At 07:48 AM 4/16/03 -0400, Olin Lathrop wrote: >Photocells convert light to electrical energy, and don't operate on >varying resistance. The problem is that the term "photocell" refers to at least 3 different sensors, each with radically different characteristics. These are: Light Dependent Resistors (LDRs), solar cells, vacuum tube photocell. (side note: The last time I saw one of those vacuum tube photocells when I was a teenager - I do remember that it wasn't a photo-multiplier - the tube had 2 elements within: curved plate and a vertical rod up the center. It was so long ago that I can't remember if the curved plate was anode or cathode.) Anyways, what Olin is referring to could be either photo-diodes or solar cells. However, other types of photocell (CdS) *do* change resistance with changes in light level. Also note that a photo-transistor can give the illusion of a resistance changing value in response to changes in illumination. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 19 years of Engineering Innovation (1984 - 2003) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu