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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 an email to

Do battery reconditioners work?

I saw an advert in a 4WD magazine for a car battery reconditioner which brings batteries back to life. It goes in line with the battery and charges it, restoring the battery. What do you think about it? (L. S., via email).

  • There may well be some truth in this product and it may be along the same lines as the battery desulphator circuit we published in the Circuit Notebook pages in February 2003. Note that we have yet to try such a circuit.
  • NTSC version of TV Pattern Generator

    I am purchasing two Programmable TV Pattern Generator kits (SILICON CHIP, June & July 1997) from the local Altronics store. I wish to adapt the design to provide RGB & sync outputs (I presume I can use the signals applied to the AD722) and also wish to have an NTSC video signal option. I only have data for the AD723/724/725 devices so in regard to the AD722, can I simply change crystals to achieve this? (W. A., via email).

  • Pin 11 selects the NTSC or PAL operation. Set pin 11 high for NTSC. Also change the crystal to 14.318180MHz.
  • Replacement for Hall Effect sensor

    Could you tell where can I get the HKZ101 and MJH10012 required to build the High Energy Ignition – I don’t want to buy the kit, I have been offered alternatives, UGN3503U and MJ10012 respectively. Are they compatible?

    Finally, how do you connect the Programmable Ignition Timing module to the Multi-Spark CDI?(D. S., Bandung, Indonesia).

  • The HKZ101 is obsolete and no longer available. Unfortunately, the UGN3503 is not the same and is unsuitable.

    You can use the Honeywell 4AV16F Hall Effect Vane sensor but note that a rotating soft iron vane is also required to pass through this sensor. The Hall sensor is available from Farnell Electronics –

    The MJH10012 is available from Jaycar – contact

    Interfacing the Programmable Ignition to the Capacitor Discharge Ignition requires two connections as follows: (1) connect the output of the trigger circuit to the points input of the Programmable Ignition; and (2) connect the Programmable Ignition output to the main circuit at the point marked "To Trigger Circuit"; ie, to the 10kΩ base resistor for Q4.

  • Using the Remote Extender with Foxtel

    I purchased one of your Remote Control Extenders (from SILICON CHIP, July 1996) and have been very happy with it. However, I recently changed to a Foxtel Digital box and the Remote Extender will not work with this unit. I have tried adjusting the carrier oscillator with no success.

    Can you tell me what to do next? (P. W., via email).

  • We’re not aware of the infrared protocol or carrier frequency used by the Foxtel infrared remotes so cannot be certain why the Extender is not working. However, some constructors have been able to get their kits working by subsituting a different IR receiver module (eg, Altronics Z 1611).

    These is also another possible solution. A learning remote could be used to store the recalcitrant remote codes and this then used with the Remote Extender. Give it a try.

  • Studio 350 amplifier for a car

    I am considering starting work on the Studio 350 power amplifier module (SILICON CHIP, January & February 2004) but would like to adapt it for use in a car. I’m sure I could use a power inverter for this but would rather do it as part of the amplifier itself. How would I go about doing this? Is it possible? (D. T., via email).

  • You need a massive inverter to run the Studio 350 power amplifier – about 600W.

    It just so happens that we described a 600W DC-DC inverter in the October & November 1996 issues. However, it would be expensive to build and it would be far more practical and cheaper to buy a ready-made car amplifier. We would love you to build the two kits but the expense would be high.

  • Midrange boost for guitar

    I have a Champ audio amplifier kit (SILICON CHIP, February 1994) that I’d like to use in my guitar as an onboard mid boost. What modifications would you suggest I make to it? (B. D., via email).

  • The Champ is not really suitable for guitar mid boost. It does not have a high input impedance or any mid-range band-pass filtering.

    The DI Box published in the August 2001 issue would be more useful. It has a 3-band equaliser and so the midrange can be boosted.

