MQTT and three way switches

Question

Hello, I am developing a lighting service for my home. I am using raspberry3 + 8 channel relay card + mqtt, everything works fine but I would like to add three way switches. My question is how to update the status of lights in mqtt if this is triggered by the switch?

andrequeiroz.com · Accepted Answer

Good idea ravi, would you have to use multiple digital input on a port? because the relay card has 16 channels, and if you use a digital input by gpio I think that gpio is missing.

ravi_butani · Answer

instead of using mechanical switch to control the load directly, use it as a digital input of control system (Pi) than you can read the status as well

jw0752 · Answer

Hi Andre, Can you monitor the voltage at the light itself? John

jw0752 · Answer

Hi Andre,

I would need to know more about your system and the voltages involved to give you a correct answer. The three way light switch setup gives you off and on control of a light from two positions but the light itself remains binary. It is either on or off. I am not familiar with how the mqtt senses but there is certainly a way for us to interface it to the light. Is the mqtt for this circuit currently sensing a voltage? Is it the same voltage as the light? Draw a schematic of your circuit for this light and if I can't give you a definitive answer someone else will be able to.

If you are putting the 3 way switching in the software of the Raspberry so the you continue to use the same relay for the light and just use the second (3way) switch location to tell the RP the position of that switch then I would suspect that your current mqtt sensing would remain unchanged.

If you are putting the 2nd (3way) switch in the light circuit then also be aware that the relay on your relay board will need to have a SPDT set of contacts.

John

clem57 · Answer

Take a look at https://www.youtube.com/watch?v=GEJCk-Dr3BQ . They talk about many thing including 3 way switch.

andrequeiroz.com · Answer

I think that would not be the best solution. because the costs are high and would have many devices connected to wifi.

I was thinking of a board with addressable channels. this would be linked to the switches and the raspberry.