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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
Epoxy for High Power
Ultrasonic Cleaner
I want to build your High Power Ultrasonic Cleaner (September & October
2020; siliconchip.com.au/Series/350),
but I have found multiple J-B Weld
epoxy products and am not sure which
one to use. (M. T., Auckland, NZ)
• We recommend using the original
J-B Weld epoxy. It is sold by Jaycar
(Cat NA1518).
Charging USB host and
OTG devices
Is it possible to power a host USB
device and USB accessory at the same
time? I have found a lot of confusing
and contradictory information concerning this question. There seems to
be a standard, but I am unsure how
the system is actually implemented.
(T. F., via email)
• Perhaps not all devices implement
the standard correctly, but it does support charging both the host and accessory using a “USB Accessory Charger
Adapter”. There is no technical reason
why it should not work. See Wikipedia for more details:
https://w.wiki/t76
https://w.wiki/t77
Updating Colour
Maximite 2 firmware
I have been enjoying MMBasic and
the Colour Maximite 2 (July-August
2020; siliconchip.com.au/Series/348)
for some time now. We are up to CMM2
V5.06.00, and things are looking good.
The problem I have is with loading
new firmware into the Colour Maximite 2 using the USB-A to USB-A cable
in the keyboard port.
I used this method twice successfully with the STM32Cube Programmer software in Windows 7, but now
it will not detect the Maximite any
more. I had to take the case apart and
slide the BOOT switch to SYSTEM and
try again, and now everything is back
to normal – the software detected the
siliconchip.com.au
Maximite, and I could upload the latest firmware.
Is there some way to fix this? I prefer to avoid pulling the case apart
and switching the boot config switch
whenever I need to load new firmware,
even though I don’t have to do that
every day. (R. S., Epping, Vic)
• Geoff Graham responds: There is
no known problem related to loading firmware upgrades on the Colour
Maximite 2.
It sounds as if there is some confusion with the UPDATE FIRMWARE
command. This is equivalent to setting the BOOT CONFIG switch to
“SYSTEM”, but this will only work
when using the alternative method of
loading the firmware via serial transfer over USB.
It will not work when using the
USB-A to USB-A cable in the keyboard
port because you cannot use the keyboard to enter the command in the first
place. When using this method, you
must open the case and set the BOOT
CONFIG switch to “SYSTEM”.
Flashing LEDs on
Ultrasonic Anti-Fouling
We purchased, built and installed
your Ultrasonic Anti-Fouling units
(May & June 2017; siliconchip.com.
au/Series/312) two years ago. Recently, the power LED suddenly stopped
flashing. After two years of fabulous
service, and a lovely clean bottom, we
were taken aback.
We found the 3A fuse had blown
and replaced it. The green power LED
came on, but did not stay on. No fuse
blew, no fault light showed. We then
replaced REG1 (LP2950ACZ) and carefully monitored the slow start-up. The
green power light came on for approximately five seconds, went off, and the
fault LED started a slow flash.
We replaced both 2200µF capacitors, but no joy. Again, the green
power LED lit up, but this time, the
power light went off quickly, and a
few seconds later, the fault LED started flashing.
Australia’s electronics magazine
Many thanks for this brilliant kit,
and any help you can offer to get it back
working. (W. B., Vancouver, Canada)
• You could have a faulty driver
Mosfet (Q1-Q4) or the transformer
windings might have failed (unlikely
but possible). Check the Mosfets for
short circuits between the drain and
source pins (if there is one, you will
get a low ohms reading regardless of
the lead polarity).
If they check out OK, the problem
may be that the soft starting feature
has found fault with the low-ESR bypass capacitors, where there is current
leakage. You could add in a resistor
across the drain and source of Q5 to
counteract the leakage so the circuit
will start up. This can be done on the
underside of the PCB. A 330W 1W resistor should counteract any leakage.
Increasing boost supply
output power
I want to build a switching DC/DC
converter to drive an audio power
output valve from a low-voltage DC
supply. I was thinking about modifying the supply from your Valve Stereo Preamplifier For HiFi Systems
(January 2016; siliconchip.com.au/
Series/295) to do the job. I need about
1-2W continuously at about 250V, and
maybe 3-5W peak.
What changes do I need to make to
your circuit to achieve this?
I checked the data sheet for the
MC34063 switching regulator IC, but
it doesn’t give any details about using
it to drive an external Mosfet as you
have done in your circuit. The data
sheet gives formulas involving the Vsat
value of an external bipolar transistor.
