[russell mcdonnell]

Hi Folks,

I've got a Freeduino in mostly working order and just need a decent VSS and INJ signal. I have broken out the injector signal from the Motronic DME in my 1989 Porsche 944, and I thought I'd get a few ideas about suitable conditioning. I've attached some scope traces at idle.

So a pulse goes low from about 14V to close to 0V when the injector is fired, and this pulse is around 10us low (0V), 20us high (+14V) repeated for around 1.5mS when the pulsing turns off (second trace). The big spike is back emf as the injector turns off, I'm guessing it takes a further 500uS until the pintle shuts.

I'm assuming I need to turn the low and fast pulsing for 1.5ms into something that ideally is a single pulse high for 1.5ms providing +5V as an input for the INJ signal to the Mpguino, and this signal needs to track any injector pulse width changes.

I have some idea of using a retriggerable 555 timer, to give me a pulse of say 30us, that is retriggered by any further low going pulses. Any other ideas, methods or suggestions, accepted wisdom etc.

Cheers
Russell