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and we’ll answer your question. Send your email to silicon<at>siliconchip.com.au
On Gerber files, FPGAs
and PID coefficients
I have just received my copy of the
October issue in the mail to find that
you plan a couple of things of particular interest to me. I like the idea of using a laser engraver to make a PCB, so
I am looking forward to that article.
Currently, I am looking at the Creality CP-01 from Altronics. But so far,
I have not found a unit that accepts
Gerber files, and thus the Gerber file
has to be converted to JPEG, and then
using a photo application to invert
positive to negative.
You have noted that you have not
published many articles on FPGAs,
and I think that is likely due to the
difficulty in soldering these devices
onto PCBs. Also, programming these
devices requires some expensive tools.
I would like to mention a possible
improvement to the thermocouple wiring on DIY Solder Reflow Oven Controller (April-May 2020; siliconchip.
com.au/Series/343). As you say, thermocouples are not that accurate, but
it depends on the class. For class 1 it
is ±0.5°C, and for classes 2 and 3, it
is ±1°C.
My suggestion is to obtain a type-K
plug and panel-mount socket and use
a short length of T/C cable cut off the
thermocouple to go between the socket
and T/C module. This eliminates the
multiple cold junction points, which
will not be at the same temperature due
to the layout of the components. It also
makes it just a bit more professional.
Be aware that there may be a lacquer
coating on the wire which needs to be
cleaned off, and that the fibreglass insulation may make your hands itch.
One thing on this unit is that the
PID coefficients don’t seem to match
what I know of standard PID settings,
as the D value is so high. Is there a
units change?
Lastly, I’d like to comment on the
Serviceman’s Log by Dave Thompson.
I am glad he managed to fix his analog
meter. It is lucky because the jewels in
meters are usually spring-loaded and
siliconchip.com.au
so all that happened was one jewel was
pushed down, enabling the other pivot
to pop out. Simple to fix.
What he could have had was one
of the hairsprings having been bent
so the coils touch each other, causing
calibration problems or worse, a bent
pointer. Both are fixable with great patience and care, but I won’t go into details on that. Please ask him if he has
experience with taut band suspension
meters such as the spot galvo. I’m not
sure if the AVO was that or had standard pivot and jewels. (W. D. K., Bayswater, Vic)
• You are right that you probably have
to convert Gerber files to an image
format for use with the laser engraver software. We cover all the steps in
that article, which is planned for the
December issue.
Many FPGAs are available on development boards these days, removing soldering from the equation (many
also come in quad flat packs which are
not all that hard to solder with some
practice). Software is becoming less of
a problem too; many types now have
free software available. We have covered these aspects in a couple of articles to date, and no doubt will have
more to say in future.
As for the thermocouple interface
for the Solder Reflow Oven, we agree
that adding proper thermocouple
adapters is definitely nicer. But the
cheaper and easier method described
in those articles is adequate for the
soldering task. There are substantial
temperature differences around the
oven, and a degree or two here and
there in measurement is less than this
variation.
As for the PID parameters, the units
used are not conventional; they are
references to counts of the interrupt
service routine (ISR). The PID loop parameters were tuned using an empirical approach. They are a compromise
that gives good-but-not-ideal performance in the reflow oven application.
Phil initially identified an appropriate value for P, which in a steady state
gave reasonable behaviour. With I and
Australia’s electronics magazine
D at zero, there is a latency in settling
that runs to many minutes. So he increased the I value to reduce the settling time. While this did not result
in temperature oscillations, overshoot
was observable, so the I value has been
chosen to achieve a reasonable settling
time with manageable overshoot.
The D value was finally tweaked
to reduce the overshoot. On considering your question, it might be that
a reduction in I and a reduction in D
would be better.
Some lights do not meet
electrical standards
I have an oyster light fitting that can
be clipped to a ceiling fan or be mounted as a ceiling light. There is no Earth
connection at all to the metal base, and
I am wondering whether this legal. I
have been a subscriber of you magazine for years and are still enjoying it.
(M. W., Murray Bridge, SA)
• Such luminaires are not legal as the
metal enclosure is not Earthed and
there is no Earthing of the fitting if it
has a metal connection for the lamp,
such as a bayonet or Edison screw.
According to the AS/NZ3000 wiring
rules, “A protective earthing conductor, connected to a terminal or suitably
insulated and enclosed, shall be provided at every lighting point. The exposed conductive parts of luminaires
shall be earthed.” (section 5.4.3 Lighting points).
