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EGO sensor connections
for mixture meter

I have a few queries about the mixture meter kit from Dick Smith Electronics. The recommended oxygen sensor is the Bosch LSM11 which we have obtained. Since there is only one yellow wire coming from the PC board to connect to the LSM11, to which wire does it connect and to what do I connect the other three wires of the LSM11?

The LSM11 has two plugs - one plug has two white wires with male pins and the other has a black and grey wire with female connectors.

(T.S., via email).

You will need to measure the resistance between the wires. There is a heater coil which should measure some low ohm value between two of the wires. The ground wire for the sensor should show zero ohms to the case while the signal wire should be a high impedance to ground.

Probably the two white wires are the heater, while the grey and black wires are for the sensor. The high impedance sensor output connects to the signal input on the mixture meter. The ground connects to the same ground as the mixture meter.

Note that it is not necessary to connect the heater to the 12V supply as the sensor will heat up via the exhaust.

If you do not connect the heater, you can test each wire combination with one wire to ground and the other to the mixture meter until the meter shows the fuel mixture reading.

Mid-band tone control for PortaPAL

I am interested in the PortaPAL amplifier described in January & February 2003. I want to use it for a headphone amplifier for a bass guitar while performing on stage and as a practise amplifier head. Is it possible to add a middle frequency parametric pot onto this circuit?

(R. S., via email).

We published a parametric equaliser in the July 1996 issue of SILICON CHIP. This could be used to replace the bass and treble control circuit. The grounded connections on the circuit would need to connect to the half supply (6V) rail of the PortaPAL. The input potentiometer (VR1) would not be required.

Alternatively, you could add the mid-band circuit for the tone control used in the Guitar Amplifier published in November 2000. Just add the mid-band components from the guitar tone control (VR3, the 2.7nF capacitor and the 12kΩ end resistors) to the PortaPAL tone control circuit.

Concern for Onkyo receiver rating

I have recently purchased a pair of Vifa JV60 speakers (described in August 1995) from Jaycar Electronics. They are rated at 4W. I am having difficulty finding an affordable receiver/amplifier to drive them.

The receiver that I am considering is an Onkyo TX-8511 because I can get it really cheap! However, Onkyo have told me that the amplifier does not support 4W speakers. It is rated at 130W/channel for 6-ohm loads.

This particular receiver, listed in the USA website with the same product code, seems to support 4-ohm speakers however the same product in Australia does not. Could this be because of a design regulation affecting what they can actually say? The amplifier apparently has a large heatsink and runs with a high current which is supposedly good for supporting lower impedance drivers.

The options that I have are either: (1) ignore Onkyo's recommendation and use it with the speakers but be careful with the volume levels and heat build-up of the receiver or add a resister to the speaker crossover to bring it up to 6W; or (2) not use the amplifier at all because it is completely unsuitable.

Given that I am only keen to spend about $500-$700 on an amplifier, what do you think is the most suitable solution to driving these speakers? If adding an extra resistor to the speaker is feasible, where would be the most appropriate position for it to be installed and what resistor would you suggest?

(J. D., via email).

You have two options. Just operate the JV60s with your Onkyo and don't worry - it is unlikely that you will blow anything unless you really turn up the wick and even then you probably will only blow a fuse in the amplifier.

A check of the impedance curve for the JV60s in the August 1995 issue of SILICON CHIP shows that they could have been rated a nominal 6W anyway; the impedance barely dips below 4W at a couple of points in the audio spectrum.

If you are still worried about your Onkyo and want to protect it, connect a PTC thermistor in series with the amplifier outputs. Use the same Polyswitch PTC (Jaycar Cat RN-3470) as we specified in the SC480 amplifier described in the January/February 2003 issues.

Engine knock sensor required

I am looking for a voltage amplifier. The input will be from zero to 250mV and output up to 5V DC. It is needed to convert the voltage signal from engine knock sensors to a higher voltage so the EMU can read the signal (up to 5V DC).

Will an audio amplifier with an AC-DC converter do?

(J. C., via email).

The engine knock sensor described in the April 1996 issue of SILICON CHIP has the essential ingredients you require. These are the amplifier (IC1a with adjustable gain from 2 to around 200) and a DC converter comprising diode D1, a 1μF capacitor and a 1MΩ resistor.

24V SLA charger wanted

I need to trickle-charge two 12V 7Ah SLA batteries in series. Your new charger for the PortaPAL seems ideal with a few modifications for 24V operation.

