>Charles wrote:
>Just doing a little thinking here and I was wondering what my options
>are to protect circuitry from the elements.  I was thinking of encassing
>the whole controller (PIC, crystal, regulator, adc, etc..) in epoxy to
>protect it from rain, snow, etc...
>

I have had some experience in potting small high voltage power supplies.
The use of hard epoxy is not recommended - it can break components by
differential thermal expansion. Flexible epoxies made for circuit potting
(such as from Conap and others) are OK. We used to test power supplies for
thermal stress cracking by letting them sit in boiling water and then
dropping them in ice water, repeating this several times.
Dow Corning 2-part RTV silicones (catalyst types) work well but are expensive.
One of the best things for potting is beeswax - it is used to pot several
commercial sonar depth sounders for boats. I believe it is even more
impervious to water than epoxy and can be melted out for circuit repair.
However, the use of beeswax potting on line-powered circuits presents a
serious fire hazzard.
In general component overheating is not a problem for low-powered circuits
since most potting materials have thermal conductivities greater than air.
The exceptions are components using a heatsink and relying on air
convection for cooling or components running at a high temperature, such as
power resistors.

Maris