Filtering/Detecting Ignition Noise

Thread Starter


Joined Apr 17, 2009
I am working on a project that uses a reed switch near the rear wheel of a motorcycle running to an interrupt pin on an arduino mounted near the front of the bike. On the way the lead gets fairly near the ignition coils and spark plugs. I have a debounce circuit on the switch which seems to soak up all the noise but without it the interrupt false-triggers every revolution. This makes me think of two things:

1) Can I simplify the debounce circuit so that ALL it's doing is eliminating the ignition pulse? (Maybe all I really need is the cap or diode?). I don't mind debouncing it in software to simplify the circuit.
2) Can I condition the line so I get a reliable ignition signal - this would save me a tach interface.

My basic debounce circuit is shown below. The switch is actually at the end of a 5 ft or so run of insulated wire.