  • Master preamplifier connection

    I’d like to connect four power amplifiers to one master preamplifier. What precautions should I take in terms of the reduced impedance load of the power amplifiers as seen by the preamp?(P. S., via email).

  • It largely depends on the input impedance of the power amplifiers and to a lesser extent, on the minimum load impedance that the preamp can drive. In general though, if the combined input load of the power amplifiers is more than say, 10k, then there should not be any problems.
  • If it is less, you might consider providing a buffer for the preamplifier, along the lines of the audio stage in the Video/Audio Distribution Amplifier featured in the November 2001 issue. Note: if you do use this buffer (based on an LM833), the individual 47kΩ output resistors should each be changed to 1kΩ.

    Speed Control kit for RC boat

    I have purchased a 10A DC Speed Control which was published in the June 1997 issue. I’m wanting to connect a receiver to it for use on an RC boat. I was wondering if you could point me in the right direction for a guide on how to achieve this. (N. R., via email).

  • The 10A circuit is not suitable for radio control. Have a look at the 50A speed controller in the May 2000 issue. It is designed to work in an RC system.
  • Level meter for digital camera

    I want to monitor an analog audio signal (something like a VU meter) as it passes through a microphone and into a digital camera; preferably something mobile that’s easy to move around with. I wonder if the Loudspeaker Level Meter featured in the April 2004 issue would be appropriate. (P. M., via email).

  • You can use the Level Meter but the gain of IC1 may need adjusting. IC3 would be best replaced with a log version (LM3915; Dick Smith Cat Z-6297). The scale on the display will then be 3dB per LED.
  • Intercom for aircraft wanted

    Do you have any duplex intercom kits? This is for an aircraft application. I want to be able to talk to other passengers as well as hear myself while we are wearing our headsets. Do you have anything suitable? (A. M., via email).

  • Have a look at the Multi-Station Headset Intercom from the June & July 1992 issues.
  • Connecting a VCR to a PC

    My son was given a Panasonic NV-SJ400 VCR in excellent condition. Unfortunately, we do not have the instruction manual and we cannot find the channel that will let it speak to the computer so we can set it up. Can you help? (B. K., via email).

  • All you have to do is connect the A/V output from your VCR to the VIVO (video-in/video-out) socket on your PC’s video card. There is no need to know the RF channel of the VCR’s modulator. If your video card doesn’t have a VIVO socket (and a lot don’t), then you will either have to replace it or purchase a separate video capture card.
  • Roof blower control wanted

    I am looking for a circuit which is used to activate a blower to blow hot air from the roof space into several rooms if the temperature in the roof space is higher than the temperature in the room or rooms and only if a master switch is activated for the heating action.

    A similar circuit may have been described which switches on a pump to circulate water from the solar panels to a tank below only when the temperature in the panels is higher than the temperature in the tank. (D. W., via email).

  • We published a circuit to do this in the Circuit Notebook section of the March 2002 issue of SILICON CHIP. It comprised two temperature sensors (LM335Z) and an LM393 comparator. This drove a Mosfet to power a pump motor for a solar hot water system. It could equally be used for an air pump fan in the roof cavity. The master switch you require can either switch power on and off for the circuit or for the fan motor directly.

    Note that an air filter system would be required to remove dust and fibre glass (when insulation is used in the roof space) from the roof cavity.

  • Higher power for bridged modules

    Since the upgrade model of the ETI-480 amplifier can only drive 8-ohm loads under bridging, I was wondering if it was possible to add another push-pull output transistor pair to increase the power output of these modules or are there other limiting components, or will it mess up the biasing? (R. G., via email).

  • We assume you are referring to the SC480 presented in January & February 2003. If so, it is possible to add parallel output transistors to increase the current capability of the output stages (for two modules) but the whole project becomes uneconomic and very bulky. You would be better off going for a higher-rated module such as the Plastic Power amplifier described in April 1996. It can deliver 175 watts RMS into a 4-ohm loads and up to 230 watts music power, and at lower distortion.
  • Jacobs Ladder to drive spark plugs

    I am looking for a kit for an automotive project that I am building. The requirement is to continually ignite from one to four spark plugs at the flick of a switch. I was going to use the Jacobs Ladder kit (SILICON CHIP, September 1995) but I’m not sure it would work if I replaced the wires with spark plug leads and added spark plugs to the end of them. What do you think? (F. S., via email).