Do I use the Vgs(th) value of the Mosfet instead? (J. H., Glasgow, Scotland)
• First, let’s cover your question about
the Mosfet. When you’re substituting a
Mosfet for a bipolar transistor, replace
Vce(sat) with Rds(on) multiplied by the
expected drain current (Id).
Presuming that Vce(sat) was calculated using the peak current value,
use that same current figure as Id. You
February 2021 107
will need to know the Mosfet’s operating Vgs to determine the correct value
for Rds(on).
As for boosting the output power
of our circuit, we calculate that the
total current drawn by the 12AX7 in
our design is 4mA, so at 250V, that’s
1W. And as described in that article,
the converter is running flat out to
achieve that. Increasing that to 2-3W
is not going to be a simple job, but it’s
probably possible.
Start by reducing the value of the
resistor between pins 6 and 8 of REG2
and loading up the output to see what
it can deliver. We suggest the first test
should be with a 0.1W resistor.
If you can’t increase the output power to your desired level, the next step
is to substitute a larger inductor for
L1. Try a 100µH 3-5A toroidal inductor. You might get better results with
a different inductance value. You can
probably lower the resistor value further with a larger inductor.
You will find it easier to achieve the
desired output power with a higher input voltage, up to the maximum that
the MC34063 and input capacitors can
handle. That limit is 24V with the circuit as presented, or up to 40V if you
increase the capacitor ratings.
NiMH cell recharges
suspiciously fast
Recently, I decided to test several
AA-size NiMH used cells that had been
out of use for several years. It was no
surprise that many were totally flat,
but several showed an open circuit
voltage of 0.6-0.8V.
I have a mains charger with a 25V
AC input that can charge two or four
AA cells. The charger has a red & green
LED indicator that flashes slowly when
the cells are placed in the charger, then
a steady red for about 20 seconds, then
a steady green indication which suggests that the cells are fully charged.
I find it hard to believe that halfflat AA cells can be fully charged in
20 seconds, although I measured their
open-circuit voltage at 1.33V!
Given that I know very little about
the charging characteristics of NiMH
cells, could you refer me to an article
that would answer my query?
What is a safe rate of charge for AA
sized cells? Have you published an
article or a construction kit with instructions to build a reliable charger
with enough capacity to charge up to
108
Silicon Chip
D-size NiMH cells? (R. W., Loxton, SA)
• NiMH cells are typically charged
at a ten-hour rate. So a 1000mAh cell
would be charged over 10 hours at
100mA. Fast chargers require an endof-charge detection method, typically
either using the drop in voltage of a cell
(dV/dt) once charged, or via a rise in
temperature (dT/dt) at the end.
The cell(s) that charged in 20 seconds would have little charge capacity
and are probably high-impedance and
therefore no good. The voltage would
drop as soon as a load is placed on it.
A good cell would not rise to 1.3V so
quickly.
We have published many suitable
chargers over the years, including the
following:
■ SuperCharger for NiCd & NiMH
batteries, November & December 2002
(siliconchip.com.au/Series/111)
■ A Fast Charger For NiMH &
Nicad Batteries, September 2007
(siliconchip.com.au/Article/2337)
■ Float charger for NiMH cells, June
2010 (siliconchip.com.au/Article/180)
■ Burp Charger For NiMH & Nicad
Batteries, March 2014 (siliconchip.
com.au/Article/6730)
■ Intelligent Charger for Nicad &
NiMH Batteries, July 2015 (siliconchip.
com.au/Article/8677)
Repairing speakers
with substitute tweeters
I have a pair of Sansui SP 1000
speakers, rated at 50W/8W. Each has
two 20W 16W tweeters connected in
parallel, and all four are open-circuit.
Trying to source replacement/substitute tweeters is difficult, so would it
be OK to use two 20W 8W tweeters in
series? These speakers are 49 years old
and have some sentimental value. (R.
S., Humpty Doo, NT)
• It is difficult to answer that question without knowing more about the
original tweeters and the replacements, specifically, their respective
sensitivity ratings in dB/W at 1m. You
need those figures, plus the impedance
numbers, to figure out how to correctly
match the new tweeters to the existing speakers.
For example, say that you connect
the two new 8W tweeters in series, then
connect a high-power 16W resistor in
parallel with the pair. That will give
you the same 8W impedance as presented by the original pair, but with
6dB less signal going to the tweeters
Australia’s electronics magazine
(the rest of the power will be dissipated by the resistor).
