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24V versions of LED modules wanted

Why is it that the LED lamp modules for cars, featured in the March 2003 issue, are only for 12V systems! Many of my mates read SILICON CHIP and drive different makes of trucks and have asked me if they these modules could be used in a 24V system. So would you consider publishing the 24V component list for these modules?

(C.S., via email).

Unfortunately, it is not a simple matter to produce 24V versions of the various LED lamps. That's because increasing the values of the current limiting resistors means than power dissipation becomes excessive in the limited space available.

A better solution would be to have longer series LED strings to run from the higher voltage but that is not easily done with any of the existing PC boards.

No sparks on Jacob's Ladder

I recently purchased the "Jacobs Ladder" kit (SILICON CHIP, September 1995) from a local Jaycar store.

I have come across a slight problem. Everything is as it should be but when connected to a brand new 12V car battery, there are no sparks sent up the ladder itself. I have checked it over more than once. So what do I do now?

(C. W., via email).

You will have to do some troubleshooting. For example, is there a low voltage at the collector of Q2? If so, try shorting its base to the emitter. This should give a single spark.

If that happens, you have a fault in IC1 or Q1. You will need to do this process of elimination to find the fault. Also, use your multimeter (Ohms) to check that the ignition coil is OK.

No quiescent current in amplifier

I am building the SC480 amplifier at the moment. I have done all the tests, bar one, where you must wind trimpot VR1 to make the resistors have 28V across them. However, VR1 has no effect whatsoever. Any ideas?

(P. Z., via email).

It sounds as though you might have a short in the Vbe multiplier circuit involving Q7. Either the transistor itself is short circuit between collector and emitter or there is a solder splash on the board shorting the collector to base (turning the transistor fully on) or between collector and emitter.

Another possibility is that you have an open circuit in the connection between base, the 100W resistor and VR1. Again, this will turn the transistor (Q7) fully on and there will be no adjustment possible; ie, zero quiescent current.

Servo control with a potentiometer

I am looking for a circuit or design that can smoothly control a servo motor (as used in R/C cars) by using a potentiometer. Would the circuit in the May 1994 issue cover this?

(S. S., Brisbane, Qld).

The May 1994 circuit will do it or you can look at the Jumbo servo in the May 2001 issue. There is also a dual servo control for panning a video camera in the January 1998 issue.

Dancing waters display

I am attempting to make a "Dancing Waters" project. I saw this in America a long time ago (40 years). It consisted of jets of water which oscillate in tune with music played in the control box.

My memory of the details are hazy but I imagine the jets rose higher as the music note became higher and more water flowed when the music was louder. A friend suggested that a Musicolour ("Electronics Australia", September 1976) could serve this purpose.

I intend to control the oscillation of the jets with a variable speed motor, preferably at low voltage. A system of coloured lights on the PC board would be an advantage.

Basically, I need a PC board which will "read" the frequency and voltage of the current going to the speaker and convert it to current to operate motors and solenoids. Are you able to supply such a PC board and wiring diagram?

(T. G., via email).

Have a look at the 12V LightShow published in the January 1998 issue. It works from 12V AC or DC and is intended to drive halogen lamps but it could also drive 12V motors or solenoids provided they have reverse biased power diodes connected across them.

Converting phono inputs to line inputs

Like thousands of others, I've recently got a DVD player and I am currently playing DVD sound, CDs and MP3s through an old but good Leak stereo amplifier. The sound is really good but I would like to play it through my late model stereo system to allow selection and volume/mute control from the remote and get rid of the additional speakers.

The problem is, the only unused input available on my late model Sharp stereo system is the phono input which is not compatible with the DVD output, I think this is because the low level signal from the pick-up is preamplified before going into the main amplifier and now the DVD output overdrives it.

Is there a simple way to overcome this with a commercially available product or has SILICON CHIP had a kit which would do the job? I realise this won't give me "5.1 Home Theatre" sound which the DVD is capable of but until I have a serious upgrade, being able to play it through the Sharp would do me fine.

(B. P., via email).

Have a look at the inverse RIAA network published in the June 1994 issue. This is a passive network which converts RIAA phono inputs to line inputs.

We can supply the June 1994 issue for $8.80 including postage.

