Need a circuit that can capacitively or inductively detect a spark from an IC engine.

Lawson

I need a circuit that can capacitively or inductively detect a spark from an IC engine for a project. Google was unhelpful, figured I'd ask a much smarter knowledge engine.

I've got a little hour meter for a motorcycle that senses the spark with an insulated wire wrapped around the spark plug wire. I'd like to do the same. Right now I'm assuming I can hook the wire "directly" to an input pin with a weak pull-down and it would work. (I'd include a protection network) Still I'd rather start with a proven and tested circuit.

Lawson

kwinn

That's one of the three typical way of doing it. The other two are a metal sleeve around the plug/distributor wire or a connection to the coil. Regardless of which method you use a protection network is necessary. On a 12V car system this was done with a high powered resistor (5W 100K IIRC) and clamping diodes to ground and +12V.

It's been a long time since I played with that sort of thing, so the resistance value may be off. Try searching for some articles on building an electronic or digital tachometer. They were typically done using a plug or distributor connection.

sidecar-racer

On newer engines (FI) quite often there is a signal for tach which is 12v square wave, simple from there

ctwardell

This might be useful:

http://www.edn.com/design/other/4325366/Spark-detector-uses-proximity

C.W.

Erlend

You could also tap into the noise that is bound to be on the 12v. A small capacitor would pick up the hundreds-Hz signal which originates from the ignition system. It would probably be a few tens of mV amplitude.

Erlend

PJAllen

AM radios have an uncanny ability to couple such impulse noise.
It's almost magical.