Measure Pulse Width / Duty Cycle of an Injector to drive a pump

Yes, but are the oscillations constant width? If so, it is quite easy to count them; although, measuring the period is also easy. Just start the timer with the first "high" after the first "low" of longer than 1 mS (or whatever ). Stop the timer when the next expected low is missed.

Gotta run.

John

the back EMF, Do I need to protect against this? eg. diode across the injector coil pins

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My interpretation of the waveform shown is that something (diode?) with a breakdown voltage of ~40V is already in place across the injector coil. With no breakdown device at all the back emf would possibly have been ~ 1kV or more. A reverse-biased diode with a low forward voltage (e.g. Schottky) is commonly used with relays but is less than ideal for injectors because it slows down the coil switch-off.

Thanks alec_t for confirming that, that's one less thing to worry about then. Going to design a circuit on CircuitLab.com and will post first draft once done, Circuitlab offers a testing function but as I plan to use a pic that's not really going work so it will be simply a means to design a circuit. I'll reply back in about a weeks time hopefully with my first draft. Thanks both for all your guidance so far - much appreciated.

Rodp