Line output adaptor for iPod player

Here is an idea for a project: an audio adaptor from a 30-ohm headphone output to line input. There are so many iPods and stuff with headphone-only outputs in use now. It would be nice to connect it properly to bigger systems. (R. S., Tanunda, SA).

Such an interface would be only a resistor or two, no gain being required. You would just need a 33Ω or to simulate the headphone load and perhaps a 1kΩ or in series with the line output.

Electrical problems in old Commodore

I am trying to help my daughter who has advised me that the headlights on her 1986 Holden Commodore are very dull and she is finding it hard to see properly at night. Other than tell her to drive on high beam and see if other drivers react, can you advise what she could do? Much appreciated. (B. S., Penrith, NSW).

The first step would be to replace the lamps and then clean the reflectors. That done, check that all connections in the circuit are clean and low resistance – you might even have to replace the headlight relay if its contacts are worn. Check its socket contacts as well.

Also check the battery and voltage regulator to see that they are putting out at least 13V when the engine is above idle. On any car that is almost 20 years old, the whole electrical system probably needs a thorough checkout. It might be a job for your local auto electrician.

Possible error in table lamp dimmer

I was having a close look at the remote-controlled table lamp dimmer in the July 2005 issue and believe that there is a serious error in the circuit. I am sure you would have already detected it as I can’t see how the project would work.

On page 29 of the magazine, the circuit shows the top power line as being both +5V and 240VAC, in effect. I was wondering if the line should have a break between, say, the 2.2kΩ resistor on pin 4 of IC1 and the Triac. Perhaps I have missed something but it looks like there is no 5V rail, as this line comes straight from the 240VAC mains. This would mean that pin 14 (Vdd) is at 240VAC potential. Have I missed something?

I still enjoy the articles regardless; always learning something.(D. W., via email).

This is not an error. The 5V rail in the circuit floats from the incoming Active line of the 240VAC mains, as you suggest, and it is derived via the 220nF 250VAC capacitor, 1kΩ 1W resistor and zener diode ZD1. This is explained on page 31 of the article.

Using the Coolmaster as a heater control

Could the Coolmaster fridge controller from the June 2005 issue be used to switch a heater instead of a cooler, with minor changes?

My understanding of electronics is limited but could it be as simple as swapping the inputs of pins 2 and 3 of the LM311 or is there a different chip which operates in the same way but with the output inverted? Alternatively, is there an equivalent to the LM335Z that has an inverse temperature response? (A. M., via email).

Your surmisal is correct. If you want to use the Coolmaster circuit to control a heater, this can be achieved by reversing the connections to input pins 2 and 3 of the LM311. This will be a bit tricky in practice though, as the PC board is quite small and congested, particularly in that area.

Note that there are two tracks connecting to the pin 2 pad and both will have to be swapped over to the pin 3 pad.

Coolmaster for motor protection application

I would like to modify the Coolmaster temperature controller (June 2005) so that it will switch off the 240VAC power line when a temperature sense point of 65°C is reached. If this is possible, I will purchase the kit.

The application is to protect the winding of a 240VAC single-phase sanitary pump motor. According to the supplier, on full load the current draw of the pump is 5A and at start up it is at least 15A. The existing "protection" of a small bimetallic switch on the active phase has failed to protect the winding. The contacts welded together, resulting in a cooked motor.

Could I swap the inputs to pins 2 & 3 on the LM311 so that a rise in temperature would turn pin 9 low and ultimately, switch the Triac off? Would I need to uprate the Triac? Or should I leave the sensing circuit alone and use the MOC3021 output to switch the Triac off?

When you investigate the price of commercial electronic motor protection relays which use a PTC thermistor I think there would be a ready market for such a kit.(T. J., via email).

We would not recommend modifying the Coolmaster to protect a motor winding. Instead, we would suggest the use of a 60° thermal circuit breaker, with a rated current of 10A. These are available from Altronics, Cat No S-5600. Their website is www.altronics.com.au.

More current for Luxeon driver circuit

I recently obtained one of the new Luxeon III red LEDs for some optical communication experiments. To efficiently power it, I bought one of your Starpower (April 2004) kits.

However, I’ve discovered that the red, red/orange and amber Luxeon IIIs can take a lot more current than the older blue/green/white ones. 1.4A is the suggested operating level compared to 1A for the older ones.

The Starpower is designed for a maximum current of 1A. Is there a way to modify it to provide 1.4A for the red Luxeon III? (D. S., via email).

