Electronic Mouse Trap

This electronic mousetrap uses a PIR motion sensor to release a door when a mouse or rat enters the trap. The PIR was removed from its case and the sensor peeks through a hole in an aluminum-clad board. It turns out that a rat will gnaw right through the plastic of a typical PIR sensor, if given enough time! The audio beeping from the sensor triggers a two-FET circuit that momentarily closes a relay, operating a motor that pulls a pin, releasing the door. A homemade latch is visible on the left and it was enhanced by the addition of a cabinet latch. They now work together to keep the door tight against the hole. A piece of poster board shields the PIR sensor from the intruder until he gets deep inside the trap. Otherwise, the long tail on a large rat will still be sticking out of the door, letting him escape. Another piece of white poster board along the back keeps IR reflections from triggering the detector early. The box is a plastic terrarium with the screen shield and door replaced with a thick piece of plywood, with an appropriate dado to let it slide into place.

A piece of nylon lacing cord is used to pull the pin holding the door. The cord is secured to the motor shaft by jamming a plastic roller over the string and shaft, pinching the string against the shaft. This is a neat way to make a linear servo with lots of pulling power. The pin is positioned by hand to reset the trap. I leave a little slack in the string so that the motor gets up a little momentum before it tries to pull the pin. Gravity slams the door.


Put the bait off to the right so the little fellow gets all the way inside the trap. The PIR sensor is lined up with the little hole in the aluminum plate. He won't gnaw through that!

Here's the Results Video Look closely and you can see the plastic parts he chewed off the PIR detector.

Ideas from this Project