If the new tweeters are 6dB more
sensitive than the old ones (which
is possible), that would be a good arrangement, giving you a similar balance of high and low frequencies as
before. Otherwise, the result could
sound too bright or too dull.
Your suggested configuration will
probably change the way the crossover
works as the tweeters will have twice
the original source impedance. Without knowing the details of the crossover design, it’s hard to say what effect
that will have.
Regardless of what you end up doing, you might need to make further
changes (eg, adding padding resistors)
to match the tweeter volume to the
other drivers in the system.
Higher power valve
amplifier wanted
I am currently building my second
Currawong valve amplifier (November 2014-January 2015; siliconchip.
com.au/Series/277). In past issues,
you mentioned that you might develop a higher-powered version. Have
you found ways to increase its power beyond 10W/channel? (C. J., Samson, WA)
• The limiting factor in the output
power of the Currawong is the pair of
15W output transformers. The 6L6s
certainly should be capable of considerably more than they are delivering in
this design, although they would likely
need a higher anode voltage.
When we looked at this in the past,
we found that higher wattage output transformers were prohibitively
expensive. The Currawong is costly
enough to build in its current form already, so we didn’t think it was worthwhile to do the engineering work to
design a higher-power version as it
would probably cost over $1000 to
build.
A keen constructor might be able to
figure out how to fit upgraded output
transformers, change the power supply
to deliver higher voltages to the 6L6s
(but not the 12AX7s!) and obtain perhaps 20-30W per channel.
But we just don’t think it’s worthwhile when solid-state amplifiers with
much higher outputs power ratings,
lower distortion, lower noise and with
flatter frequency responses can be built
for significantly less money.
siliconchip.com.au
Building a mains-based
PortaPAL-D with effects
I would like to build your PortaPAL-D portable PA system (December 2013-February 2014; siliconchip.
com.au/Series/177), but I want it to be
powered from the mains, not a battery.
I also want to add the Digital Effects
Processor (October 2014; siliconchip.
com.au/Article/8033).
My question is concerning the power supply. If I install the transformerbased dual rail power supply for the
power amplifier, how can I get the
+12V single rail supply for the Microphone input PCB and the Digital
Effects Processor? I don’t think I can
just step down one side of the dual
rails, as the transformer ground will
be shorted to the signal. What do you
suggest? (V. S., via email)
• That should be possible. The PortaPAL-D is based on the CLASSiC-D amplifier which originally used a mains
power supply (that we published in
December 2012) which produced
±57V and optionally ±15V rails from
an extra set of transformer secondary
windings, or a second lower-voltage
transformer.
Those extra components were not
shown in the article, as the CLASSiCD did not need them, but the PCB has
provision for them. The 7815 on that
board could be changed to a 7812 to
produce a +12V rail.
A separate +12V supply from something like a plugpack or open-frame
switchmode supply could certainly
be used, as long as the two supply
grounds are joined.
Model train controllers
damaged by short circuit
I have purchased a few PWM train
controllers off “fleabay”, but for some
reason that no-one can tell me, I have
lost the ability to control the speed.
They give full power all the time. Do
these controllers “blow up” if a train
derails and causes a short circuit?
Have you designed, or can you point
me in the right direction for a topnotch PWM DC controller? I would
like to use PWM on my two model
train layouts, taking full advantage of
the slow running speed that the usual
transformer won’t allow. Scale speed
is what I am after. I would also like a
forward/off/reverse switch and speed
control potentiometer.
siliconchip.com.au
Others who have tried to help me
suggested adding a self-resetting
thermal cut-out (whatever that is). I
wouldn’t have a clue where to put one,
and I cannot seem to find a 1A version
anyway. (R. L. B., Pine Mountain, Qld)
• It is possible that a short circuit
could have damaged the PWM controllers you bought. You could try connecting a PTC between the controller
and one of the tracks. It would need
to be rated for a trip current slightly
higher than the controller’s rated current. But we aren’t sure that this would
prevent those controllers from being
damaged.
We published the Li’l Pulser
PWM train controller in July 2013
(siliconchip.com.au/Series/178) and a
revision in January 2014. It has short
circuit protection and forward and
reverse as well as speed control. We
think it will do exactly what you want,
and will not be damaged easily.
Ignition system failure
in an older car
I built your High-Energy Ignition
System for Cars (November & December 2012; siliconchip.com.au/
Series/18) from a Jaycar kit (KC5513)
and installed it in a classic club car.
