Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

I noticed a post in the archives concerning the design of a infrared animal
detector. Someone had posted something about IR photodiodes. When one needs
to measure infrared radiation of objects close to ambient temperature, the
spectral response of economical semiconductor detectors really kills the S/N
ration. To detect animals you really need a long wave sensor, and the
photodiode style units can run a few hundred dollars.

A pyroelectirc detector for a dollar or two will work if you can chop the IR
signal, which is difficult to do in a handheld unit. Another possibility is
the thin film thermopile detector.

They tend to be more expensive $20-$100 in low quantities, all you need is
an op amp and a comparator to trigger an LED if an animal is within the
field of view. In volume they are pretty cheap as well as surplus when you
can find them.