The StarPower can drive a single red, red-orange or amber Luxeon III Star at maximum current (1.4A) with a few modifications, as follows:

(4). Use 1mm wire for the inductor (L1) and wind on only 16 turns, spaced evenly over the core area.

Visual Basic for electrocardiograph

In the February 2005 edition, you published an article on the "USB-Controlled Electrocardiograph". On page 24 it said that the program was programmed with Visual Basic version 6. I have Microsoft Visual Basic and I was wondering if there is a difference. Secondly, no matter how many times I ask the Windows Office Assistant, I cannot find any code relating to the USB cable. If you could give me some advice, it would be greatly appreciated. (J. F., Bendigo, Vic).

There are quite a few versions of Visual Basic. There was the original version, for DOS-level programming (called VBDOS), and then six different versions of the Windows-based version: Visual Basic Versions 1-6, each of which was an upgraded version of the one before. More recently, they were all supposedly replaced with VisualBasic.NET, which is the only version sold nowadays. However, many of us prefer to keep using VB6, the one used to write the ECG program.

Actually, they make two different drivers available but we used the one which makes the USB port you connect to behave like another serial data port (ie, a virtual COM port). This allows you to communicate with the device in Visual Basic using VB’s plug-in serial data control DCOM98. This doesn’t actually come with VB6 but you can download it from Microsoft’s Visual Basic website.

Radio interference to Driveway Sentry

I have successfully built the Driveway Sentry (November 2004), from a kit of parts supplied by Jaycar. The project has worked well, installed at the start of our 70m driveway on a 5-acre property; just the job for the situation where the main living area in the house is blind to the driveway.

There is just one problem: every time I transit on the 2-metre amateur band, at even low power levels (<5W), the alarm goes off! Transmitting on HF frequencies, even at 100W, has no effect. I’ve tried various solutions like placing ferrite beads on all the wires leading into the control unit, bypassing the power and buzzer leads with various values of ceramic capacitors, etc, all with no effect.

The 2-metre transmitter is a base unit located well away from the sensor, while the aerial is mounted well off the ground and properly matched. The odd passing taxi has also set it off. Any suggestions?

I am toying with the idea of replacing the box with a metal one but that won’t have much effect if the RF is getting in along the leads. It takes the shine off what is otherwise a very reliable design. (N. D., Perth, WA).

We doubt that the 2-metre signals are getting into the Sentry via the sensor or sensor cable. It is more likely that it’s getting into the PC board either via the power supply or by direct radiation through the plastic box.

So your idea of fitting the board in a metal shielding box is probably the right way to go. We expect this to stop the false triggering but if it doesn’t, you could try fitting ferrite beads on the sensor cable wires right next to the terminal block on the PC board.

Digital audio adaptor for home theatre

I have several pieces of equipment that have coax and/or optical audio outputs. My home theatre amplifier has only one coax and one optical input. At the moment, I have to unplug one piece and replace it with another if I want digital sound.

Is there a coax or optical adaptor available to build that would allow all pieces to be connected at the same time? I would only ever use one sound source at any one time so I am basically looking for a unit that saves the need to swap plugs. (R. T., via email).

You can buy an optical switcher from Jaycar, Cat AC-1675 for $19.95.

Noise-cancelling in the home

Have you ever had a project with regards to noise cancellation? I live near a very noisy highway and have heard that the noise can be nulled by recording the sound then playing it back through an amplifier in reverse. Any chance of such a project? (J. G., Perth, WA).

Such noise-cancelling techniques are practical in noise-cancelling headphones and in cars such as the latest Honda Legend but it is probably not practical in a larger environment such as a room. If it was to be done, it would involve having a microphone outside the window to pick up the noise which would be then amplified and reversed in phase to the noise in the room.

Folding number plate controller

I went to an electronics store with the question of how could I make number plates on my car fold down. I was told the best option would be to use a stepper motor. I would like the motor to turn the plates either through 90° or 180° but do not know how to construct the circuit for such a thing. Could you please help me find a solution? (E. J., via email).

It is probable that folding down the number plates of a registered vehicle is illegal. Having said that, if you wanted to do it (and had a legal reason), it would be easier using servos. Have a look at the tilt and pan control circuit in the January 1998 issue.

Charging VRSLA batteries

I read with interest some of your questions and answers on the topic of sealed lead acid batteries and the charging thereof. Are you able to point me in the right direction for a concise explanation of the different SLAs available, the best chargers for each and the don’ts associated with each?

