I currently own a Nest doorbell that uses a "chime connector" between the doorbell wires and doorbell chime as shown below.


I have tried to create a digital doorbell chime that will wirelessly connect to another device to notify me of visitors. I tried using this schematic for my doorbell but after a month of use, the solid state relay in the chime connector would not release and it would stay "closed," causing the doorbell to turn off because all the current was going through my chime design instead of through the Nest doorbell.


Forum posts describing the inside of the chime connector show that it uses a solid state relay which I presume is controlled by a triac. My guess for why my design would not allow the doorbell to "stop ringing" would be because there is no zero-crossing point for the triac when it's outputs is two diodes, causing it to conduct forever. Would using a single diode and a voltage divider work better in this situation than an optocoupler for detecting doorbell presses from a microcontroller? How can I fix my design so the solid state relay in the chime module stops conducting?

  • \$\begingroup\$ The purpose of the chime connector seems to be to short-circuit the chime to allow the nest hello to draw more power from the bell circuit. I don't know what signal is needed to cause the chime connector to open. \$\endgroup\$ – Jasen Apr 28 '19 at 3:05
  • \$\begingroup\$ In your picture what is "doorbell" is that "Nest hello" or something different? \$\endgroup\$ – Jasen Apr 28 '19 at 3:06
  • \$\begingroup\$ @Jasen Yes, it is the Nest Hello. And no signal is needed to 'open' the chime module from the chime side of it, but something I'm doing is causing it to stay closed. \$\endgroup\$ – dylanweber Apr 28 '19 at 3:07
  • \$\begingroup\$ Yes, the nest hello should be sending the correct signal, it could be that your load passes too little current, maybe add 33 ohms (or an actual chime mechanism) in parallel with the opto-resistor pair. A real chime solenoid looks like a variable inductor, starting low and increasing in inductance as the armature moves \$\endgroup\$ – Jasen Apr 28 '19 at 3:20
  • \$\begingroup\$ @Jasen I don't think I want to send 720 mA through a pair of LEDs only designed for 60 mA. Should I add a small value in parallel? I tried adding 500 ohms in parallel to the "output1" and "output2" lines but it made no difference. \$\endgroup\$ – dylanweber Apr 28 '19 at 3:44

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