  • You should be able to use the Jacobs Ladder circuit to drive the spark plugs without problems.
  • Repairing a talking radio

    I have a talking clock radio that I am quite attached to. Unfortunately, when I recently dismantled it to clean the switch contacts, the LCD screen removed itself from the circuit board and the attaching strip. Being attached by this rubber strip with micro conductors has caused me great distress considering how I will repair the connection.

    Is my only solution to get out the microscope and some conductive epoxy glue and try and repair it? Or am I able to purchase a replacement LCD mounted on a board that I can solder?(D. V., Newcastle, NSW).

  • Just reassemble the unit so that the LCD is sandwiched against the elastomeric conductor strips on the PC board. It should work.
  • Correct connection for HEI system

    I have just assembled the High Energy Ignition system and installed it on the car. There is a problem that I do not know how to solve and where to start. I built the kit from the diagram for ignition with points and although the car won’t run, the problem seems to be at the distributor. I have power to the HEI and power at the negative side of the coil.

    I connected a plug lead to an external spark plug and cranked the engine over. The plug fired only once. I put a test lamp on the wire to the distributor from the HEI and there is power there the moment the starter is tuned on, then nothing. Any ideas on what to look for? (R. M., via email).

  • Power for the High Energy Ignition system must be obtained from a switched 12V supply via the fuse box. This connection must apply 12V when ever the ignition is on and not only when the starter motor is running.

    Also note that only one points input is normally required. Remove the diode associated with the points input that is not used.

  • Programming PICAXE via USB

    I was wondering if it is possible to program PICAXEs using a USB-serial converter module from DLP design, based on the FTDI FT232BM IC. The device only has 5V logic levels on the serial lines – not true RS232. Do I need to modify the programming circuit or change the two resistor values? (L. W., via email).

  • The PICAXE programming system will work with certain types of USB-to-serial port adapters. Go to and search for "USB" to find out more.
  • Circuit for the Cylon Voice

    I am after an old kit from "Electronics Australia" or ETI which was called the "Cylon Voice". I am not sure whether it used a XR2206 IC or not and if the IC it used is still available.(R. M., via email).

  • The Cylon Voice was described in the January 1981 issue of "Electronics Australia" and did use an XR2206 which was rather heavy on batteries. We don’t know of a current source for the XR2206.
  • We published an equivalent circuit, the Vader Voice, in the September 1995 issue of SILICON CHIP. Its current consumption was much less than the Cylon Voice.

    Subwoofer controller times out

    I have built one of the subwoofer controllers (SILICON CHIP, December 1995) and all is working OK except it has problems with low signal levels; the timer times out whilst in use. I was wondering if it would be possible to adjust the sensitivity of the VOX circuit to cope with lower levels of input to the controller to enable switching. High efficiency speakers are being used and the unit is OK just above normal listening levels.

    I use the 15W Class-A circuit (SILICON CHIP, July & August 1998) and it is very sweet indeed. Any chance of a 30 watter in the future? (W. C., via email).

  • To reduce the incidence of dropout try increasing the value of R40 to 330kΩ. This reduces the feedback around IC2b.

    We may do another class-A amplifier but it would have to be more than 30W to make it a worthwhile increase over the 15 watter.

  • Backup for cordless phones

    Some years ago you described a construction article on a gel-cell backup for telephones. Can you please tell me the project/kit number, board number and if any of the kitset suppliers produced same? (E. R., Cobram, Vic).

