Doorbell - need help

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  • Hi, I want to play around with my doorbell now and don't really know where to start.

    Using off the shelf wireless doorbell is not an option as the installation is already there. So I'm stuck with these thick wires - one goes to a button, one goes to the sounder and the third one (I guess?) is a power source. I got them all meeting in one box so I can put Espruino there :) Espruino will have external USB power adapter.

    Ideally I would like to be able to setWatch on the button and then Pin.write to the sounder. Programming is not an issue, but cabling is - don't want to burn the house down.

    To get the signal out of Espruino I was thinking I could use a relay module. How about getting the signal into the board? Any suggestions?

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  • @Rollo I it looks like your assuming these cables are carrying 230v AC?
    So please proceed with Caution as It can kill if not used safely!!

    The first step is see if the bell system is using 230v.
    Can you see and take pic of the bell sounder unit?

    If not do you have a multi meter?
    If so could you measure the voltage between the 2 joined Brown (Live) and 2 joined Blue (Neutral) . You will need to put your probe into the remaining hole in the connector (orange & transparent thing) .

    If the system is using 230v they you need a interposing relay one who's coil is 230v/ac that would connect to the button cable & neutral and it's volt free contacts can drive the digital input on Pico.

  • As @LawrenceGrif says, I guess the best bet is to figure out if the doorbell is using mains voltage first... And also if it's AC voltage or not.

    If it isn't mains

    Then everything's easy. You may still want to use a relay module to drive the doorbell (if the voltage is DC then you could use a FET, as it'll be a lot smaller).

    To get a signal into Espruino you might be able to use a few resistors as a potential divider to convert the higher voltage down to 3.3v, however an easy and very safe way to do it would be to use an optocoupler/optoisolator. I'll post up more info if it turns out you can use this, but it's basically a light and a light sensor in a small package. You connect the light up to the alarm's power, and the sensor up to Espruino. That way there's no electrical connection between the two systems, but you can still tell when the alarm is pressed.

    You might also be able to power Espruino straight from the door bell's power supply...

    If it is mains voltage

    You'd need the relay module, or an SSR (solid state relay - you might be able to find a smaller one of those).

    But to sense the door bell button being pressed, you could make yourself an optoisolator... Get a small light that can be powered from the mains (maybe a neon bulb?), put a light sensor like an LDR or photodiode next to it, and tape them both together so no light can get in. It'll be a nice, safe, easy way of sensing mains voltages :)

    Also you probably want to stick a capacitor across the light sensor - because the mains is AC the voltage would be going up and down 50-60 times a second (and the light level at twice that). If you add the capacitor you can smooth all that out and can then do a simple setWatch like you wanted :)

  • Yes it's AC ~230 mains installation. I'll shop around and see what I can find, can't wait to get it working :)

    Thank you both.

  • Just checked, and you can get smaller SSRs - you could get just the SSR itself too, as it looks like you don't need any special circuitry.

    Another option for sensing is to use a relay with a coil that can be powered from mains, and to then connect the Espruino to the contacts on it....

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Doorbell - need help

Posted by Avatar for Rollo @Rollo