Capacitors – more than
meets the eye
Have you published an article on
capacitors? It seems there is more to
these devices than meets the eye, and
I am curious about why certain types
are chosen for a specific application.
This was initially triggered by the observation of the use of ceramics and
green caps, then the rise and fall of
tantalum caps. However, a couple of
recent incidents have rekindled and
broadened my curiosity.
Recently, the circulation pump on
November 2020 107
our solar hot water service became
intermittent. The motor run capacitor was only a fraction of its rated capacitance when measured with a multimeter. Being out of town, I looked
for a temporary replacement from my
parts at hand.
An old power supply had a couple of
X2 capacitor rated at 250V and when
connected in series, gave a little more
than the required 0.8µF with the benefit of a theoretically increased voltage
rating. This combination was bigger
than the original but just fitted in the
motor, and brought back reliable operation for three weeks until a proper
motor run capacitor could be obtained.
So what is the difference between
the X2 caps and the motor run cap?
The web page at siliconchip.com.au/
link/ab5k gave me confidence that
X2s are suitable for mains use, while
siliconchip.com.au/link/ab5l has a
broader background which raises more
questions. For example, how does one
tell a polyester film and a polypropylene capacitor apart, given that they
look similar?
Finally, my son and I are trying to
build an indicator light for the electric fence. We had the idea that a neon
lamp in parallel with a capacitor that
was charged via an 8kV, 500mA diode
(UX-C2B) salvaged from a microwave
power supply and a 51kW resistor
might work as a “relaxation oscillator”.
Testing it, it flashes every 3-4 electric fence pulses, and it does not load
the fence energiser. However, I am
now curious about the best capacitor
to use. The trial used a 1µF polyester
(or is it polypropylene?) rated at 250V
from the same microwave switchmode
power supply that donated the diode.
(D. G., Koyuga, Vic)
• Capacitors are indeed a topic with
more depth than most people realise.
Unfortunately, we haven’t published
an in-depth article on capacitors, with
the possible exception of our August
2002 article on tantalum capacitors
(siliconchip.com.au/Article/6744).
Your problem is prevalent – many
motor failures are actually motor capacitor failures. These capacitors
must have quite high capacitance and
voltage ratings, especially motor start
capacitors. Hence, start capacitors are
usually some type of electrolytic, and
they don’t tolerate long-term hightemperature operation well.
According to Wikipedia (https://w.
wiki/fJj), motor run capacitors are gen108
Silicon Chip
erally polypropylene types as they
must handle current continuously.
Many X2 capacitors are also polypropylene, so provided they have a sufficient ripple current rating, they should
be suitable.
Some X2 capacitors are polyester,
and those should be OK too, again as
long as they can handle the current.
There is no apparent difference in the
appearance; you have to look up the
part code to see if it is polyester or
polypropylene.
X2 capacitors are definitely suitable for mains use. The X part of the
designation indicates that they are
suitable for being connected between
mains phases (eg, Active and Neutral). Y-class capacitors are suitable
for connection between Active and
Earth (they are required to fail opencircuit rather than short-circuit for
safety) but can also safely be used between phases.
X/Y-class capacitors can lose capacitance if abused (eg, exposed to high
voltage spikes or passing more current
than they are designed for). X/Y-class
capacitors which are designed to handle significant currents, at least in the
short-term, are sometimes referred to
as “pulse” capacitors.
We pulled up a data sheet for a randomly selected 2.2µF 275VAC X2 capacitor (Kemet R46KN422000P0M) to
check its ratings. It is rated to handle
just 250mA continuously at 50Hz, so
it would only really be useful for a motor of about 60W. They make a 10µF
version which is rated for more than
1A at 50Hz.
So it appears that the main difference between a motor run capacitor
and an X2 capacitor is that X2 capacitors are not designed to handle
significant currents at mains frequencies, while motor run capacitors are.
X2-class capacitors probably also have
slightly different construction to meet
their safety requirements.
For your electric fence indicator,
you want a low-leakage capacitor so
ceramic, polyester or polypropylene
should all be fine as long as they have
a sufficiently high voltage rating. Presumably, that is limited by the neon as
it will conduct at around 80V.
For a proper discussion on capacitors, we would have to explain the
many different ceramic dielectrics
(NP0/C0G, X5R, X7R, Y5V etc), along
with the many different plastic films
used (polyester, polystyrene, PET,
Australia’s electronics magazine
polypropylene), varying plastic film
construction methods, mica capacitors, electrolytic capacitors (aluminium, organic, solid, tantalum etc) and
much more!
