoing
the nut behind the knob.
With it on the workbench, I prised up some plastic tabs
and removed the cover to reveal an ordinary pot with a
switch on the back. I was going to substitute another pot,
but as it was easier to test the switch, I did that first.
With the control in grind position, the switch was open,
and I measured some volts across it. When I turned the
pot to the darkening position, I got a reading of 1.2V. I had
expected a lot lower than that, but the ADF worked fine.
However, when I turned the control further, the voltage
ranged all over the place, going as high as 1.6V, and the
ADF did not work.
As I needed little excuse to do away with the grind position, I simply soldered a piece of wire across the switch
terminals. It was easy to put back together, reversing what
I did to take it apart.
I have used the helmet for some months now, and I
have not had a single flash. Not only that, but the shade
control gives a smooth change over the whole range with
no flickering. Also, I have been able to adjust the other
settings more precisely to suit me. I am very pleased with
the result.
It worries me just how many of these devices are
scrapped just because of poor-quality switches.
Ron Groves, Cooloola Cove, Qld.
I am writing about the “Reliable solar lighting system”
circuit published in the Circuit Notebook column of the
January 2021 issue (siliconchip.com.au/Article/14711).
Australia’s electronics magazine
siliconchip.com.au
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FEBRUARY 2021
37
The circuit shows a solar panel with a nominal 12V output feeding what is described as an “XL6009 based buck/
boost converter module” producing a 5V output.
Converter modules using the XL6009 IC are readily
available from numerous vendors online. On paper, these
modules are very attractive, with wide input and output
voltage ranges.
While some XL6009 modules are single-mode only
(buck or boost), some offer automatic changeover depending on the input supply, guaranteeing a fixed output voltage regardless of whether the input is above or below the
preset output voltage. Such modules can be identified by
the presence of two inductors, rather than the one used
in the fixed-mode modules.
There are pitfalls with the XL6009, however. Despite
websites having descriptions to the contrary, according to
the manufacturer’s data sheet, the minimum input voltage
of the XL6009 is 5V. So it is not guaranteed to produce a
regulated output voltage when the input drops below 5V.
Usually this would be of little consequence, but there
is a flaw with the XL6009 which, depending on how it’s
used, could end up destroying the device it is powering.
Within a certain range of input voltages under 5V, the output rises many times higher than the set output voltage.
For example, on the multi-mode module I tested with
its output set to 5V, the fault occurred with input voltages
between approximately 3.0V and 3.2V. Output voltages
ranging from 14V up to 51V were produced, and adding
a load resistor showed that non-trivial currents could be
supplied when the high output voltages were present.
Obviously the XL6009 does not contain a low voltage
cut-off circuit, which it needs given this behaviour. The
fault could be triggered by a slowly rising input voltage
(eg, when light is applied in the early morning to the solar
panel mentioned above), or if something such as a flat battery prevents the input voltage from rising high enough
to guarantee correct operation.
It could be that the TP4056-based LiPo charger used
in the “Reliable solar lighting system” is not adversely
affected by short bursts of very high voltages on its
input. Alternatively, perhaps the solar cell cannot supply sufficient current at voltages in the critical range to
do damage.
If this is the case, then the immunity of the described
circuit to the XL6009 problem is due mainly to good
luck. However, if anyone is tempted to use the XL6009
to power something more sensitive (such as a Raspberry
Pi or Arduino board), this fault with the XL6009 could
end up destroying the board.
I was planning on using a dual-mode XL6009 module to
power a Raspberry Pi board, but decided to thoroughly test
the module first. It was while smoothly varying the input
voltage that I noticed a sudden jump to over 50V on the
output, which prompted a more careful investigation. As a
result of this observation, I will never use anything based
on the XL6009 – the IC is simply not reliable.
While an external low voltage cut-off circuit could mitigate the problem, the XL6009 still has its potentially devastating problem, and I am not willing to chance it with
anything of value.
More recently, I discovered that others have encountered similar issues with XL6009 modules; see https://
owenduffy.net/blog/?p=12435
10
Silicon Chip
Australia’s electronics magazine
siliconchip.com.au
I think it is worth warning your readers of this serious
problem with the XL6009 and modules which use it.
