Sorry, I just sent this note to just Paul...

>D. L. Davis wrote:
[snip]
>>
>> Everything works great with one big exception.... the PIC is extraordinarily
>> sensitive to light!
[snip]
>
>This doesn't surprise me at all.  Silicon is photoconductive, regardless
>of whether you are talking about junctions or MOS capacitors (i.e.,
>gates).  The degree to which a given function is affected by light would
>depend on several factors:
[snip]
>1. Metallization: the Al layer is opaque.
>2. Impedance: lower impedance circuits are less affected by leakage
>3. Location: circuits nearer the center of the die have a wider field of
>view
>
>Whether the A/D is the charge balancing type, current sources, or
>resistor ladders, it's bound to have some relatively high impedance
>sections.
[snip]
>Paul Mathews, consulting engineer
>AEngineering Co.
>optoeng@whidbey.com
>non-contact sensing and optoelectronics specialists

Does this mean that the PIC (I presume 16C7x) could be used as a light
meter?  ie put on a constant voltage (ie from a voltage divider), leave the
window open and output what the ambient light is?

What frequencies would this be best for?  I presume you would want to put in
a ultra-violet filter (any ideas of what to use)?

myke

Today, the commercial sector is advancing computer and communication
technology at a breakneck pace.  In 1992, optical fiber was being installed
within the continental U.S. at rates approaching the speed of sound (if
computed as total miles of fiber divided by the number of seconds in the year).

Aviation Week and Space Technology, October 28, 1996