Help fixing an Iamm
Multimedia Player
Years ago, I purchased an “Iamm HD
Multimedia Player Cinema & Opera
Juke Box” (model NTD36HD).
This unit has never operated correctly. I tried to get it running after
purchase, then put it aside and forgot
about it. I found it again recently and
thought what a waste it could not be
used. I wondered if any of your staff
or readers could be of any assistance,
as I have had no success finding anything useful on the web.
The hard drive is accessible via the
USB socket and a computer. But when
the unit is hooked up to a TV and audio system and powered up, it shows
its start-up screen and plays its startup ‘music’, then very briefly goes to
the screen displaying choices (movies,
photos and music). The screen quickly
goes blank, and the unit is effectively
dead, save for the whirr of the harddrive still spinning.
I have tried without success to find
where I can get the ‘firmware’ to reload it. Does anyone out there have
any experience with these multimedia players? (D. R., Goughs Bay, Vic)
• We do not have any experience with
that brand. Perhaps a reader can help.
Linear Bench Supply
voltage variations
I am building the 45V 8A Linear
Bench Supply from the October & November 2019 issues (siliconchip.com.
au/Series/339). I have gotten to the
point of the initial tests and calibrations before installing the main heatsink components, but some readings
seem a bit off.
The supply rails seem OK. The
A5 pin of CON6 reads around 2.9V,
which is under the 3-4V range suggested in the magazine, but the temperature reading when I plugged in
the display matched close enough to
a nearby thermometer.
I did the initial calibrations so that
TP5 measured exactly 15.6V and TP6
measured exactly 6V. TP1 and TP3
were both very close to 0V each.
TP2 measures -115.7mV which is
siliconchip.com.au
below 0V as the article suggested, but
TP4 is 12.1mV which is close to zero.
I did have a little trouble fitting IC4
as I haven’t done any SMD soldering
before, but after blasting it with hot
air and clearing the bridges, I tested
it in-situ and it seemed to be working. Is the 12.1mV reading anything
to worry about?
I have a little pocket oscilloscope
which I used to test the oscillators.
Pin 3 of IC3 was close to the 60kHz
but about 51% duty cycle. The -5V
rail was correct though.
The Fan PWMs have me a bit worried. Pin 1 of IC2 measures 260Hz
instead of the mentioned 280Hz, although it has an exact 50% duty cycle.
However, pin 7 was showing a voltage.
The displayed temperature was 30°C,
so I carefully used an ice cube to drop
the temperature back down to 25°C,
and I still saw around 3V on pin 7. If
it’s already on, does it need to drop
lower than 25°C to switch off? (S. B.,
Banyo, Qld)
• None of these readings concern
us. The 12.1mV at TP4 corresponds
to 16mA at the output, which is not
precisely zero, but doesn’t sound excessive. It’s below the threshold of the
meter readings.
The PWM frequency isn’t critical;
260Hz is fine. We suspect that variation in the thermistor resistances and
zener voltages mean your supply has a
different temperature response. Compare the waveform on pin 5 of IC5 to
the voltage on pin 6 (see the scope
grabs on p28-29 in the October issue).
If you see the duty cycle on pin 7 increase as the temperature increases, it
is working correctly.
You could try replacing the thermistor with a potentiometer (say 20kW, or
at least above 10kW) and try sweeping
it up and down to check the response.
Using a Micromite as
an audio scope
Do you have software or do you intend to write a program for the Micromite Backpack to be an X-Y vector
scope? I need to display the Lissajous
pattern of a stereo audio signal without tying up my CRO. (P. S., Mount
Pleasant, SA)
• Peter Mather has posted a twochannel timebase scope CFUNCTION
on the Back Shed Forum at www.
thebackshed.com/forum/ViewTopic.
php?TID=8077
siliconchip.com.au
It has a ~1MHz sample rate. He has
also posted the source code. A quick
glance through it suggests that the code
which draws the pixels as X/T and
Y/T could be combined to draw X/Y.
How RMS power is
determined
Thank you for your wonderful magazine, which I have been purchasing
and reading since 1987.
Concerning the Ultra-LD Mk4 amplifier project (August-October 2015;
siliconchip.com.au/Series/289), the
rated power is listed at 135W RMS
into 8W with ±57V DC supply rails.
