In article , Pat Ziegler wrote:
Looking to build a simple circuit that will fire a relay if an insect gets
across the input terminals. I'm thinking a simple Op Amp Comparator would
work.. The end result is to release the shutter on a 35mm canera. Need to
keep the camera from taking to many pictures so a delay between shutter
releases would be a plus...

You're asking a lot. Insect exoskelatons don't conduct real well, and if you
up the voltage I doubt the insect would respond well.

You may have to go with some form of optical motion detector.
(PIR is no good insects are cold blooded,
"Radar" (microwave) is no good insects are too small)

Something with two sensors near the centre of the image
(attached somehow to the viewfinder?) that compares their
output and triggers on sudden changes might be the go.

otoh a sensitive pressure pad could possibly be built using aluminium foil,
it'd miss small ants, but medium sized cockroaches would probably set it off.
if you use gold leaf instead it could be made more sensitive.

Bye.
Jasen