Thanks Chris for the good info! Running tests
and gathering info on all the different vehicles
is just about impossible. I have a comparator
design in the works, but not sure if it justifies
the size or cost. I was really hoping someone
would have actually done this and knew the
expected signal level from most standard auto
sensors or something.

I also may not have the luxury of accessing both
wires to the coil pickup, it will probably be
limited to just tapping into the "out" wire
from the pickup as the other wire is usually
12v (or gnd).
-Roman


Chris Eddy wrote:
>
> Roman;
>
> The challenge is to discern the low amplitude sine wave at low speeds.
> Most folks want to pickup to as low as 5 or 10MPH.  The cleanest solution
> is to run the signal into a comparator.  Asuming a 12V supply, generate a
> half supply voltage with a divider and buffer it.  Use this 6V to drive
> one side of the mag pickup.  The return line goes to the comparator.  Of
> course, the other pin of the comparator goes to the 6V line.  Tie the mag
> return to the 6V line with both a resistor (to pull it to center) and
> capacitor (not big.. just to crush EMI).  At higher speeds, the signal
> may get pretty big.  In this case, clamp the return line to the +12 and
> ground lines with diodes.  You must add a bit of series resistance to act
> as burden.
>
> Just sos you don't wind up camping out in the driveway with a cot, I
> suggest that you run some tests on the signal and characterize it
> entirely, including source impedance.  Then you can retire to the safety
> of the lab.
>
> Play with these values until it works just the way you want.  If you use
> a comparator such as LM311 or equal, you can just pullup the output to
> VCC and get a 5V signal.  This ought to satisfy the RB0 pin very nicely.
>
> Chris~
>
> Roman Black wrote:
>
> > Just a quickie, has anyone connected a magnetic
> > coil pickup, as the typical sensor used in car
> > speedos, to a PIC??
> > -Roman
> >
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