RPM measurement through the cigarette lighter
Tue, 07/28/2009 - 21:09
I understand it is possible to determine engine speed (RPM) from the AC ripple present on the 12V line of the vehicle resulting from alternator ripple. Does anyone have any more information on this? The reason this is ideal is that you can measure RPM on diesel and petrol engines.
Interesting one this, I know that on of the g-tech pro meters can do this so it must be possible. I should imagine you want a bandpass filter to filter the noise, an amplifier/comparator to square the pulses and then measure the frequency of them.
I just found http://www.kraustelemetry.com/rpm8000/rpm8000-e.html which you might be interested in. It looks like that scaling will be different for different cars however dependant on pulley sizes and number of poles the alternator has.
Keep us updated on any further information.