The term RMS is generally used
to refer to voltage or current and not
power. Power (in the audio industry)
is simply the product of RMS volts
and RMS amps where the signal is a
sinusoidal wave.
With supply voltages of ±57V DC,
my calculations show that the maximum RMS voltage is 40.3V RMS (57
÷ √2). Hence the power would be
203W RMS (V2 ÷ R) into a resistive
load of 8W.
Even with a Vce(sat) max of 3V for
the output transistors used, it is difficult for me to see how the 135V RMS
is derived.
Are you able to shed alight as to why
the power rating is 135V RMS for this
superb amplifier? (J. D. S., Endeavour
Hills, Vic)
• You are right that the term “RMS
power” is confusing, but it is common. As described in Wikipedia at
the following link, “RMS power” is
the power measured or calculated
with a continuous sinusoidal signal
(ie, it’s calculated based on the RMS
sinewave voltage): siliconchip.com.
au/link/ab4o
We measure it by increasing the signal level until the point where distortion starts to rise, then measuring the
continuous power delivered at that
setting.
Your calculation ignores several
important factors such as the fact that
the output voltage cannot swing railto-rail (due to several factors, including the driver and output transistor
base-emitter voltages). Plus the supply
voltage will not remain at ±57V DC at
full load, and there will be significant
ripple on the supply rails, which will
lead to earlier clipping.
There are also losses in the output
transistors (as you point out), losses
Australia’s electronics magazine
in the output filter, losses in the wiring and tracks etc. In short, you have
to measure the real-world power delivery (or a very accurate simulation).
The music power is stated as being
somewhat higher than 135W as this is
a short-term measurement and so the
supply voltage will not sag as badly.
You could probably get 150W RMS
from this amplifier module, or perhaps a little bit more, with a larger
transformer and larger supply filter
capacitors which would both help to
reduce supply voltage sag and ripple
under load.
How much do precision
voltage references drift?
On many occasions, I have appreciated the value of the Simplified 10V
Precision Voltage Reference by Jim
Rowe (August 2014; siliconchip.com.
au/Article/7976). The IC is now six
years old, and my version still runs
happily on its original 9V batteries.
My question is: how significant is the
age-related degradation that has taken place?
Also, what would be the best and/
or most economical method to recalibrate it if necessary? Is there a better or
more accurate standard easily achievable? Thanks for the great magazine,
keep up the good work. (C. O. D., Adelaide, SA)
• Jim Rowe responds: It’s good to hear
that you have found the Precision Voltage Reference of use. Analog Devices
quote the ageing rate of the AD587 device as ±15ppm per 1000 hours, but
this figure of 1000 hours probably refers to hours of operation rather than
merely the passage of time.
So unless you have been using your
Voltage Reference continuously over
the last six years, I would expect that
it would still be very close to its original calibration.
As my original prototype has only
been used about two or three times a
year in the last six years, I thought I
would test it this morning with three
different reference instruments. The
readings I obtained were 10.001V,
9.999V and 9.9976V – with the last
figure from a Yokogawa 7562 bench
DMM which has itself not been recalibrated since 2010.
The testing was done at 16.3°C,
about 9°C cooler than the original testing temperature in 2014. This suggests
that your Reference is probably still
November 2020 109
quite accurate too, which is good news,
since it isn’t all that easy to recalibrate.
Adjusting Mosfet dead
time with a scope
Is there any way to set the dead time
on the Class-D amplifier module (November & December 2012; siliconchip.
com.au/Series/17) using an oscilloscope? (B. C., Albion, Vic)
• It would be possible to use a scope
to observe the Mosfets switching on
and off to help guide you in setting
the dead time to the optimal value.
But doing so is quite tricky as the
upper Mosfet in each pair is ‘floating’,
so measuring their gate-source voltages would require an isolated probe,
or a scope with individually isolated
channels.
An easier approach would be to insert a shunt in the ground connection
of each pair of Mosfets and monitor
the voltage across it. The dead time
setting is optimal when it is set as
short as possible without a large spike
in current draw during the transition
period, when one Mosfet switches off
and the other switches on.
You would need to break the track
and solder in a shunt, and given that
its value would need to be low, you’d
need a pretty sensitive scope or amplifier. But it could be done. And this
would have the distinct advantage
that it would take into account the
switch-on and switch-off delays of
each Mosfet, which cannot be determined by merely observing their gate
drive waveforms.