  • The project was entitled "Backup Battery for Cordless Phones" in October 1999. The PC board number was 12510991. It was intended to provide backup power for the phone/base station of a cordless phone system. A kit was produced at the time but it is no longer available.
  • Preamplifier for projector photocell pickup

    I am currently updating a pair of RCA 1018-F 35mm film sound heads. I think they were made around the 1935 mark. They are in good condition but need to be converted to SVA (Stereo Variable Area) pickup. This involves removing the old photocell and replacing it with a split solar cell, one side per soundtrack half.

    As I have very little money to spend on the project, I cannot afford to buy a commercial split cell so I improvised by purchasing a "hobby cell" from Dick Smith and modified that. Bingo! Instant stereo cells.

    My question refers to the preamp I am using to interface the cells and power amplifier. I have built the "Universal Stereo Preamplifier" published in SILICON CHIP in April 1994 and am very happy with the performance of the unit but I need advice on a design modification.

    Testing with the projector running and the solar cell installed exhibit an "RIAA-like" frequency response, ie, bass boost and treble cut. What components should I change, and which values, in order to flatten the response of the design? If possible, some treble boost with a flat bass response will be the ideal as cutting treble is simply a matter of de-
    focussing the sound lens; otherwise a flat response is perfectly OK. The version of the preamp I built is the microphone version. Should I have built the "Tape" version instead? (I. P, Imbil, Qld.)

  • The preamplifier you’ve built is not suitable as it stands – you do need treble boost, etc. The best way to work out what you need would be to have a look at the Optical/Magnetic Preamp for projectors, produced by Jim Rowe way back in October 1975 in "Electronics Australia" magazine. You can then modify your existing preamp to do the same function

  • Weather satellite receiver is noisy

    My son-in-law, a medical electronics technician, has made a good job of Weather Satellite receiver (SILICON CHIP, December 2003) and it seems to be properly tuned according to the instructions, yet its performance is very poor. No satisfactory pictures have been received.

    Compared with an old kit receiver, sold by SciSat products in Queensland about eight years ago, the new unit is much noisier. With the same antenna and masthead preamp used on both receivers, the Sci Sat receiver gives good pictures, while the new kit either fails to lock on or produces a screen full of snow with no picture detail.

    Could you please help?(T. B., via email).

  • It sounds as if either your IF chip or RF stage is "taking off". Have you checked the RSSI voltage (across the 390kΩ resistor), when the RF control is turned fully anticlockwise? It should be below 0.27V if the IF chip isn’t oscillating.

    Turning up the RF control shouldn’t make the voltage rise much, if there’s no signal input to the receiver. If it does, the RF stage may be oscillating.

    A small number of these receivers have needed a small earthed shield plate over the top of the IF chip, to keep it from taking off. Similarly one or two have needed additional bypass capacitors from the source of the RF amplifier to ground, to keep it stable. We suggest 47nF SMD capacitors for this if they’re needed, as these have extremely low self-inductance.

  • Radon detector wanted

    With the ever-increasing growth of dense city housing, the design of houses is becoming more and more restrictive to the flow of air through the buildings.

    Radon is a documented (second highest) cause of adeno-carcinoma of the lung in non-smokers and smokers (cigarettes) alike. It would be very useful to be able to detect the radon levels in the household via continuous monitoring.

    I have seen some Electronic Radon Detectors on the market. An example of an EPA (US) approved model is:

    There are no products available in Australia that cater for the home/office environment. I am proposing that your gifted technical staff design a homemade kit using a radon detecting transducer. Is this feasible? (G. S., via email)

  • While a solid state alpha scintillation counter is relatively easy to design, it does not necessarily give an indication of radon or its daughter elements with their short half lives.

    We think that if you are concerned about a possible build-up of radon in your house, you should consider installing an under-floor fan. If the underside of your house is well-ventilated, or it is built on a concrete slab, it is highly unlikely that there is any problem with radon build-up. It is mainly a problem in cold countries where houses are well-sealed against air leakage.


    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 applicable.

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