Roman:
I haven't tried it but you may be able to rework a board for something
like this:

                                +5V
                                |
                                /
                                \
                                /
                                \
                                /
                                +------------ To PIC input
                                |
                               /
                             |/
 _________||____/\/\/\_______|    2N3904
(         ||            _|_  |\
( coil                  /_\  | V
(                        |       \
(_________||_____________|_______|
          ||                     |
                                 V


-- Rich


Roman Black wrote:
>
> 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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