On Wed, 23 Sep 1998, Rivoir Robert wrote:

> I seek a simple means to measure  20 Volt DC with a PIC 16C84.  8 bits
> resolution suffices.
--SNIP--
> Would someone have a schema using a NE555 (or other small IC) in
> voltage/frequency converter whose PIC could have measure the period ?

Take a look at

http://www.bobblick.com/bob/stamp/555a_d.html

for a simple 555 setup. You can't measure down to 0V with it, though, but
you might consider another Op-Amp stage which adds, say, 5V to your input
voltage and then gives it to the 555 (it's a good idea to buffer the
input anyway). On the other hand you might run into troubles with
accuracy then.

Why don't you use a cheap A/D converter like the ZN449? I got some
recently for as cheap as 0.95DM here. If that's too many pins (18), use a
shift register with parallel load to serialize the data.

Georg.