Re: [alfa] Coil negative terminal waveform

[webb.p@xxxxxxxxxxx]

Joe,

This can be measured on your GTV6 with a scope.  It's a 12v square wave.

Easy enough to build.    Use a 555 timer and 47K pullup resistor to simulate the signal.  Feed that to a 330 ohm pulldown resistor into an optoisolator to get a clean pulse generator.

I can forward you the schematics for the MegaStimulator, or even lend you my stim to generate the signal.  I can also forward you the schematics for the MegaSquirt tach signal using the optoisolator into the HC08 DAC.  It should be pretty easy to bang out some code to read the DAC and output it to a screen using a MAX32 serial IC.

-Peter

> I have a fairly open-ended assignment in one of my classes where I 
> need to design a simple circuit with a microcontroller.  I'm 
> considering making a tachometer.  (Yes, I know this can be done 
> without a microcontroller, but that's not the point.)  I know that 
> electronic tachs get their input from the negative terminal of the 
> ignition coil, but I don't know what they're actually measuring. 
> Frequency of some wave?  If so, is it some kind of waveform that 
> could be replicated in the lab with a signal generator?
> 
> Thanks,
> Joe
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