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. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097; or
send us an email.
High energy ignition for a Citroen 2CV
I built the High Energy Ignition system from the June 1998
issue and successfully installed it in my Citroen 2CV (2-cylinder 600cc air-cooled engine) using its original contact points for triggering. It worked first time and worked well for about two weeks, starting first time, every time and running very well with noticeably better acceleration.
Then I noticed that its performance degraded rapidly over a
period of a week or so. It would tend to stall at traffic lights and would be difficult to start, with the engine missing a beat. As I use the car daily, I switched the car circuit back to its normal direct point switching.
Would you know what is wrong with the circuit? Is the output
transistor at fault?
St Marys, SA).
We suspect that the problem is that the points are oiling up from fumes in the engine. Periodic cleaning of the points will help but you may need to increase the points wetting current by using a second 5W resistor in parallel with the original.
Li'L Snooper camera switcher
I am interested in building your Li'L Snooper camera switcher
from the June 2001 issue. Will this circuit be suitable for colour cameras; one
is CCD, the other is CMOS? If not, can you recommend any mods to make it
Snooper will work with any camera that puts out a 1V composite video signal.
Volume control for amplifier module
I recently bought a 50W stereo amplifier module kit from
Altronics. It was published in the February 1995 issue of SILICON CHIP. I have reviewed the
design and the only thing that I could think of putting in the circuit was a
volume control. How do I do that?
answer is quite simple, use a 10kΩ dual gang logarithmic pot. The pot wiper goes to the
amplifier module in each channel.
Raucous alarm not loud enough
I have just built the "Raucous Alarm" from the January 2002
issue and it works just fine. Is there a simple, easy way to increase the output
to say 110dB or thereabouts, as I would like to use it in a large hall, full of
answer is to use the most efficient piezoelectric tweeter you can buy and use a
15V supply. We suggest the CTS KSN 1177A from Altronics (Cat C-6170). It has an
SPL rating of 99dB at 2.83V/1m.
Noisy transformer in battery charger
I recently purchased the Multi-Purpose Fast Battery Charger
MkII from Jaycar Electronics (featured in the June & July 2001 issues) and I
am getting serious buzz or hum from the inductor. The severity of noise depends
on the battery being charged. A single NiMH cell makes more noise than a pack of
4 or 8. I wound the inductor with even pressure but the windings are not
settling. Is this cause for concern? Would dipping the inductor in epoxy or
"Liquid Tape" assist in the reduction of high frequency noise? Or do I need to
wind the inductor again?
I was curious about the gap in the ferrite core and do not
understand the concept behind this, especially since the centre core (E core)
has an air gap. Does this need a spacer as well?
Also, when the batteries are discharged I am surprised to find
that a (cycled) 4.8V 1500mAh NiMH pack lasts only 2-3 minutes. With the constant
discharge of 2A (Refresh Rate) shouldn't they last longer? Around 30-45 minutes?
Noise from the transformer is not a cause for concern, apart from the
irritation, of course! Usually it is caused by the ends of the core pieces
vibrating against each other and the surrounding former (magneto-striction) or
is caused by loose turns in the windings. The solution is often to glue the two
halves together or, as you suggest, to impregnate the core with varnish. You
could also dip it in thin epoxy but make sure it is thin, as heat must be able
to escape from the core and windings.
The gap between the core's centre legs is created to prevent
the core from saturating at high power levels. When the core of an inductor
saturates, it acts more like a resistor than an inductor, with current flow
through it limited only by the resistance of the windings. When that happens,
power dissipation is usually very high and efficiency drops.
The size of the gap is very important and is calculated
according to core characteristics and peak current - be sure to follow the
construction details exactly.
In our opinion, the Multipurpose Fast Charger Mk II is not
suitable for charging small cells, and in particular NiMH-chemistry types.
