Help with Engine Spark Sensor to Audio Output Circuit

"John Woodgate" wrote in message news: snipped-for-privacy@jmwa.demon.co.uk...

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to the 555 timer.

capacitive sensor is so simple, - just a few turns of

50 turns of thin wire wound on it. Keep a low-value

I'll just expand on John's answer, with which I agree.

Without considerable care in its construction, an inductive pickup may well function as a capacitive pickup anyway. For what the OP wants to do, those few turns together with a very simple limiting network would be much easier.

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Larry Brasfield
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Tune an AM portable radio between stations and bring it near the engine. It's audible.

John

Reply to
John - kd5yi

Hi All:

I would like to put together a high voltage automobile engine spark sensor that would use an inductive connection to the spark plug wire to drive a 555 Timer circuit that outputs a nominal audio signal.

What I need is a circuit that would inductively interface the spark plug wire to the 555 timer. If anyone has any ideas about this or can give me a web site to investigate, please share. It would be much appreciated. Thanks

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Reply to
bigolow

I read in sci.electronics.design that bigolow wrote (in ) about 'Help with Engine Spark Sensor to Audio Output Circuit', on Sun, 3 Apr 2005:

Why do you want an inductive sensor (which is relatively difficult) when a capacitive sensor is so simple, - just a few turns of wire wrapped round the HT cable?

You could experiment with a ferrite toroid slipped over the HT cable, with say 50 turns of thin wire wound on it. Keep a low-value resistor (10 ohms?) across this winding!

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Regards, John Woodgate, OOO - Own Opinions Only.
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Reply to
John Woodgate

He could be trying to see the fact that the actual spark jumped rather than the fact that the coil made a high voltage.

This still could be easier to do with a capacitive coupling. When the spark happens, a lot of high frequencies are made that are normally not there.

To extend this comment:

If you want to be fairly sure to get the inductive information, you really should use a shield on the cable or over the core. Remember the shield can't form a shorted turn though.

Here's what I'd try:

Copper foil can be obtained but just for messing about use some common al. foil. Stick one edge of the al foil down along the cable. Cover the first 1/2 turn of the foil with a layer of table and wrap about 1.25 turns of foil onto the cable. Tape down the last edge. Connect the toroid to a shielded twisted pair. Use the shield to ground the shield over the cable. At the electronics: connect the conductors to a lowish resistor. Connect the shield to ground.

Connect each of the conductors to the same location on the ground with. lets say, 100 Ohm resistors. Using, lets say, 10K resistors run the signal from the 2 conductors to a differential amplifier made from fairly fast OP-amps.

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Reply to
Ken Smith

) about 'Help

to the 555 timer.

capacitive sensor is so simple, - just a few turns of

50 turns of thin wire wound on it. Keep a low-value

As usual - a total trash answer from a worthless pseudo-intellectual. The c-pickup only tells him the HV was applied and not that it actually fired a spark...

Reply to
Fred Bloggs

"a 555 Timer circuit that outputs a nominal audio signal." What? What kind of an "audio" signal does a 555 put out unless it is running in an a-stable mode? If it's a-stable how do you trigger it without a duration control flip-flop of some kind or possibly two 555's? If it is the spark tick he wants, why not pick it up capacitively as hs been mentioned and amplify in an op-amp? I guess a better question would be what is this for and what is the expected output? Bob

Reply to
Bob Eldred

I think he wants to make a noise box that goes brrrmmm brrrrmmm !

Graham

Reply to
Pooh Bear

Indeed... no 555 needed for that. What about taking a FET with a 1-10M resistor to gate, and couple this capacitively/inductively to the spark plug wire? Then just buffer and amplify the output. Clicks at 6000 RPM (PPS) sound fairly high-pitch...

For something useful, scale these clicks to 0-5V and buffer this into a PICs comparator or external interrupt. Use a ripple-counted TMR0 to time the rising or falling edges, then reciprocate that count to yield the frequency. JAL can do

24 and 32-bit floating-point math and my JAL FP2LCD display routine makes short work of displaying FP values on a LCD. Try it, Mikey likes it!

DISCLAIMER: Don't bother if you don't know what a PIC is. Don't bother if you fabbed PICs fourty years ago. Don't bother if you know it all. Don't bother if you don't know Jack Schitt, or his wife Noe Schitt, or their sons Fulla Schitt, Dip Schitt, Dumb Schitt, or their daughter Loda Schitt...

Reply to
Mark Jones

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