Apart from a 32V plugpack, I imagine I would have to change VR7 to 1kΩ, the 220Ω resistor feeding the relay would have to be a higher value, the LED current limiting resistor would have to be changed to about 470Ω and the electrolytic capacitor voltages increased to 50V or so. Anything else? Is this an oversimplification?

(B. P., via email).

24V operation would require using a 32V plugpack and changing the capacitor voltage ratings to 50V as you suggest. VR7 should be changed to 1kΩ and the series 1kΩ resistor changed to 2.2kΩ.

The 2.2kΩ resistors in series with each LED should be changed to 4.7kΩ. The relay can be changed to the 24V version (Altronics Cat. S4162A) and the series resistor changed to 1kΩ 5W.

Using 70V rails with Plastic Power amplifier

I am interested in building the Plastic Power amplifier published in the April 1996 issue of SILICON CHIP. I already have a really nice transformer but the problem is that it's going to give me ± 70V supply rails, significantly higher than the 59V specified in the design. My question is, do you think I'll get a way with it?

From what I can tell, all the semiconductors are rated at the higher voltage. If I avoid a 4W load and only run 8W, do you think I'll come in under the SOAR?

(S. T., via email).

We had to go back to the SOAR curves to check out your question. The answer is yes, provided you use only 8W loads, the amplifier is safe with 70V supply rails. But if your speaker impedance curves dip to down below 6W anywhere in the audio range or the supply rails go much above 70V, you run the distinct risk of blowing your amplifier.

If it was our choice, we would not do it. If one of the output transistors fails because of overload, you will probably also lose the speakers in that channel and you could even have a fire! In fact, you should build the Loudspeaker Protector from the April 1997 issue.

Confusion over
diode D3

I refer to the article "Adjustable DC-DC Converter For Cars" in the June 2003 issue. On pages 71 and 72 are photographs showing the assembled circuit board for this project. In both cases D3 is replaced by a wire link and I could not find any reference to this in the text. The text does say that D3 has another purpose besides guarding against reverse polarity and that is to limit the output voltage in the event of a high input voltage.

I assume D3 was not fitted to the development unit on the basis of being not needed for a unit being carefully tested by a competent person but I am left with the lingering doubt as to whether there is any other significance in its omission.

(E. W., via email).

Diode D3 was initially intended to be optional depending on application. The photograph was taken before the decision to keep it in-circuit in all cases.

The unit was tested with D3 in circuit as well as out of circuit.

Using the
4-channel remote

I am helping out a team from Sailability (volunteers who help disabled people to sail) who have a buoy fitted with a beeper which is used to guide vision-impaired sailors around a marker. At this time they are using a 12V reversing beeper which they have to go to and switch on. As a result, it is operating for some time and the constant noise is upsetting some of the locals.

We are assembling the Long-Range UHF 4-Channel Remote Control to solve the problem. But my question is, if another buoy was fitted with a receiver, could the transmitter be used to trigger the two buoys on independent coding or could channels A and B be used?

(F. N., via email).

If you have the receivers in latched mode, you could have up to four for your application, with each receiver operating off one channel.

Another solution for ignition breakdown

I have just read response to the question entitled "Crossfire Problem in Multi-Spark Ignition" on page 92 of the December 2002 edition.

Rather than being crossfire, the problem is more likely to be that the Hall effect sensor is firing prior to the rotor button being lined up with the distributor cap. The vacuum advance will be causing the behaviour. If he removes the distributor cap, there will be obvious spark marks on the leading or trailing edge of the rotor button.

The solution is to remount the sensor back or forwards by about 10 degrees or play with the vacuum advance.

(P. Y., via email).

Reluctor problem with multi-spark CDI

Having completed the Multi-Spark Capacitor Discharge Ignition (SILICON CHIP, September 1997), it appears the triggering from my reluctor distributor is not happening. What could be wrong? The distributor is fine and swapping the reluctor wires over to it does not help.

When power is first applied there is a discharge into the coil, as I can hear it and see it with my timing light. On testing the inverter circuit to your
recommendations, I can measure 300V between the case and the tab of Mosfet Q6.

(W. M., via email).

The reluctor signal sensitivity can be altered by changing the 47kΩ resistor which connects from the cathode of ZD5 to the other 47kΩ resistor which connects to the base of transistor Q8. Use a 200kΩ trimpot first and adjust it until the ignition fires. Then replace the trimpot with a fixed value resistor of the same value.

You can buy products mentioned in this article here :

RN3470 : RXE250 112W POLYSWITCH

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