It appeared to be working fine. However, after about ten hours of driving,
the system failed.
I found that REG1 (LM2940CT-5)
had overheated and its ground return track had fused and burnt the
PCB. Also, the label affixed to IC1 had
melted away in its centre. Do I need
to make changes to the circuit for better reliability? (B. C., Dungog, NSW)
• The High Energy Electronic Ignition
Module is generally very reliable. We
think the return current for the coil ran
through the PCB tracks rather than the
connection to the case, due to a poor
ground connection.
Having fixed that, it also wouldn’t
hurt to incorporate the extra protection components that we used in our
Improved Jacob’s Ladder project from
February 2013 (siliconchip.com.au/
Article/2369). It includes extra protection for the regulator, especially where
the coil connection lead is adjacent to
the power supply leads.
Triggering a PIC from a
high voltage source
I am having a most aggravating time
Australia’s electronics magazine
with your High-Energy Ignition System (November & December 2012;
siliconchip.com.au/Series/18). I have
blown up three PIC microcontroller
chips, and cannot understand why. I
am hoping you can help.
I have a dated two-stroke engine
driving a vital piece of agricultural
equipment, and the CDI ignition system has failed with no spark. I am unable to source a replacement part.
I have been trying to manufacture
a replacement ignition system using
your High Energy Electronic Ignition
System project. There is a signal on
the HT lead, around +90V going rapidly to about -90V when unloaded, as
the magnets on the flywheel pass the
poles of the CDI unit. I hoped to use
this as a timed trigger signal.
I have attempted to condition this
signal with increasing severity, but on
each attempt, the PIC microcontroller
input still fails. I currently have a 5V
zener to clamp the voltage at the PIC
pin, with a series resistor, plus capacitors before and after the resistors and
another 27V zener with a series resistor closer to the signal source.
Can you offer any advice or suggestions as to why my attempts to clamp
this signal to 5V have failed? I still
have one unused PIC chip. (D. L., St
Andrews, Vic)
• The unloaded CDI coil might be
producing brief transient high peak
voltage that destroys the PIC input
despite your zener clamps. Zeners
don’t always have a sharp ‘knee’, and
the voltage across them can be significantly higher than expected if enough
current is applied.
Perhaps a better way to protect the
PIC would be to use a transformer
to step down the voltage, such as a
strobe trigger transformer (eg, Jaycar
MM2520) with the secondary connected to the CDI coil, and the primary to the PIC input (via the protection
zeners and shunt capacitors).
That might give you sufficient signal to drive the PIC input. Note that
the CDI coil should be loaded with
some resistance to reduce voltage
transients.
Alternatively, use a 6N138 optocoupler (a 4N28 might be fast enough)
to provide voltage isolation. You
would still need to have sufficient
voltage protection for the LED in the
optocoupler using zeners, a limiting
resistor and a shunt capacitor like in
your circuit.
February 2021 109
CDI wanted for a
two-cylinder engine
I’m looking for a type of capacitordischarge ignition system (CDI) to install on a small two-cylinder engine
that could still retain the original
points. I’m just looking to take the high
power draw off the points.
Would your replacement CDI
Module for Small Petrol Motors
from May 2008 (siliconchip.com.au/
Article/1820) work for this? Do you
have preassembled units or parts kits?
I could not find any of this when I was
directed away from your legacy website. (M. W., via email)
• The May 2008 CDI Module is designed for motors with a trigger coil
and a high-voltage generator coil. If
you have points, then that CDI unit
is not suitable. We don’t sell fullybuilt versions, but we can supply
the PCB – see siliconchip.com.au/
Shop/?article=1820
For points-based ignition systems,
our High-energy Ignition System (November & December 2012; siliconchip.
com.au/Series/18) is suitable, provided there is a 12V supply available.
Soft Starter for
halogen lamp
I have been having trouble with a
bedside lamp fitted with a 28W halogen candle globe. We have a pretty constant 250V here, and this lamp has frequently been blowing globes at switchon. I remember reading quite a while
ago about a soft starter for lamps, so
I searched and found the Soft Starter
listed in April 2012 (siliconchip.com.
au/Article/705).
The article I was thinking of was
much earlier, but I went ahead and
built this project anyway, and it seems
to be working OK.
However, there is no visible difference when first turned on and when
the relay cuts in. It is just as bright as
without the soft starter.