While such modules appear to be very useful in theory for
various situations, in my opinion, they are best avoided.
Jonathan Woithe, Valley View, SA.
Strange capacitor value readings
For the second time, I have had the curious situation
where several capacitors do not measure as their stated
value, but all return almost the same capacitance. Over a
year ago, I measured the 200V 330μF main capacitors in
two PC power supplies. All four returned a value close to
220μF. The supplies were the same brand, and the capacitors the same manufacturer.
More recently, I checked three identical 440VAC 10μF
power factor correction capacitors from mercury arc control units. They were made in 1981, and all three tested
at about 6.5μF. If there is anything wrong with these, it
is not showing. I charged them to 40V, and after an hour,
they still measured over 20V, with most of the discharge
due to the DVM.
This makes me suspect that the manufacturers incorrectly marked the capacitors. I just cannot think of a reason why they would similarly decrease in value. I did
verify that the capacitance meter was reading correctly.
George Ramsay, Holland Park, Qld.
Comment: we suspect that these are from ‘bad batches’
of capacitors that had some sort of variation in their
manufacturing process or inputs, causing them to all
have similar capacitance deficits.
Or they could have been fraudulent; lower value
capacitors altered with higher values to be sold at a premium (perhaps with a few ‘good ones’ on top to avoid
suspicion).
Digital Insulation Meter displays incorrect values
I have just finished building Jim Rowe’s Digital Insulation Meter (June 2010; siliconchip.com.au/Article/186)
as a “rainy day” project. I now have it up and running. I
have pretty much followed the published circuit diagram;
however, I built my own PCBs using a slightly different
layout to accommodate a different LCD screen (the 1602A
type) than the one used in the article.
My meter appears to be working correctly, producing
close to the correct test voltages and, pleasingly, displaying
on the LCD close to the right leakage current and resistance
measurements for known test resistor values of 10MW
and 1MW. On the 500V setting, when the test button S2
is pressed, I obtain the following results on the LCD: Ix =
49μA, R = 10MW and Ix = 0.4mA, R = 1MW respectively.
However, when test button S2 is released, the LCD then
displays Ix = 16μA, R = 30MW and Ix = 1μA, R = 260MW
for the 10MW and 1MW test resistor values, respectively.
These values don’t appear to have much meaning, and I’m
wondering if they’re correct as they create some confusion.
Upon releasing S2, I expected the LCD to return to displaying something like the screen “Set Volts, Press button
to Test:” that initially comes up on powering up the meter.
I changed the code to behave this way by adding a
couple of extra instructions in the program’s main loop
to ensure that the current and resistance readings on the
LCD are blank between measurements, ie, when switch
S2 is released.
siliconchip.com.au
I’m not sure if this was what Jim originally intended,
but it makes more sense to me, and it was a simple fix.
An extract of the code follows, with the added instructions highlighted in red:
CALL InitDig
CALL SetVolts
BTFSS PORTA,4
CALL Display3
BTFSS PORTA,4
GOTO $-1
I’m now very happy with the performance of my Digital
Insulation Meter, so thanks to Silicon Chip for the great
project (from some years ago, but it’s still very useful and
was fun and educational to build and modify!).
Stephen Denholm,
Howrah, Tas.
Comment: Jim did not experience the same problem as
you with his prototype, and we think it might have to do
with the characteristics of the button you have used or
some other detail of your build.
Regardless, your solution is a good one. The only disadvantage is that you need to make a note of the readings
before releasing S2.
The easiest way to cut your power bill
How can Bruce Pierson of Dundathu, Qld
doubt the claims of Voltex (Mailbag, May
2021, p10)?
I also have a device that I guarantee will
cut your power bill in half! It’s shown in the
accompanying photo. This versatile device
can also be used to cut you phone bill, water
bill, gas bill etc in half.
But seriously, it is a shame that nobody
is held to account for perpetuating
these obviously fraudulent claims/
sales. I imagine the people who fall
for these products are the ones least
able to afford them.
Ron Walker, King Creek, NSW.
Worshipping a greater power
The accompanying photo (shown below) is of a local
church that caught my eye. I guess you could call this
“Heavenly Power”!
SC
John Chappell, Caloundra, Qld.
Australia’s electronics magazine
June 2021 11
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