3 Way Switch with Relay Sensor

  • I would like to use a Relay Switch to turn some lights on and off, but I would like to install them in such a way that the existing light switches would still work to turn the lights on and off manually. I wanted to integrate the Relay as a "3 Way Switch" using a traveler wire, so I can turn the lights manually and turn it off with the relay and vice versa, but wasn't sure if the Relay can do that.

    Has anybody here tried something like this? If so how did you integrate the Relay into your system?

    I usually only use 2 of the 3 pins available in the relay, and I was wondering what the third pin is for. Is the third one where I would connect the traveler wire?


  • Hero Member

    What do you want exactly?
    Can you fill in the question marks below or make some other kind of truth table?

    Manual switch On, Control On ==> Lamp ?
    Manual switch On, Control Off ==> Lamp ?
    Manual switch Off, Control On ==> Lamp ?
    Manual switch Off, Control Off ==> Lamp ?

  • @daulagari

    This is what I want. One of the switches bellow is a regular light switch, and the other one would be a relay controlled by my Vera.


    So, filling out your truth table:

    Manual switch On, Control On ==> Lamp ON
    Manual switch On, Control Off ==> Lamp OFF
    Manual switch Off, Control On ==> Lamp OFF
    Manual switch Off, Control Off ==> Lamp ON

    Notice that no matter what the combination is, once you flip one of them, the lights will change the state.

    I understand the concept, just don't know how to wire the Relay in this situation.


  • This is not a very easy thing to accomplish. You COULD wire the relay to replace one of the 3 way switches but the controller would not be able to tell what the state is of the other switch (or the light), just what the state of the relay is. The 3 terminals on the relay correspond to the 3 terminals on a 3 way switch. They are labeled Common, NC (normally closed) & NO (normally open). The Common would correspond to the terminal the hot or light is connected to (depending on which one you replace) and the other 2 would be the "travelers". However, any 3 way home automation switch has you replace BOTH switches, one with a master and one with a slave. The master is the one that actually controls the state of the light and the slave lets the master know to change state.

  • @Paul-Augusto

    Thank you for the reply! My Relay does not have the labels you mentioned above, that's why I was confused. But I figured out that if I connect the Hot wire in the middle pin it will switch between the other 2, so that was helpful and is exactly what I needed I guess.

    You are correct about not being able to tell the state of the light, I didn't think about this. Maybe if I connect a light sensor to my Arduino I could send back the state to Vera based on what the sensor tells me instead of the state of the relay? I'm just not sure if this would work during the day when the windows are open, the sensor might think the lights are on if there is enough sun light in the room.

    Anyways, thanks for the help. I'll keep playing with this and see what I can come up with.

  • One of the AC current sensors might work to tell you when the light was engaged by one of the other switches? though I have not tried any of them.

  • Hero Member

    I know what you are trying to do, but in some cases a MySensors solution is not an efficient solution. I would just buy a 3 way z-wave light set to meet the goal.

  • Hero Member

    Just wondering: Why would a 3 way z-wave light set work here better?
    How is it different from a 3 way relay?

  • Hero Member

    If I've understood your requirements/goals correctly, which looking back I may not have.. :-), my initial knee jerk response was based on these 2 thoughts.

    1. Incomplete state feedback to Vera
    2. Solution size (fitting it inside a switch box)
    3. Possible added wiring needs.

    I think these challenges could be solved with a cheap GE 3Way switch kit. If you're looking for a MySensors solution, with full implementation, I think @marceltrapman is working on a possible solution for such a problem.

  • Use a latching relay. Here is one I found on Amazon. https://www.amazon.com/dp/B015MRQNXS/?coliid=I3LXTGKX4GEPUR&colid=31WWM91JAUE22&psc=1&ref_=lv_ov_lig_dp_it

    If you are trying to use with existing 3 ways use https://www.amazon.com/dp/B015MSYQ8Q/?coliid=I3RP8X9OMYWU97&colid=31WWM91JAUE22&psc=1&ref_=lv_ov_lig_dp_it

    Use an optocoupler to indicate lamp status...see the last diagram in this post. https://forum.arduino.cc/index.php?topic=435506.0

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