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Circuit Notebook

Interesting circuit ideas which we have checked but not built and tested. Contributions will be paid for at standard rates. All submissions should include full name, address & phone number.

PICAXE-based mouse trap is non-lethal

Click for larger image

This mouse trap uses an IR LED and phototransistor coupled with a PICAXE08M microcontroller to operate a small motor that closes a trap door. This design avoids the main problems with traditional spring-based traps, in that they are difficult to set and often fingers are caught during setting up. Secondly, the sneaky mice often eat the bait without setting off the trap.

This humane trap is constructed from two short lengths of 25mm PVC pipe, with a right angle elbow in the middle and a snug-fit removable cap at one end. The bait (usually chocolate) is placed at the cap end. About one centimetre from the other end of the pipe assembly is a slot for the trap door that is cut half way through the pipe.

The trap door is cut out of some sheet metal to fit the internal curve of the pipe and arranged so that it can pivot into the pipe and seal the exit. A 2mm diameter hole in the door and a pin in the shape of a threaded eyelet is inserted to keep it open. The pin is connected to the shaft of the motor via a short cord.

When the trap is triggered, the motor is energised for a short time,
wrapping the cord around the shaft and pulling the trap door pin out to release the door, with gravity closing it.

Click for larger image

The mouse detection circuit is located at the bait end of the trap and comprises an IR LED opposite an IR phototransistor. When the mouse breaks the beam, the trap door is closed.

The IR LED and phototransistor were sourced from an old disk drive. Similar photo-interrupter components can be found in printers and can be separated easily to be placed apart so that the mouse can interrupt the IR beam.

At power on, a short tune is played and a red LED is flashed. After this sequence, the red LED flashes to indicate normal operation. The IR LED is also pulsed briefly at the same time, to prolong battery life. When the IR beam is broken, the motor is energised for a short duration to close the trap and the tune “Silent Night” is played to notify successful operation. The tune is repeated at 15 minute intervals.

The captured mouse is not harmed and can be released by removing the snug fit end cap. The trap could be adapted for other animals by suitably scaling up of the pipe and other components. Power comes from three 1.5V alkaline AA batteries.

The software, MoustrapV4.bas, is available for download from the SILICON CHIP website.

Phillip Webb,

Hope Valley, SA. ($60)

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