Quentin wrote

> This is what I do in the lab as well. Problem is, most of my PIC apps.
> go into the industrial environment where there is AC lines, switching
> relays and contactors, AC and DC motors and whot not. I've got a
> standard filter for my digital I/O (Series R, 5V Zener, cap, Pullup R)
> and it works fine. Now I want to get a standard filter for the A/D to
> keep all these nasties out.
>

This is a big topic......
I was horrified at the energy of "noise" induced in wires in an
industrial environment, so bad was it I used to look at leds flashing
randomly when all they were connected to was the wires coming
from roller gate limit switches.
If you are trying to filter in an environment as nasty as this, forget
it..... isolate instead.
My approach would be to read the the analog voltage right at the
sensor, with its own isolated power, A2D it and send the data back
by some appropriate means, optical cable would be best( I have
some fine results from plastic cable and screw clamp emitters and
receivers) but a twisted pair RS485 could be used with appropriate
driving, terminating etc.

Brilliant application for a 12C672... as a remote A2D, you can
customise every part part of design, especially the transfer protocol.

_____________________________

Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand

www.psych.auckland.ac.nz

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