Manufacturers recommend that small NiMH cells (AA, AAA, etc) should NOT be
fast-charged at greater than 1C, which equates to 1.5A for your particular
Having said that, you will probably be able to successfully
charge a NiCd pack this small using the temperature sensing option, but make
sure that the thermistor is in close contact with the pack (or one of the
The ideal answer though is the SuperCharger design featured
elsewhere in this issue.
Full range equaliser
I was hoping you may be of assistance with a project featured
in the July 1996 issue, namely a Parametric Equaliser. What modifications would
need to be made to make each band full range instead of the three separate bands
(low, mid & high)?
Although we have not tested this idea, the circuit could be made
adjustable over the entire audio spectrum if the capacitor and resistor values
are used for the treble section but with the frequency adjust potentiometer
(VR9a and VR9b) changed from 25kΩ to 200kΩ. The change in frequency with respect to pot movement would
be rather coarse, however.
Video enhancer adds noise
I have purchased Jaycar's AR-1820 Video Enhancer. I realise
it's a simple device but I'm wondering if you have any further user tips for
For example, I notice that when applying the "Sharpen" function
to a DVD dub, ghosting occurs. I find that DVD dubs are best without this
function enabled. Is this correct?
of the sharpen function will tend to emphasise any noise in the video signal so
ghosting is also a possibility. With a DVD the signal should optimum anyway, so
don't use the sharpen function.
Needs 12AX7 preamplifier kit
I've been searching in vain for a simple kit to plug my bass
guitar into. I currently run it into a 4-channel mixer, then to a 50W
(February 1995). Anyway, the bass misses the "valve sound" and I was wondering
if you have a kit, or know of a kit that is a basic mono preamp, with something
like a single 12AX7?
"Electronics Australia" described guitar amplifiers with a 12AX7 input in
October 1962 and in June 1967. They are quite different. We can supply
photocopies of the articles for $8.80 including postage.
Universal stereo preamp level control
I have purchased and built a Universal Stereo Preamplifier from
Jaycar Electronics (SILICON CHIP, April 1994). I have built it as a phono configuration to connect to a
computer sound card for recording LPs. The unit seems to work well, however I
found that the output level is a little high causing a small amount but annoying
As I am new to electronics, I would like to know if it's
possible to change the value of one or some of the components to reduce the
output level or better still put in a potentiometer or similar.
output from the preamplifier can be attenuated using a logarithmic
potentiometer. Connect the preamplifier output to one side of the potentiometer.
The other side of the potentiometer connects to the ground while the wiper or
centre connection connects to the PC's sound card input. The potentiometer
should increase the level of signal when wound clockwise and decrease the level
when wound anticlockwise. A 10kΩ value would be suitable.
If the pot works the other way around, with decreasing signal
when turned clockwise, reverse the outside connections. A dual-ganged pot would
be more suitable as it can adjust both left and right channels
Tape cassette record circuit
I was wondering if you have a circuit, PC board layout and
construction method for a cassette tape record/playback device, with AC bias. I
need to construct about 20 of these units for a 4-track tape loop machine I have
built. I have the mechanics done and now need to put in the electronics.
Because I need so many circuits ( 5 heads, 4 tracks = 20
circuits), I did not want to try wrecking old cassettes, as it would get too
messy to put it all together. Ideally, I would like a circuit which uses the
same head for record and playback, so I can record and playback using any of the
"Electronics Australia" described a stereo cassette deck in August &
October 1974 which had AC bias. We can supply these articles for $8.80 each
Jammed slugs must be fixed
I have been given the task to assemble the MiniMitter kit
featured in the April 2001 issue. I have completed the assembly of the kit,
including changing the mike plug to an RCA type. On test, the output was very
low and unstable. I have installed new batteries.
Being an amateur radio operator, I found this kit good to
assemble but found the slugs jammed in the coil formers; once they were screwed
in, that's were they stayed. What next?
Medlands Beach, NZ).
jammed slugs in the formers must be fixed as they are the means to aligning the
transmitter to a particular frequency. If you need to purchase new slugs, use
Use an aligning tool to adjust the slugs to prevent them
cracking. Adjust both cores carefully to obtain the correct tuning in stereo for
the particular station frequency you are receiving on.