I work in a golf buggy shop and am continually confronted with questions on VRSLAs, AGM and gel cell SLAs and what charger suits what. I understand the charging requirements in particular for a gel SLA are different to that of a normal SLA. Often, customers come in with Arlec or Projecta type chargers and it is difficult to advise if they are suitable for their needs.

Any ideas how I can determine if a customer’s charger is doing what it should and what the different SLAs require? (L. T., via email).

There are no easy answers. You need to see the battery maker’s specs to see the recommended charge rates and end voltages. Most simple car chargers are not really suitable for SLAs, as they will ultimately over-charge them.

Viewing DVDs On A VGA Monitor

I basically need to connect my DVD component video signals to the VGA connector of my PC monitor. I’ve found the article on "Component Video to RGB Converter" (SILICON CHIP, May 2004) interesting. However, this article is mainly for TVs with RGB and composite sync input.

In the case of a PC monitor, the VGA connector is actually RGBHV, where the sync signals are separated. So I am wondering if I can modify the circuit like this: (1) use the LM1881 pin 1 (composite sync) as the horizontal sync output to the VGA; and (2) use the LM1881 pin 3 (vertical sync) as the vertical sync output to the VGA.

Do you expect there will be problem with this circuit? The problem I can think of is that the PC monitor is expecting a sync rate which is different from what is coming out of the DVD. I’m not quite sure about this and your help is appreciated. (Andy, by email).

It won’t work. VGA sweep speeds are radically different from PAL signals. The easiest way is to use a computer with a DVD player.

When Is The Battery Zapper Finished?

I have found reading about the Lead-Acid Battery Zapper in the July 2005 issue interesting. One question though: how does one know when the battery is rejuvenated (after using the project)? (M. P., Christchurch, NZ).

Good question. It might take several days or more of zapping to get a result. Then you need to test whether the battery will accept a charge; ie, a charge of several amps or more, that takes a reasonable time for the battery voltage to come up to 14V or so.

Notes & Errata Fig.1 (left): the parts shown in red (D4 & ZD2) are necessary to protect the IRF540N Mosfet from voltage spikes. Lead-Acid Battery Zapper, July 2005: the parts list on page 43 states that Q2 is a 60V device, whereas its VDSS rating is actually 100V. Also, on the circuit diagram (Fig.2), the pinout diagram for Q2 is labelled "IRF640N" instead of "IRF540N". In certain situations, the Mosfet (Q2) may fail due to excessive drain-to-source voltage. To ensure that this cannot occur, a clamp circuit should be added to limit the peak voltage to a safe level. The clamp consists of a 75V, 1W zener diode (ZD2) in series with a UF4004 ultra-fast rectifier (D4), connected between the drain and source of Q2 (see Fig.1). A modified PC board design that accommodates these extra parts will be available in the future. For those that have the original published PC board design, the two components are easily added to the copper (underside) of the board, as shown in Fig.2. Fig.2 (right): the extra parts can be added to the copper side of the PC board, as shown here. The anode lead of the UF4004 is soldered to drain pin of Q2, whereas the anode of the 75V zener is soldered to the source pin of Q2. Their cathode leads are then trimmed and soldered together. Note that both components must be positioned flat against the PC board surface, with their leads shaped roughly as shown. Overall lead length should be kept to a minimum, and as a final step, the diodes can be glued to the PC board to ensure long-term reliability. Finally, we recommend that a switch be fitted in series with the positive battery lead to allow the unit to be isolated during connection and disconnection. This eliminates the possibility of arcing at the battery terminals. Any miniature mains-rated switch would be suitable, such as the Jaycar SK-0975 miniature toggle switch. Fig.3: the on-off switch can be mounted in the case next to the fuse. The 10nF capacitor across the switch reduces contact arcing. A 10nF 100V polyester capacitor (Jaycar RG-5065) must be fitted directly across the switch terminals, as shown in Fig.3. Coolmaster Fridge/Freezer Temperature Controller, June 2005: a 2.2kΩ resistor was erroneously included in the parts list and is not required. Serial LCD Driver, August 2995: transistor Q2 on the overlay diagram (page 76) is shown reversed. The various photos and the silk screen on the PC board show the correct orientation. Carbon Monoxide Alert, August 2005: the 4-band colour code listed for the 470Ω 1% resistor is incorrect. It should be yellow violet brown brown. Automatic Lamp Dimmer, September 2005: the 4-band colour code listed for the 470Ω 1% resistor is incorrect. It should be yellow violet brown brown.