Open, Sesame – entry phone hack

I still have an annoying analog entry phone in my flat. It does not have the numeric keypad to type the passcode and enter the staircase. I am too lazy to open the block door with a key every time I come back home, but this can be solved easily. Of course I did not mean the replacement of the entry phone with a new, digital one – that would be too easy and too obvious. Here’s my quick weekend project – analog entry phone hack, which opens the door after ringing in the secret passcode consisting of short and long rings. Traditionally, I have added some useless functionality like PCM audio playback from the SD card to make it more fun. It can play some samples, e.g. from retro games, an Arnie movie quote or… a barking dog when the guest or postman calls.

The circuit is installed in the handset. It detects the call signal and simulates the button press with a relay switch if signal matches the programmed pattern. It is also connected to the microphone output and can play the audio files on guest call or passcode input. I have built this circuit in an hour using components I had around – ATMega328P microcontroller, universal soldering board, relay, 3,3V LDO regulator and some passives.

You can download the source code and schematic below. The whole project was made in a couple of hours, so the sources looks a little messy. The circuit does not provide proper isolation from the entry phone circuit, so if you are going to built it yourself, you might want to add some optoisolators.

  Pobierz plik: entry_phone_hack_0.1.zip
  Rozmiar: 1.07 MB
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