Problems with smart card kit

A few days ago, I purchased a Jaycar Smartcard reader/programmer kit (cat KC-5361). I had no problems assembling the kit and all of the tests recommended in the construction instructions were successful.

I downloaded and installed IC-Prog version 105a and the drivers for NT/XP. I have now spent days trying to read and/or write to the gold card (purchased at the same time as the kit). The settings are exactly as suggested in the instructions (3.58MHz, etc)

When I select read all, the reader returns all zeros. I have since discovered that IC-Prog does this even with no card inserted (or in fact, with no serial connection at all). I understand that a blank card does not return zeros. I have tried writing to the card - this seems to succeed until the verify, which fails at 0000h. When I use the card wizard, it fails at the card reset.

Here is what I have done thus far:

(a) Using the 'Hardware Test" function of IC-Prog, I have tested the levels at the RS232 port on the circuit board and all is well; (b) I have checked every solder connection (26 times) visually and with a meter; (c) I have checked and re-checked every component for the correct value and orientation; (d) I have purchased three new ICs and replaced those; (e) I have purchased a new gold card; (f) I have re-tested the voltage levels as per the instructions; (g) I have replaced the power supply with a 9V battery; (h) I have read and re-read the instructions and the help file provided with IC-Prog; (i) I have tried using another computer with a different OS; (j) I have tried all of this in both SmartMouse mode and Phoenix mode.

The results are always the same. I would be extremely grateful for any assistance you can give to help me resolve the problem.

(G. M., via email).

First up, note that a card that has not been successfully programmed (with the recommended loader) will always cause a "Card reset failed" error when trying to access the EEPROM.

Also, after opening the loader HEX file (but before attempting to write it to the PIC), make sure that the 'CP' (Code Protect) fuse bit is not enabled (ticked). If the PIC is inadvertently code protected, it will always read back as "zeros".

It should be possible to diagnose the problem using the procedure outlined below. Run throughout the tests once without a card in the socket and a second time with a blank Gold card inserted.

Important: the following tests assume that the board has successfully passed the voltage checks described in the kit instructions:

In PIC programming mode, four signals are controlled by the software to perform the necessary erase/program/verify. These are DATA OUT, DATA IN, CLOCK & MCLR/VPP. Each of these signals should be examined for correct operation. This can be achieved with an oscilloscope or logic probe and the "Hardware Check" dialog, accessible from the "Options" menu.

Testing the DATA OUT & DATA IN signals is straightforward. When you check (tick) the "Enable Data Out" option, a corresponding tick should appear in the "Data In" box. This is because the two are connected together at the junction of the 4.7kΩ & 470Ω resistors (connected to IC3e & IC3c). Verify that the signal arrives at the card socket's DATA (C7) pin.

The CLOCK signal can be checked by monitoring the card socket's CLK (C3) line and toggling the "Enable Clock" line. The signal should toggle between a valid logic '0' and logic '1'. Likewise for the MCLR/VPP (C2) line using "Enable MCLR", but this time the signal should swing between 13V and 0V.

Of course, the mode switch (S1) must be in the "PIC Programming" position (OUT) for the above checks.

Using the fuel mixture meter in an old car

I have built a fuel mixture kit but I was going to use it on an older pre-unleaded engine (1972 vintage car). I realise that the EGO sensor would be adversely effected by the lead tetraethyl additives that were used but what about the newer fuels; ie, the super lead-substitute fuels that do not use the older lead additives?

Can these newer fuels, that are specifically designed for pre-unleaded vehicle engines, be used longer term with the zirconia sensors or is it only short term as described?

(R. Z., via email).

Just use LRP (lead replacement petrol) and it will work fine.

Ethics of vintage radio restoration

I am attempting to restore a sentimental valve radio and have a question. On top of the chassis, there is a can capacitor, labelled Ducon 8 mfd. What are the correct "vintage radio ethics" for replacing this? Do you leave a hole there and replace it with an axial capacitor or try to get a capacitor of that voltage and dimension to replicate the original?

(C. B., via email).

What most restorers try to do is to preserve the look of the set, as seen from the top of the chassis. Therefore, you should leave the faulty capacitor on the chassis (but disconnected) and install the new (much smaller) one under the chassis.

You can buy products mentioned in this article here : KC5191 : JACOB`S LADDER SC 9/95