At 11:21 AM 4/6/03 +1200, Jinx wrote:

>All circuits are in closed aluminium cases bolted to the plane's
>chassis and I recommended that grounded screened cable be
>used for signals (about 2m long) and power lines. The cable
>plugs into a 9 pin D. Portb4, like other inputs, already has pulldowns,
>ceramic caps, Zeners and Schottkys on it.

What value of series resistor between the pin and the outside world?  Do
you have a bypass cap right at that pin?

My input networks consist of the pull-up or pull-down resistor, then a 100K
series R (all of that physically close to where the signal enters the
enclosure) and 100n bypass cap right at the PIC.  If the input is coming
from a supply higher than Vdd, I also add a shunt resistor in parallel with
the bypass cap.

I use things like ceramic feed-through capacitors and series LC networks
only for gear that is going to live in strong RF environments (AM and FM
broadcast transmitter sites) - better safe than sorry.

Pretty much everything I make has to tolerate a 5W handy-talkie in close
proximity and the 100K/100n RC network I described above seems just fine
with that.

dwayne

--
Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

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