I would like to integrate our conventional door bell into openHAB, to get a signal when the bell is rang and for example announce it via our Alexa devices.
The bell is driven by a 12V circuit. The challenge with it is that power supply, button and bell are in three different places, and neither where the button is nor where the bell is I have constant power to drive any smart devices. The bell only gets power if it is rang, and at the button I only have the one switched wire:
Only at the power supply I have power, but not sure if I can connect a smart device there to get triggered when the circuit is closed. I’d prefer to work with Shelly components, such as the Shelly Uni or Shelly Plus 1, since I already use a couple of those. Could either of those be used to get an indication at the power supply if the circuit is closed?
If there is no solution with Shelly components, of course any other solution that integrates with openHAB would be fine too.
One way to do this is with Zwave at the bell. Get a small 12V relay, and use a Zwave door window sensor that has a dry contact input. When the button is pushed there will be 12V across the bell which will trigger the relay. I have Ecolink sensors that work for this, but I don’t see the dry contact mentioned in the manual. Not sure if this has been removed.
I don’t know if there is a clever current sensing device you can put at the power supply that can drive your Shelly. Current is flowing when the bell is pushed and I’m sure it is measurable, but you probably want an easy way to measure it, not a hobbyist project. The voltage from the power supply probably also droops a bit, and I suspect you could measure that too. Perhaps a bit less reliable, but it might work.
Presumably there’s an internal pull-up resistor in I3, but when the button is pressed, the small current will flow through the bell’s relatively low resistance down to gnd. I doubt if that’ll be enough current or voltage to drive the bell. The pull-up resistor would be in the range of 1k or probably much higher.
If this Shelly also has an output then the bell could be hooked up to that instead, but that would require some additional rewiring in which case you might as well connect the Shelly’s input to the button instead, and not disturb the existing bell circuit.
correct. At least this solution provides a way to integrate the switch without rewiring. For sound output there are many options. I use an Android tablet running MainUI within habpanel (but should work without habpanel now - haven‘t had time to test it)
Connect bell to both input and output. Keep output normally off.
When button is pressed, whether Shelly can sense it (whether there’s enough current to bring it down to low). Shelly has to detect the leading edge of the trigger (when button is pressed, not released)
Then program Shelly to momentarily (2s or however long to let the bell sound) turn on the output to power the bell (the button must also remain pressed). But after 2s or so, switch off the output to resume sensing future presses of the button.
Maybe 1s is enough. Most people don’t hold the button down that long
Probably the cleanest solution is, like what @rlkoshak said: remove the bell, just bypass / connect its two terminals, replace the button with Ring (or similar) and install the chime for Ring which works off some sort of wireless link.
Our bell works at 12 - 13 V ac (germany), and i’ll use this bridge rectifier . DC output signal controls a photo coupler via 10 kohm resistor. Second circuit of photo coupler is linked to a pio of the raspberry input. ( using pigpio binding). You could also use a fibaro smart implant (zwave) , if you don‘t like the pigpio version, or a D1 mini (flashed with tasmota) , all in a small box , close to the bell.
As I am still waiting for the bridge rectifier, this is still theory.