Output from photoelectric smoke alarms
Around 20 years ago, I built your
Smoke Alarm Control Panel project
(January & February 1997; siliconchip.
com.au/Series/149). The installation
has been running since then without
any hiccups, bar the replacement of a
couple of ICs and the power supply. I
check it annually.
A while back, I decided to replace
the aging Kambrook smoke detectors
with newer Quell detectors, namely
the Q946 ionisation-type detectors.
These appear to use an A5364CA
CMOS IC. The replacement was a fairly
straightforward exercise, and the new
detectors work as intended.
The problem I now have is that
Quell made available a different smoke
110
Silicon Chip
detector for the kitchen location,
which is a photoelectric type (Q301H).
I cannot figure out how to interconnect
the alarm output from this device to
the Control Panel. I would be grateful
if you can provide me with advice and
help with this issue, as I do not want
to have the kitchen area unprotected.
(H. B., Mt Kuring-Gai, NSW)
• The alarm output from the photoelectric smoke detector (Q301H)
should be available at pin 10 of the
A5364CA IC.
For the alarm test input, use the additional circuit of the Control Panel for
Smoke Alarms comprising Q4, except
using a 200kW resistor (instead of the
1MW resistor) at Q4’s collector. Connect the opposite end of the 200kW
resistor directly to the “push to test”
button.
Stopping nuisance
smoke alarms
Do you know of a clever way I can
turn off the smoke detector while cooking? Also, have you designed an aspect
ratio converter? I need to convert VHS
footage from 4x3 to 16x9 without using
a computer. (J. H., via email)
• We published a smoke detector kill
switch in February 1996 to prevent an
alarm when cooking: siliconchip.com.
au/Article/5038
We have not published an aspect ratio converter. There are commercially
available units such as the Miranda
ARC371P; we suggest you try one of
those: siliconchip.com.au/link/ab5j
Building a sinewave
inverter
I am wondering if you have a design
for a pure sinewave inverter (230V
AC). (A. R., Eltham, Vic)
• We published a 2kW 24V DC to
230V AC pure sinewave inverter in
the October 1992 to February 1993 issues (siliconchip.com.au/Series/173).
That design is outdated, but we have
not updated it, since commercial versions are far cheaper now. There is no
way we could design an inverter for the
cost that you could buy one these days.
Combining AND gates
for a clock
I want to build a clock with local
time, UTC and sidereal time on six
7-segment displays. I would like the
Australia’s electronics magazine
same crystal to run all the clocks. I
have found a circuit to generate the
1.002738Hz for the sidereal clock, and
it also generates a 50Hz for the local
time. But it requires a 1MHz crystal
and a 4068B IC (8-input AND gate).
I found out that the 4060B IC can do
frequency division and could be capable of dividing 2MHz to 1MHz. The
4068B IC is now hard to find (Mouser
has it, but the delivery cost is prohibitive). Can I use seven 2-input AND
gates instead? And how can I divide
the 50Hz signal down to 1Hz for the
local clock? (R. M., Melville, WA)
• Yes, you can make up an 8-input
AND gate from seven cascaded 2-input AND gates. A 50Hz to 1Hz divider
circuit is shown at siliconchip.com.
au/link/ab5i It uses two 4017B ICs fed
with the 50Hz signal from the secondary of a mains transformer, but you
could feed in the 50Hz output from
your digital divider instead.
Looking for historical
documents
I worked at Fairchild Australia in
Melbourne from 1965 to 1974 as an
Applications Engineer and Manufacturing Manager. Recently, I was
asked to contribute to a history of
the manufacture of semiconductors
in Australia.
I remember Jamieson Rowe visited
the Fairchild factory at Kilsyth and
then wrote an article about our factory.
I think Electronics Australia also published articles on other manufacturing
facilities over the years. I would be
very grateful if someone could point
me in the direction of any such articles that I could use.
Do you have a listing of all articles
that I could scan? I am interested in
the period from the 1950s to the 1980s.
(B. O. S., Blackburn, Vic)
• Jim Rowe responds: after a bit of
searching back through old EA indices, I believe I have found that article
to which you are referring. It was in
the February 1973 issue, and titled
“Fairchild now making TO-92 transistors here”. The only other articles on
Australia’s short-lived semiconductor industry I came across were these:
May 1972: “Local Semiconductor
Breakthrough”
June 1972: “Centre Industries
Making GE Diodes”
March 1973: “Philips’ Hendon
facility in SA”
SC
siliconchip.com.au
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