My first message to PICLIST, and it bounced it as a "dup'"... hmmm.
Well, I'll try again, as it doesn't seem like it could possibly be
a duplicate when I've never sent one before...


Greetings!

A few people have inquired about a source for light sensors which are
usable with PIC's.  I have done some work in this area, and have found
the TI "light-to-frequency" chips quite useful.  These 8-pin DIP's
output a variable pulse rate depending upon the light level they see.
It is a simple matter to connect their digital output to a PIC input
bit and measure the frequency of the pulse train, and hence the light
level.

Some models (like the TSL230, for example) are programmable.  This means
that their sensitivity and output pulse rate can be set by some digital
control lines.  If you use a few PIC outputs to control these lines,
you can obtain a very wide dynamic range of light measurement.

TI publication "Opto-Electronic Products, Product Summary" is a useful
starting point for anyone getting involved with these and other TI optical
devices.

For the person interested in sensing color of an object, I suggest using
multiple sensors with optical filters over them.  Check Edmund Scientific
as a source of colored filter material.  It would seem that "fuzzy logic"
techniques would lend themselves well to determination of "color" from
these multiple light-level signals.

Russ Reiss - HOPCO - russ.reiss@circellar.com
P.O. Box 2425, Vernon, CT  06066
FAX: 860-872-4681   BBS: 860-872-4684
PIC TOOLS: PICSPA Programmer, PICPRO Prototype Board, PICPGM Software
See June '94 Circuit Cellar INK, page 22.