Loudspeaker design software

I am looking for articles on subwoofer and speaker en-closures. There was an article in the June 1996 issue on BassBox loudspeaker software. I would like to know if you subsequently published a design using the compound speaker concept featured in this article, as I would like to build a subwoofer enclosure using two 10-inch subwoofers for my car. If not, are there any plans to feature something along those lines in the future? (C. E., via email).

We have featured only two sub-woofers designed using the BassBox software. They were the Bass Barrel in the August 1997 issue and the Bass Cube in the April 1999 issue.

Flickering flame doesn’t flicker

I recently built the Flickering Flame as described in the October 1997 issue of SILICON CHIP and have a problem trying to run it off mains power using a 240VAC AC transformer rectified to 12V DC. The problem is the light does not flicker; it just stays on. But when I connect it to a car battery it works cor-rectly.

Could you please help me with this problem? (G. W., via email).

Our guess is that you have insufficient filtering on your rectified DC supply. You would need a capacitor of at least 4700mF at 25VW.

Temperature controller can’t heat & cool

I gather from the article on the Switching Temperature Controller in the August 1999 issue that can only run one Peltier Effect device at once. Is this so? So in order to keep the inside of an Esky used as a brooder for raising baby birds, two circuits would be needed – one for cooling and one for heating?

I assume that a Peltier device mounted on a CPU cooling fan heat-sink would blow cool air? (T. A., via email).

You are right in that the circuit can only be used for heating or cooling. If you try to do both, both the heating and cooling sides of the circuit will be powered all the time which is highly inefficient. If you wanted to do heating and cooling, to maintain a constant temperature for a wide range in ambient, the circuit would have to be extended with extra comparators to switch in the heating or cooling function.

A Peltier device mounted on a heatsink could be used to blow cool air but it would only be slightly cooler than ambient.

Setting up the capacitance meter

The Digital Capacitance Meter described in the February 1999 issue looked very useful to me, especially with its pF range. Unfortunately, having built the unit, I cannot null the output of IC2a and this ruins the low range readings. For testing, I have numerous 2% capacitors ranging from 47pF to 0.9mF, a borrowed capacitance meter, a DVM, oscilloscope and frequency counter. I have noted the Errata in May and June 1999 issues and have checked the unit carefully. The voltages seem correct as do the scope waveforms.

It can be made to work tolerably well on the nF and mF ranges but is not acceptable on the pF range. The voltage at pin 11 of IC2a does not dip (to 5-10mV) and rise again but ranges from 66-89mV when varying trimpot VR1. Changing IC1 alters this slightly but does not fix the problem. The frequency at pin 8 of IC1 with the first 74HC132 measures 12,124Hz and 12,400Hz and with the replacement 11,109Hz and 10,900Hz, approximately. The text refers to 16,160Hz and 16,000Hz. Is this significant? (R. B., Flaxton, Qld).

We will answer to your queries in order:

(1) The frequency is not critical but if it is too low then the readings on the mF range may be erratic. Once you get the unit working, reduce the value of the .01mF capacitor at pin 2 of IC1a until the frequency is closer to the nominal value of 16kHz.

(2) The varying stray capacitance of different PC boards, especially if they have a screened overlays and solder resist can mean that VR1 may not have sufficient range. The cure is to increase the 12pF capacitor on pin 13 of IC1d to 22pF or 33pF until VR1 can be set close to centre.

(3) As you have an oscilloscope, simply clip the probe on pin 11 of IC2a and carry out the set zero adjustment. The pulse width at pin 11 will get narrower and narrower until it disappears, then if you keep adjusting VR1 it will reappear and get wider. The correct adjustment is when it just disappears.

Problem with remote central locking

In order to add remote central locking to my car, I purchased the UHF remote control kit, as published in the January 1993 issue of SILICON CHIP. I also purchased a Jaycar LR-8835 Power Lock Relay and an LR-8833 Slave Door actuator.

The problem I have is that when the transmitter is 30cm or more away from the receiver, the channel that is being operated starts bouncing on and off erratically. This in turn, via the Power Lock Relay, pulses the actuator in the same direction. With the trans-mitter within 30cm of the receiver, the actuator operates normally.

When the actuator is removed from the circuit, the receiver and Power Lock Relay operate fine, even when the transmitter is a good distance away. This happens on the test bench and when fitted to the car.

I have one channel doing unlock and the other doing lock. The receiver is set up for momentary operation. I have earth coming from the two NO contacts in the receiver and going to the Power Lock Relay brown and white inputs. Some things I’ve already tried are: filtering the receiver’s 12V input, supplying power for the receiver from a different source, a new transmitter battery and even wrapping the actuator in aluminium tape.

The car already has central locking but the driver’s door only has a microswitch that operates the other doors, no actua-tor. The new actuator operates the lock mechanism which in turn operates the microswitch.

