> I agree Latchup looks like the most likely culprit, but how it's
> happening is what I thought may be a little different.
> I noted Joe said he tried an opto-isolator, which should provide pretty
> good protection on the pin. If a "direct" path, I thought it more likely
> the power supply may be getting corrupted (i.e. if the HV and PIC
> circuits are sharing power+ground)
> If this is the case a DC to DC could be used between the two sections
> (looks like it's all powered by the battery from the circuit posted)

Temporary operation form a local battery can be useful when
troubleshooting this sort of thing.

Location of battery and what is left connected may help in cause localisati=
on.

eg best results probably achieved by a battery connected wt short
leads to processor supply and with usual power circuitry diconnected
near connection to cpu (subject to power continuity leads for other
parts.

Worst case improvement may be to use battery connected to regulator
used to provide cpu . (This allow maximum induction into circuitry,
glitches on rail preregulator etc.

Common sense and careful thinking required.


 R
--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.