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Sonoff with 2-way Physical switches

Hello, I have a scenario in which I have 2 physical switches to control a light and I want to connect it with my sonoff 4ch pro r2. I was thinking of connecting one of these physical switches to sonoff so that I can control the light using the physical switches and eWelink. Can anyone provide me a connection diagram for this scenario? I understand that the live status of the switch won't be updated properly if we combine it with physical switches. I'm okay with with that.
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You could install a crossover switch (the middle one) and then use one channel of the pro as one of the end switches.  Or you could use two channels of the pro in interlock mode to function as the crossover switch.

Replacing the center crossover switch with two channels of the pro would look like this:

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If you just want to replace one of the existing switches with the pro then the diagram below applies.

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In this case on one channel of the pro the common would be say for the left switch the "hot" wire with the NO and NC connected to the other two wires.  Replacing the right switch the common would go to the bulb center pin with the NO and NC connecting to the other two wires.


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If I'm going with the second case, then both the switches should be on to power on the light. Isn't it?

Not sure what you mean by "on" with a 3 way switch.  The common always connects to one contact or the other.  In the case of a relay when it isn't energized the NC is connected to the common and when energized the NO is to the common.

I just tried the first option using interlock with my 4ch pro and the physical switches are not always properly turning on and off the light
For trying out the second scenario, would you mind explaining what how to do connect my 4ch with it? I'm finding it hard to understand

Image result for 3way switch

To replace the left switch with one channel of the pro.  The hot wire goes to the common on the relay.  The top red wire connects to the NC.  The bottom black wire goes to the NO.


With this connection current flows exactly like the diagram when the right switch common is connected to the top red wire.   Energizing the relay OR switching the physical switch will turn off the light.

This second circuit also doesn't seems to be working for me.. I was looking for a solution to turn on or off the light using either of my 2 physical switches or eWelink.

All I can do is provide the diagrams.  If you have two existing 3-way switches and wish to keep both of them then use the diagram above to add a 4-way crossover switch between them using two channels of the Sonoff in interlock mode.  It will work if you wire it correctly.

Thanks a lot man. I'll try with the that circuit again with a lhysical crossover switch and then once I get it working, I'll try to remove the crossover switch and try 4ch pro interlocking crossover.
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Perfect.. I'll try it out and post here. Thanks a lot for your help big help E W.

Keep in mind that the Sonoff requires an always hot wire and a neutral to power it.  It cannot be powered from either of the two "traveler" wires.  One of the two channels used has to be energized at all times.  Having both channels d-energized will not work.  For example if you use channel 1 and 2 then you only switch on ch 1 or 2 in the app with ch 3 and 4 never turned on. 

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Thx a ton. I'll try it out tomorrow and let you know my output
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