-----Original Message-----
From: Picdude [mailto:picdude@NARWANI.ORG]
Sent: 23 September 2003 15:20
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [EE] (automotive) frequency trigger


> What type of vehicle is it?

A Nissan Skyline GT-R (1997 model)

> Have you really seen (on an oscilloscope, etc)
> that it is a square wave?

Sadly no, my hobbyist budget won't stretch to a scope.

> I say this because most new cars use this speed
> sensor for the cruise control and FI strategy, and usually use a VSS which

> puts out a sine-wave whose amplitude increases with speed.

I don't know about the amplitude, but the frequency definitely seems to be
directly proportional to speed... Readings taken at different speeds all
tally up with the theory.

> Assuming a square wave,  you should be able to simply send this signal
into a
> transistor switch via a resistor (some tens of kohms) and have no ill
> effects, but if you really want hi-impedance, you can use an op-amp.  If
you
> have a sine-wave, then you can use a comparator to square up the signal.

Will resistor/transistor be "safe" enough for potentially dirty power? I'm
concerned that a car is a nasty place to be, and I don't want to be blowing
transistors and pics every 5 minutes....


Thanks

jon

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