When I was a kid thumbing an ancient issue of Popular Mechanics Magazine I encountered a morbid high-speed photo of a mouse execution. The luckless mouse was airborn as the bar of the mousetrap closed in for the kill. I think that's when the obsession took root. In college I made my first camera trap under the guidance of the late Professor Joe Hall of San Francisco State University. That was the "doorbell model". The trigger--a whisker switch--was wired to a battery-operated doorbell. Activating the switch made a little wooden bar press the shutter button. At the time, it was a wonderful gadget, but you had to hand crank the film after each exposure. If you were lucky you got one picture a night.
In 1980 a couple of my colleagues from the National Zoo and I went to Indonesia where we used an improved homemade camera trap to photograph the little known Sulawesi civet. Camera technology was becoming electronic. We wired a photoelectric trigger to plug directly into the electrical shutter outlet on the front of the camera--a Nikon FE. With battery powered film advance, you could take many pictures in a night. Two months later we were back in the states impatiently waiting for our developed film. When it finally arrived, we found that box after box had slides of night-flying moths and falling leaves. But there were also a few photos of the civet, and we considered it a great success.
Now in the age of the "home-brew scouting camera" you can get hundreds of digital pictures a day. I have slowly advanced from easy-to-build "plug and play" systems, to those that require taking the camera apart and soldering internal contacts. Luckily there are some great support groups on the web, whose mentors patiently assist greenhorns.
Affordable digital cams have one irritating deficiency--the camera has to be turned on to take the first picture when an animal activates the passive infra-red sensor. The delay of a few seconds can give you a lot of cut-off images.
The latest control boards however keep the camera awake when there is infra-red activity, which means you no longer have to wait for the camera to wake up for each picture. This is an acceptable challenge. You just have to use your "jungle lore" to compensate for the camera's shortcoming.