What is a dummy battery?
Call me a dummy if you like but the Circuit Notebook item in
the December 2001 has caused confusion. It was for measuring current of a DC-DC
converter. Now I've used dummy loads but what is exactly a dummy battery. Please
explain in more detail please.
South Morang, Vic).
expression "dummy battery" is explained in the fourth paragraph of the article
on this circuit. As it says, the dummy battery replaces all the cells in the
device under test and a variable voltage supply provides the power for the
device. In the simplest application, the dummy battery could be a 9V battery
Sound meter wanted for PA installations
You may care to consider doing a project which is able to
measure in a dynamic fashion the sound level in a PA installation. I help out at
our local church with operating their PA system and with the varied number of
people using the PA system, it can become awkward to ensure that the level of
sound heard by the audience is constant.
In most fixed PA installations, unless the controller is
located within the listening area, it can become tedious and inconvenient to
have others relay messages to the controller on whether the volume levels are
set correctly. Even if you can see the audience and the speaker, often the sound
heard by the operator is different since he is a little remote from the
What would be useful is a sound level meter which could be
mounted in the control room with a microphone located in the listening area. The
meter could be switchable between RMS and peak levels to determine the optimum
While there are a number of sound level units available from
many electronics outlets, these are typically portable units which require the
operator to be in the listening area and do not generally lend themselves to
being run remotely. In any event, the displays are typically quite small.
What would be more useful is a jumbo size display comprising
LEDs which could be mounted on a wall in the control room to allow easy viewing
by the operator.
may want to consider our Sound Level Meter Adaptor for DMMs published in the
December 1996 issue. You could install several of these around the auditorium
and then switch the DC output signals to a DMM with large display at the control
desk. We can supply the December 1996 issue for $7.70 including postage.
Digital thermostat needed for a PC
I am currently studying electronics at school for my Tasmanian
Certificate of Education. One of the assessment things I need to do is a project
by the end of the year. I have been looking into building a digital thermostat
to be placed inside the PC case. I would like this to control a fan so if the
temperature exceeds a particular level, the fan switches on. I would also like
it to run off the PC power supply.
We published a
thermostat fan control as part of a speaker protection circuit for the Ultra-LD
amplifier, in the August 2000 issue. You could just build that part of the
Checking Dr Video for damage
I recently assembled a Dr Video kit, as published in the April
2001 issue. Upon running power through it I found I had made a couple of errors.
Could you please advise me whether this may have damaged some of the
My first problem was that I accidentally bridged solder across
two of the terminals on IC2. Looking at the PC board overlay, the bridge
occurred between the lower 5th terminal and the solder imprint running to the
terminal on the opposite side.
The other problem was that I inserted three of the chips upside
down. This was because I determined their direction by following the lettering
as in the circuit diagram, as opposed to paying attention to the direction of
the cutout markers. Having discovered and rectified these faults, the unit is
working after a fashion.
There is a television picture when the unit is on and no
picture when the power is turned off. The problem is that white horizontal lines
flow down the picture and make it unwatchable. This occurs both when the sharpen
button is depressed and when it is not. Is this horizontal jitter that may be
rectified as per your instructions or am I likely to have some other problems?
Have you replaced
the chips which were inserted wrongly and have you checked the voltages,
particularly the -5V rail. It is highly likely that IC4 was damaged and we would
be surprised if IC1 and IC7 were not also damaged. IC2 is unlikely to have been
Interference problem with volume control
I have built the Remote Volume Control featured in the June
2002 issue of SILICON CHIP but
it has a bug. At switch-on, (after initial checks) the ACK LED is permanently on
- flashing only when a remote button is pushed. Also when Mute is pushed, the
pot doesn't rotate the full distance, regardless of where VR1 is positioned.
I've replaced all the transistors but since then the mute
hardly works at all. I did notice that when placing a finger near or on the
terminals of the 100μF capacitor on terminal 3 of IRD1, the ACK LED seemed to behave properly.
