About 4 years ago one of my students managed to get a sensor donated (cosmetic defect) that I believe was a very large area brown colored chip. Chip was about 1/2 inch square mounted in a round package about 3/4 inch round with a top that was optically clear. This thing had just two wires. I designed a simple op-amp circuit that would respond only to changes in output. I used a current to voltage coverter at the front end to get maximum sensitivity. This thing was quite amazing. It was extremely sensitive to the radiation emitted by humans. What I found interesting was that it had no trouble at all detecting a human through several layers of clothing, including heavy winter coats. It did not seem to be "infra-red" detecting in the sense that we normally use that word. It was sort of tuned to the specific heat signature of the human body. It could even detect this heat signature when the detector was covered with a sheet of aluminum foil. In fact, one of our major problems was preventing it from picking up signals that were coming in from the sides (and even the BACK!). But it ignored squirrels. (Never tried it on a cat). I don't think it was the fur that prevented detection, because we had one person acting as our target who had TWO very thick coats on, gloves, and two hats facing with their back to the sensor, and they were easily detected. Unfortunately I can't seem to find the project report in any of my filing cabinets at the moment, but I vividly remember how it could detect humans with great ease. It could be that the detector being touted by this company actually responds to the specific human body signature, just like the sensor in our project. Fr. Tom McGahee ----- Original Message ----- From: Sean H. Breheny To: Sent: Tuesday, February 27, 2001 3:40 PM Subject: Re: [EE]: Infrared Detector vs Pet > Hi Scott, > > Perhaps you are right, maybe the outer layer of fur is cool and obscures > the inner layer. Also, I realized that my idea is a little messed up (you > don't want a dead zone), and I don't have time at the moment to figure out > if there is an optically feasible means to reject small objects :-) > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics