Reading Secondary Ignition Voltage from car ignition systems

Hi there,

I want to use Arduino to read a car secondary ignition voltage.

Last week I search everywhere and I have not any clear answer to how to read secondary ignition voltage from ignition plug cables.

I had a handheld device which can do this and I need this data in my computer.

My handheld device manual says, it has capacitive sensor to read secondary ignition from ignition plug cables.

Anyway, secondary ignition voltage can up to 50kv dc.

Is there any way to read this data using with Arduiono.


The basic principle is a capacitive divider - just like a resistive divider except that the formula is C1 / (C1 + C2) rather than R2 / (R1 + R2) for the division ratio. Thus if the pickup probe is 1pF (for example) to the HT lead and you want 0.0001 ratio, C1 = 1pF, C2 = 10nF and a 50kV pulse will appear as 5V pulse across the 10nF - both capacitors take up 50nC of charge.

In practice you'll have to calibrate the pickup probe yourself

You also need protection circuitry such as a string of high-voltage series resistors inline with the probe and a zener diode to ground to prevent high voltage transients escaping into the output.

Also remember modern car ignition systems with capacitive discharge HV generation can easily kill - make sure all the HT leads are clean and in good condition (no cracks).

Thanks for reply,

It seems, there is no basic way (I mean find xyz sensor fit the ardunio or one of those multi sensor shields and program it).

I have some programming background and electronics stil look like black magic.

Could you lead me any useful document for covered this topic.

My best regards.

I'd be cautious then, those high voltages don't take prisoners and protection circuitry is important. There might be an existing meter that you could interface too at the low-voltage side - have you details of your handheld meter to share - there might be a way to connect to it that would be simpler and less risky.