> I have a PIC 18F1320, 2 pressure sensors, a LM335, a MAX232, LCD display
> (no backlight) and fiber optic receiver & transmitter. The sensors are
> remote mounted, everything else in a 4" x 4" x 2" cast aluminum box. The
> 12 VDC power comes from an external wall wart. The LM7805 regulator gets
> hot to the touch without a heat sink. The 12 VDC in measures at 61ma.
> add another 10 ma. for the LCD display. The ambient in the area can get
> to 120F or so.
>
> I'm assuming I need a heat sink, probably prefer a heat sink on the
> board, but could screw the grounded tab of the 7805 directly to the
> aluminum box.
>
> Thoughts?

At half a watt or so at 120F ambient, you are probably quite safe without
a heatsink, however you may find your measurements more accurate if you
moderate the temperature near the analog parts(that includes your PIC). In
that case, a heat sink will not improve things. Attaching the regulator to
the aluminum case will help.

Cheerful regards,

Bob


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