I bought a really neat wrought-iron door knocker. It's basically a little hammer, about 6" long, that comes down on a plate to make noise.
I'd like to convert this to a doorbell. Because the hammer is pretty heavy, I just don't think I can embed a regular switch in the plate. I'm thinking a hall sensor and a magnet.
I have 2 wires going to the doorbell, so whatever I do has to work off of 2 wires; if the arduino is at the doorbell then the two wires have to supply power as well as ring the bell, much in the same way as the existing lighted manual doorbell works.
(The light bulb in the doorbell is run in series with the solenoid coil. The bulb provides enough resistance so the solenoid does not activate. Pushing the doorbell shorts the bulb, and lets enough current flow to move the solenoid.)
The arduino would have to be powered in a similar way: a resistor to take place of the bulb, a relay across the resistor, a cap to store power while the resistor is shorted, and diodes to keep it all from shorting out. Plus some circuitry to provide 5VDC from the 16VAC the doorbell puts out....
Maybe. I assume the Hall effect sensor is on the inside of the door and the magnet is affixed to the knocker arm? Cheap parts, you need to prototype with door thickness... Different magnets have different flux patterns and your knocker will likely affect same.
Maybe a piezo used as a microphone fed to the Arduino? Then, this would also work for a knuckle-knock or police baton bang
I would go the a different way. Keep the Arduino near the power and bell. Use the cable to connect the sensor (whatever that is) to the Arduino input. Connect a logic level power fet to an Arduino output to activate the bell. You will need a small diode bridge rectifier (4xIN1004) and some smoothing caps to turn the 18VAC into something the Ardino can use.
All seems a little ott for a just a doorbell though! How about the arduino records time when the bell is rung (while you are out) and displays on an lcd?
All seems a little ott for a just a doorbell though! How about...
I thought the same. I'd probably opt for PIR and a video camera turned on by Arduino & ringing the doorbell & logging the event + duration, etc. Actually, I'm a recluse and just prefer folks stay away from my door and no-touchy the doorbell.