I looked back at the article and realised that it was designed for highcurrent applications, and using it for a
lamp may not be the best choice. The
lamp has a steady current of 125mA
and a cold resistance of 250W. The 10W
thermistor with a current capacity of
15A may not have enough resistance
to limit the current at switch-on.
I thought maybe I should replace the
thermistor with one of about 80W or
110
Silicon Chip
so. This may provide more of an initial voltage drop to protect the lamp.
(B. D., via email)
• You certainly could do that. Try the
MF72-400D9. It is cheap and rated for
mains use. Its maximum steady-state
current is 200mA so should be sufficient, and its cold resistance of 400W
will reduce the initial current by about
two-thirds, giving a much more gradual filament warm-up.
Soft Starter
modifications
In reference to the Soft Starter
from April 2012 (siliconchip.com.au/
Article/705), could I use a more readily available 12V DC coil relay instead
of a 24V type? Obviously, the X2 capacitor and zener would need to be
adjusted, and some resistors to keep
the delay constant.
In terms of decreasing the temperature and/or longevity of the thermistor, to use it with SMPS, LED lighting and computer equipment with
a maximum continuous current of
around 1A, could several thermistors
be put in series (or parallel)? (B. A.,
Dee Why, NSW)
• We did not use a 12V relay because
it doubles the power drawn from the
mains and requires a considerably
larger capacitor. You would have to
increase the X2 capacitor to at least
330nF. If it does not work reliably, try
470nF. As you said, you would also
need to change ZD1 to 12V.
You would also, as stated, need to
roughly halve the value of the resistor
which charges the delay capacitor for
a similar delay to the original design.
You can put several thermistors in
series or parallel, but note that the softstart effect will be stronger if they are
in series and weaker if they are in parallel. If the equipment is only drawing
around 1A, then a series connection is
the best option.
A series/parallel combination of
four thermistors could also be used
and would give the same soft starting
capability but with much less heat per
thermistor. That’s assuming you could
fit them all in the box.
Using the Soft Starter
with a bore pump
I am looking at the Mains Soft Starter
for Power Tools project from July 2012
(siliconchip.com.au/Article/601), and
Australia’s electronics magazine
I am wondering whether it is suitable
for powering a single-phase (capacitor
start) bore water pump of about 1.5kW
nameplate rating.
There is a noticeable torque/kick
that physically moves the pump every time the low-pressure switch needs
to activate – which is many times per
day. I think it would be beneficial for
the general longevity of the motor and
pump components if a soft start controller could be implemented.
Whether this circuit is exclusively
for universal serial wound motors only
hasn’t been conveyed in the original
article, and would guide my attempt
to implement this as a workable solution. (C. T., Sunnybank, Qld)
• It’s possible that the Soft Starter
would help in your case, but we do
not think so. You have three things
working against you trying to use a
simple soft-starting circuit with an
induction motor:
1) You’re reducing the voltage/current but not the supply frequency, so
the motor torque will be very low during the soft-start phase; it probably
won’t be enough to get it spinning,
which means that it will still hard-start
once the relay switches on.
2) The pump is presumably always
primed, so it’s starting under load and
therefore will need to draw a significant current to spin. The Soft Starter
was intended more for use with motors
which start up off-load or have a very
brief initial current draw like most
power tools, or devices with switchmode power supplies.
3) During the initial phase, if the motor doesn’t spin, it’s going to draw a lot
of current and get rather hot (although
the limited soft-start time means that
it’s unlikely to be damaged).
The Soft Starter is not exclusively
for universal motors, but it is far from
ideal for induction motors. It might
work with some small induction motors, such as the shaded-pole motors
often used to drive fans.
Our 2012 1.5kW Induction Motor
Speed Controller (siliconchip.com.au/
Series/25) would do what you want as
it has a soft start feature, but it is much
more complicated and expensive and
only just rated for your application.
Substitute low-noise
PNP input transistors
I am gathering parts to build a stereo
continued on page 112
siliconchip.com.au
Notes & Errata
Busy Loo Indicator, January 2021: at the bottom of the left-hand column on p79,
where the text says the inputs of IC1b are normally high, it should read IC1d instead.
Mini Digital AC Panel Meters, January 2021: if the current transformer secondary
is not terminated with a low impedance, it will generate a very high (and potentially
dangerous) voltage if any significant AC current is flowing in the primary. So make
sure to connect the secondary leads of the CT to the panel meter before any current
is allowed to flow through the primary.