I have actually gotten the system to work using the NC receiver outputs. Now the Power Lock Relay inputs are normally at earth but when a button is pushed, the Rx operates and removes the appropriate earth from the Power Lock Relay. When the button is released and the receiver switches off, the earth is then reap-plied to the Power Lock Relay which drives the actuator. But I want to get it to work the way it’s supposed to so I hope that you will be able to help me. (S. B., Amberley, Qld).

Your problem appears to be with the remote control receiver resetting as the heavy current drawn by the door actuators reduc-es the supply voltage. This can be cured by several means. First-, you need to use a separate supply lead for the actuator positive supply. The receiver will then have minimum voltage drop when the actuators are powered.

Second, the receiver circuit can be improved to reduce the incidence of resetting. This involves reducing the 6.8V zener diode dropping resistor from 1.8kW (R4) to 390W. This will maintain the zener voltage even if the 12V supply drops to 9V. You can also replace the 10mF capacitor C4 with a 100mF 16VW electrolytic to improve supply rejection.

You may also need to connect a large value capacitor across the door actuator solenoid to damp down transients. Also a re-verse connected diode (1N5404) across the actuator coil may help.

Converting a standard PC power supply

There has been some discussion this year on using old computer power supplies as general purpose bench units but there are many variables; one that I have hit is that one power supply would not start without a decent (15-20W) load on the 5V line.

One comment that I saw was that one reader rebuilt the 5V section using the 12V components to get a 220W power supply at 13.8V (after adjustment of the output voltage). That is one hell of a good bench supply for anyone involved in car radio, amateur radio, CB or similar activities.

It would be a good supply for 12V garden lighting without the risk of the voltage going up as lights blow. I have a 100W transformer driving a string of 8W lights and if more than three blow then the rest will blow within 15 minutes!

PC power supplies are available here in Canberra for $5 each with one proviso; you have to take the whole computer! Can you devise a circuit board and parts list that a mid-range experimenter could work from to build such a beast. Tracing out a switchmode power supply is beyond me; I know because I have tried. (B. W., via email).

We have had a look at the idea of a circuit to convert a standard PC supply to something more useful but the problem is that all these supplies are different inside, even though they all tend to use one or another standard switch-mode IC. The only way we could do it is to specify a particular switchmode PC supply and then go from there although that tends to defeat the purpose of letting people use any surplus supply.

Loud direction indicators wanted

I need a simple circuit for people who are hearing im-paired, to amplify a vehicle’s blinker noise, as the "click click click " of a normal can under the dash is too soft to be heard. (J. C., via email).

Why not just wire a buzzer so that it is powered from both sides of the traffic indicator switch can via a pair of diodes? That should do the trick.

DC-DC converter
for military gear

Have you ever designed a 12V to 24V converter? I wish to use some military equipment in a "civilian" car for demonstration purposes. Trouble is, all our communications gear is designed to run off 24V DC nominal (28V with the vehicle running). Any ideas? (I. B., via email).

One possibility may be to modify the 2A SLA battery charger (published in the July 1996 issue) so that it delivers 24V in-stead of 13.8V. You would do this by changing the 22kW and 2.2kW feedback resistors to 39kW and 1.8kW, respectively. You would also need to add a 4700mF 35VW capacitor to the output. We es-timate that it should be good for about 1A at 24V. (Note: we have not tried this).

Programmable ignition for a Landrover

I was reading the June 1999 edition and I came across the programmable ignition article. The Lumenition control module on my Landrover has just failed and I wondered if it would be possi-ble to replace it with a PIT module and adapt the optical pickup that is already fitted to the vehicle. (N. W., via email).

Yes, it is possible. We published a brief note about using the Lumenition module in the May 1994 issue.

DC-DC inverter
for car amplifier

I wish to build an amplifier to put in my car. It needs supply rails of ±37.5V or ±40V. Do you have a circuit design for a DC-to-DC converter to give the required supply rail from a 12V car battery? (M. N., via email).

We published a 100W DC-DC Converter for cars in the December 1990 issue and a 600W design in the October & November 1996 issues.

Display problems
on signal generator

I built the Low Distortion Audio Signal Generator described in the February & March 1999 issues of SILICON CHIP but it has a problem I can’t explain. When I went to set up the generator, the oscillator worked well but the display didn’t. I eventually found that the 0.18mF capacitor associated with S2 and IC1b was earthed and suspected that it wasn’t meant to be, according to the circuit diagram.

I cut the track and then the display worked well, except on the 10Hz to 100Hz range where it dropped to 0000 at about 3/4 setting. This range could be made to work by adjusting VR3 fully counter-clockwise. But in doing this, the other ranges had a point midway in their range that dropped back to 0000. I did notice that if I touched the back of 0.18mF capacitor associated with IC1a, the display worked perfectly on all ranges.

I have since put a 10MW resistor across this capacitor and it works fine. I am very happy with the end result but cannot for the life of me work out what I have done to cause the problems mentioned. I checked all the components at least twice with the multimeter. Maybe you can shed some light on this problem? (A. B., via email).

