FW: Frequency to Voltage Conversion: how?

[Ciciora Steve]

  Someone writes:

MAP and BP sensors apparently do not return voltage as output.  Instead
the oscillate at a frequency which corresponds to the absolute pressure.
What electronics are involved with frequency to voltage conversion?

This brings up another point: what output frequency corresponds to what
pressure level?  I'm sure we could test one to find out, but isn't there
already some book or manual that gives in depth data on sensor readings?
If we have to test every sensor, it is going to take a LONG time.  Surely
Ford, Chevy, and/or Bosch, publishes a manual for servicing EFI that
describes how each particular type of sensor responds.

  Most single chip computers can measure frequency much better than voltage,
which is why MAF sensors output frequency.  Since I don't know the frequency
range for this sensor, I can't comment on the best circut to do a freq. to
voltage conversion.
  My GM map sensor outputs a voltage proportional to the pressure *and
reference voltage*.  I did a pressure calibration and found it to be extreemly
linear and very dependent on ref. voltage.  Three terminals: ground, ref in,
and output voltage.  I gave mine 5.0 volts.  I don't have the data handy, but
can post if you would wish.  I plan on calibrating all that I own to find out
repeatability info.  The MAP sensor I use is used in my '89 Berettas (4 and 6
cyl), my sister's '89 Corsica, and my friend's Jeep.
  - Steven ciciora