I would like to monitor the ignition voltage on a mid 70's Dodge. I want to ensure that the voltage going into the coil is at the proper level. The car has an early version of an electronic ignition and hall effect sensor instead of points.

The part to read and display the voltage should be easy enough. The difficult part is how to condition the signal.

If this is on the right track do I need zener's at point A to filter out spikes?
If not where to start.

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I gotta question, since ignition coils aren't too picky about input voltage and you can't have anything over 14V, why worry? Hell i've ran my old 1978 oldsmobile engine on as low as 8-9V. Couldn't you just run a wire from your ignition input and use a multi meter?

 

Might work if I had an old analog one.

I am worried about it going too low. This car has had ignition problems since it was nearly new. I bought if from the original owner who said he replaced most of the electrical system about every 20K miles. I want to know when it drops so I can fix the problem prior to carboning up the engine.

The input to the coil is rather noisy. It cycles on and off for each cylinder that fires and perhaps has spikes from the switching. Have yet to take the scope out and look at it.

In time I want to build some digital gauges and this would be a very useful place to start.

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Hi 3V0,

A battery voltage monitor circuit takes care of the voltage going to the coil. Monitoring that you don't know about the ignition voltage supplying the spark plugs.

To find out if that voltage is high enough you must use the HV-voltage output. Wrap 3 or 4 windings of well isolated wire around the HV-cable going to the distributor and connect a small neon signal lamp to it. (You'll probably have to experiment a bit because there are different ignition coils used)

If you want to use that voltage for a digital readout it requires further treatment such as a rectifier and some kind of charge pump connected to the measuring circuit.

Regards

Boncuk