Radiating test antenna for AM Radios, Circuit Notebook, January 2021: the
ferrite rod is 200mm long, not 400mm as stated in the text.
Vintage Battery Radio Li-ion Power Supply, December 2020: on page 28, the
text refers to a 220µF capacitor being charged via a 220W resistor. The capacitor
value is actually 10µF.
Colour Maximite 2, July & August 2020: the SD card socket specified for this
project (Hirose DM1AA-SF-PEJ(21)) is being discontinued by the manufacturer.
Instead, use the DM1AA-SF-PEJ(82) which costs the same and fits the existing
footprint on the PCB.
The March 2021 issue is due on sale in newsagents by Thursday, February
25th. Expect postal delivery of subscription copies in Australia between
February 23rd and March 12th.
Advertising Index
Altronics...............................21-24
Ampec Technologies................. 37
Dave Thompson...................... 111
Digi-Key Electronics.................... 3
Emona Instruments................. IBC
Jaycar............................ IFC,53-60
Keith Rippon Kit Assembly...... 111
LD Electronics......................... 111
LEDsales................................. 111
Microchip Technology............ OBC
Ocean Controls........................... 5
Silicon Chip Binders............... 111
pair of Ultra-LD Mk.3 amplifier modules (March-May 2012; siliconchip.
com.au/Series/27). The transistors
specified for Q1 and Q2, 2SA970 lownoise PNP bipolar transistors (BJTs),
seem to be no longer available.
I am considering using KSA992s
as a substitute. Do you think this will
compromise the performance of the
amplifiers? (I. S., Mitcham, Vic)
• The KSA992 looks OK. It’s hard to
be sure because the way they specify
the noise voltage in the data sheet is
not very useful. We don’t think you
will notice the difference (if any).
We can see some online sellers offering 2SA970s, but we think many
of them are counterfeit parts. Some
people have said that the clone parts
work well, while others say they are
not low-noise types; it probably depends on the luck of the draw. Your
suggestion of using KSA992s is safer
since you can get them from a reputable supplier.
Old remote preamp
not recommended
I was browsing old issues of Silicon Chip and found a project by John
Clarke called the Stereo Preamplifier
with IR Remote Control (September &
November 1993; siliconchip.com.au/
Series/168).
Since then, many newer designs
have been published like the Ultra-LD
Stereo Preamplifier & Input Selector
112
Silicon Chip
that I am happily using together with
the Ultra-LD Mk4 amp. What caught
my attention was the absence of a volume pot and the LED display.
I was wondering if that design is still
valid and if I could build it? I’d need
to find a few replacement components
that’d be obsolete by now. I checked
that I could source the microcontroller online; however, I have no way to
program it. Do you have any advice on
this? (O. A., Singapore)
• That Preamplifier would be extremely difficult to build at this late
date, as many critical parts would be
very difficult to obtain.
The microcontroller would be difficult to program as we don’t have the
facilities for that processor anymore.
We do not recommend that you start
building this project.
Note that we are working on a new
digital preamp design with remote volume, bass and treble controls; however, it is not yet finished, and we don’t
know when it might be published at
this stage.
Problem with 3-channel
Rolling Code Remote
I built this project, described in
your August & September 2009 issues
(siliconchip.com.au/Series/39) from a
Jaycar kit, Cat KC5483. All functions
are operational, but the range is only
about 3m.
I have checked the antennas on both
Australia’s electronics magazine
SC Micromite BackPack............ 96
Silicon Chip PDFs on USB....... 87
Silicon Chip Shop.................... 97
The Loudspeaker Kit.com........... 7
Tronixlabs................................ 111
Vintage Radio Repairs............ 111
Wagner Electronics................... 51
the transmitter and receiver but cannot
find a fault in the construction. Do you
have any suggestions? (G. P., via email)
• The most likely cause is the soldering to the coiled wire antenna. The
wire is enamel-coated, and unless
this is scraped off well before soldering, it may not form a good connection, reducing the effectiveness of the
antenna.
You probably have already checked
these connections. However, a multimeter measurement of resistance from
the antenna input on the receiver module (or output for the transmitter module) to the free end of the antenna will
verify if this is a low-ohms connection, as expected, or high-resistance/
open-circuit.
Another thing to check is that there
is the full 5V DC supply to the transmitter and receiver modules and that
the transmitter supply stays at 5V
when transmitting.
SC
siliconchip.com.au
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