Replacing the capacitor did not rectify the problem. I suspect IRD1 but would
like your thoughts first.
I only tacked IRD1 in by the tips of the leads (for testing
purposes) so I doubt that it's heat damage. Also IC1 and IC2 are in sockets,
inserted with a proper insertion tool to prevent static damage, so they should
be OK. Could IRD1 be static-damaged or crook from day one?
sounds like IRD1 is playing up. It probably is not faulty but is picking up
electromagnetic interference or even infrared interference, causing it to
receive and deliver a signal all the time.
To solve this, try using a larger capacitor (than the 100μF) across the supply to IRD1
- 470μF may be
sufficient. Also IRD1 may need shielding. Try covering it with a metal shield,
using aluminium or tinplate (cut from tin can). The metal shield needs to be
earthed to the 0V supply of the IRD1. Also a hole is required for the
Calibrating the Lil Powerhouse supply
I've built the Li'l Powerhouse kit from the June & July
2000 issues and I am having some problems with it.
First, the maximum output voltage is only 38V not 40V. I cannot
calibrate the panel meter to the voltage; ie, I calibrate it to 0V but when I
increase the voltage, the panel meter doesn't match what the DMM reports. I'd be
grateful for any tips.
answers to your questions are as follows:
(1) The lower output voltage is probably due to either a low
mains supply or a transformer that has a little less output than the unit we
used in our prototype.
(2) You don't mention the actual difference between your
multimeter and the panel meter. A small difference is OK, as the panel meter
(and perhaps your multimeter) are not precision devices.
However, if the difference is large, then it is almost
certainly due to either: (a) incorrect full-scale calibration of the panel
meter; or (b) a problem with the +5V or -5V rails.
When performing the voltage calibration, be sure to follow
these steps exactly (there should be no load connected to the output
(1) Disconnect the wire from the pole of S4b. This ensures that
the non-inverting input of IC4 (pin 3) is at 0V. Adjust VR5 for a reading of 000
on the panel meter.
(2) Reconnect the wire to the pole of S4b. Set the meter switch
(S3) to the "Volts" position and connect your DMM to the output terminals. Set
the load switch (S2) on and using the "Voltage Adjust" pot (VR1), adjust the
output voltage to get 37.00V on your DMM.
(3) Now connect your DMM between pin 6 of IC4 (marked TP1 on
Fig.6 of the overlay diagram) and 0V (marked GND) and set it to read millivolts.
Adjust VR4 for a reading of 370mV on your DMM.
(4) The panel meter should read 37.0V. If it does not, then
adjust the trimpot built in to the panel meter (accessible through a small hole
at the rear) to get the correct reading.
By the way, you should refer to Notes and Errata from the August 2001 issue
for additional information about calibrating the current reading.
Better reception from two antennas?
I have a 4X4 and travel to many places in the Outback. I like
to listen to the car radio and have noticed that with an aerial mounted on the
right rear quarter of the vehicle, the radio has a much better reception if the
left front of the vehicle is aimed at the transmitter. This presents a problem
because roads are not always correctly orientated.
Is it possible to use two antennas and couple them via matching
stubs of coax or a resistor network? The plan is to use two equal antennas,
vertical, on the mudguards, just forward of the windscreen to get a more
circular reception pattern. Do you know of the correct way to couple antennas to
work on both FM and AM?
is theoretically true that two antennas can be connected together with a
suitable phasing system to improve reception - for example, phased TV antennas
are often used in low signal areas. And for years, truckies have used twin CB
antennas mounted on their mirrors, again connected via a phasing
However, because of the differences in mounting positions and vehicle types,
it is rather difficult to forecast the directional pattern you will achieve
using two antennas. The best receiving antenna (as far as uniformity of
direction is concerned) would be mounted right in the middle of the vehicle
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.
Advertisers are warned that they are responsible for the content of all
advertisements and that they must conform to the Trade Practices Act 1974 or as
subsequently amended and to any governmental regulations which are