frequency to voltage conversion.

[Dirk Broer]

>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?

Your best bet for accuracy is a frequency counter - this would also tend to 
eliminate noise (a digital filter if you will).

Suppose you find out the MAP sensor outputs between 50-150 HZ depending
on pressure.  Hook up an 8-bit counter and read it every 10Hz.  You'll expect 
readings between 5-15 counts - this is a little low on accuracy but allows for 
rapidly changing pressure levels.  On the flip side, if you read once a second 
you may end up with 50 to 150 counts but a rapid change would not be noticed - 
or rather it would be averaged in.  Every time you latch the current count you 
clear the counter.

Dirk