Using a Door Handle Conductivity to Detect Intruders

Sometimes the simplest projects can be quite interesting, provided they’re well documented. We hope that the Hackaday readers also think that the door sensor that [Alexander] developed falls into this category. Instead of using common methods such as a magnet + reed switch, he decided to use the strike plate and door conductivity to detect someone walking in. The setup he put together includes an Arduino, a PowerSwitch Tail (a power cord that switches 120vac with a dc control voltage of 3-12vdc), a battery pack made of 8 AA batteries and two crocodile clips for door connections.

Most new hobbyists would have stopped there, but [Alexander] checked his platform’s power consumption and continued his work to decrease it. He therefore put the microcontroller in power-down mode by default and uses an AVR external interrupt to wake it up. In case beginners can’t understand [Alexander]’s code, he actually put a nice flow diagram on his website. Embedded after the break is a video of the system working.

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