Ed Edmondson wrote:
> The window is now covered by light blocking double faced tape. The
> led is on solid. Putting my thumb on the tape causes it to appear to
> operate (led flashes without sync signal).

Lots of things that appear "light blocking" to us in the visible range are
surprisingly transparent at other wavelenths.  Black electrical tape is a
good example.  It attenuates visible light heavily (else it wouldn't look
black), but doesn't do much at all for IR.  I've had an opto interruptor not
react to three layers of business cards, which would have blocked just about
all visible light.

Try experiments by shutting off as much light as possible and put thick
solid objects on the PIC to see what happens.

I once had a 16C77-JW with intermittent problems on my bench.  After while I
noticed that it worked if I put my hand near it.  In the end it turned out
that my hand was attenuating the light coming from a window.


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