With regard to the 0.18mF capacitor being earthed on your PC board, apparently one of the PC board manufacturers decided that a shield track (earthed) should have been connected to an adjacent pad on the PC board and so they changed our original pattern. This meant that some kits did have a faulty front panel board. This was corrected on kits as soon as the error was discovered.

Unfortunately though, the published pattern for the front panel (page 64, March 1999 issue) does show a thin line, making the connection from the ground track to the 0.18mF capacitor pad. This is due to a glitch which sometimes occurred when the Protel file for the artwork was imported into our drafting package, Generic CAD. The component overlay diagram on the same page does not exhibit the glitch. The original artwork sent to board manufacturers also did not have the shielded track connected.

The lack of output at the low frequency end would mean that the LDR was not receiving sufficient light to maintain control. This was probably due to the IR LEDs not providing full light coverage over the LDR surface. If you are happy with the result with the 10MW resistor across the 0.18mF capacitor, then leave the oscillator as is.

Command control decoder

I am building the February 1999 version of the Command Control Decoder For Model Railways but I am having difficulty finding the required BD433 and BD434 transistors. Any suggestions? (K. R., via email).

You can substitute transistors such as BD675/677/679/681 or BD263 for the BD433 and BD678/680/682 or BD262 for the BD434. These are readily available from kitset suppliers.

Waiting for turbo timer defeats purpose

I have just built the turbo timer as published in the November 1998 issue and tested it on the bench. It works fine. I then did a temporary hook-up to my car. Guess what? You cannot take the key out of the ignition while the engine is running, so one has to sit while the timer runs out.

I am certainly not going to leave the key in the car while I do my shopping. Anyone else having the same problem? Oh, the car is a 1992 Nissan Bluebird AWD Turbo. (G. W., via email).

If your turbo timer needs the ignition switch on to run, you have taken the +12V from a point switched by the ignition. You need to pick up +12V from a fuse not switched by the ignition key.

Jumbo LED clock problems

I am having many problems with the Jumbo LED Clock described in the March 1997 issue. I obtained the displays from Jaycar and I had to drill new holes in the board as they did not line up correctly. The project did not work and I eventually found out that the displays had different connections. I rewired the displays using separate wires between the two boards.

I could not find a supplier for the watch crystal, so I obtained six from old watches that I had to hand. Checking with my DFM, one crystal oscillated at 16kHz, one didn’t work and the other four worked at 31.25kHz. The clock worked but it ran slow, losing three seconds each minute. With the oscillator running too low, I would have thought it would have run too fast.

Pressing the hour button clocked up the hours OK and the AM-PM indicator worked. Also the 1-second decimal points worked. But on first switch on, it indicated -004, the righthand number being any value on switch on.

When pressing the minute button, the number clocked up while the button was pressed but on release the numbers all changed to an arbitrary figure. Adjusting the oscillator trimmer from minimum to maximum only varied the frequency from 31.35kHz to 31.25kHz and the oscillator stopped with the trimmer set at exact minimum. I used machined IC sockets for all the ICs so I can change them easily. I have an oscilloscope and a DFM. I used an earth on the PC and a wrist strap as I thought the ICs might be static sensitive. (S. F., Yangebup, WA).

We suspect that the 4526 prescaler ICs, IC2 & IC3, may be causing the problems of strange results from the minute pushbutton and incorrect timekeeping.

Check that the DP1-DP4 inputs for IC2 and IC3 are correctly tied to the ground or positive supply. Erratic behaviour may occur if they are floating. Also check for shorts between tracks around these two ICs. You should compare your PC board pattern with the published pattern (page 49, March 1997) to check that you have not soldered two pads together.

We are not aware that the pinouts for the large 7-segment displays are any different to the ones we used in the prototype. These pinouts follow an industry standard.

The exact frequency of operation for a crystal oscillator cannot reliably be tested with a probe and frequency meter. This is because the probe’s capacitance can load the crystal and slow down its frequency. Normally, if you want to reliably measure the frequency of a crystal oscillator, you must do it via a buffer stage.

A suitable crystal can be obtained from Farnell Electronics, phone 1300 361 005. Their catalog number for the crystal is 569-914.

Sync output for TV pattern generator

I would like to know if the Colour TV Pattern Generator described in June & July 1997 has or can have a separate sync output as well as the composite video. I have an application that requires this. (D. P., -via email).

The composite sync signal is available at pin 16 of IC10. Since its amplitude is 5V peak-to-peak, you may need to attenuate it to the required level for your application.

Notes & Errata

Daytime Running Lights for Cars, August 1999: a modification to allow the circuit to be used with cars having headlight switching in the negative line is published in Circuit Notebook this month.

PC Monitor Checker, August 1999: circuit modifications to give more ideal scan frequencies are published in Circuit Notebook this month.

WARNING! 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.