Charles Morgan wrote:
>
> At 11:20 PM 2/16/01 +1100, Roman wrote:
> >Just a quickie, has anyone connected a magnetic
> >coil pickup, as the typical sensor used in car
> >speedos, to a PIC??
>
> Roman, I needed to build my own Vehicle Speed Sensor for an engine swap.  I
> originally used a magnetic coil pickup driven by the speedometer cable.
> The coil fed a Harris HIP9020 "Programmable Quad Buffer with Pre and Post
> Scaler Dividers".  It's a zero-level detector and limiter made specifically
> for such applications.  I then used used a 16F873 to adjust the frequency
> to that required by the vehicle computer.  Unfortunately, the output of the
> coil is useless until a minimum speed is reached.  I replaced the coil
> pickup with a Hall sensor that I mounted in the differential cover and
> triggers whenever one of the ring gear teeth passes it.  The Hall Sensor
> feeds directly into the PIC.  It provides a usable signal down to about 0
> mph and is much cleaner.
>
> Charles Morgan
> P.S.  If you're stuck with the magnetic coil pickup and can't find a
> HIP9020, you can also use a National LM2907/2917 as a coil-to-PIC buffer.


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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