My sneaky cat can open all doors of the apartment, even the fridge door. No meat is safe any more.
To prevent that I built a cat repeller using an Atmel ATmega328P Arduino Nano 3.0 board:
- a HC-SR501 PIR motion detector first checks if the cat is nearby (or any other movement happened)
- then an E18-D80NK IR range detector verifies if the cat is in front of the fridge (it's pawn is present at the corner of the fridge's door)
- if this is the case 24-25 kHz PWM signals will generate an ultrasound using a piezoelectric diaphragm, encouraging the cat to leave the premisses
- if it still opens the fridge, a switch is released, and a human audible alarm will sound until it is closed
The firmware is available on git, with connection information.
The device is placed in front of the fridge and is battery powered using 3xAAA batteries and a 5V boots regulator. This last only around two days before the batteries need to be recharged.
Why does a 24-25 kHz sound annoy the cat? There is no psych-acoustic secret behind it. It's just a loud ultra-sound (> 20 kHz) in a range the cat can hear, but not humans can't. Else it would annoy us too.
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| PIR motion detector | IR range sensor | piezoelectric element |
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| all elements connected | final installation |