Roman,
I've just finished playing around with serveral
methods of hooking up a pic to vehicles VSS.
I'm know EE by any means but here's what I came across.
I started by making my own vehicle speedo with LCD
output.

The sensors I played with only produced a few AC volts.

Trying to use cheapest, least amount of parts
with op amp, diodes, resisters, etc. to create a zero
crossing config I could never get to work (maybe someone smarter
could) Tried configs with serveral diferent op amps etc.

Main problems;
Noise, Noise, Noise.
Mostly ground noise causing a lot of chatter.
(yea, I know what your thinking, good signal filter,
caps, offsetting, etc., thats what I thought too)
So you will end up trying to create multi-level
op amp noise filters, tried several different zero crossing
circuits, good luck. I had none.

Also since I was taping into the wires directly
while still in use for vechiles computer,  impedance,
drawing to much current etc. problems.
Vehicles computers are very sensitive.
To isolate you start increasing inline resistance
and lose to much for your op amps, less restance and you start
screwing up you vehicles computer, etc.

The only solution that ended up working (for me)
was also mentioned by charles, using a zero
crossing device, ie LM2907/2917
these ic's are very signal sensitive, very configurable
as far as shaping your signal output and allow offset.
With alittle tweaking these chips turned out quite reliable
signals.

I would suggest a bench set up to start.
I purchased a VSS sensor from my local ford
dealer for $14.00 added a cheap dc motor $3.00
a washer with a notch cut in it and a pot for variable speed.

Just beware, when all looks great and you move to
in vehicle testing it falls apart. Noise, Nose, Noise.

I'm now working on putting together a portable hand unit
to start documenting VSS signals from different vehicles.
I had no luck finding such info. If you or anybody does, I sure would
be interested also.


> Thanks Charles! This is the situation I'm in. Most
> of the motorcycles use a hall sensor with a nice
> squarewave output. We are trying to expand our range
> to suit the rare bikes (and MOST cars) that use
> a coil sensor.
>
> I can build a front end amp and use some type of
> zero corssing detector, but obviously it would be
> nice to know what average ac voltages these coils
> produce in most normal cars. I was sort-of hoping
> they would produce a few volts so I could just
> connect it to the PIC with a diode and simple
> filter. Adding an amp will mean a new PCB manufacture
> which is an added expense...
> -Roman
>
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