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By Marko Mocilac
#90226 Hi,

One of the projects on my list is to build switch using ESP8266 and relay board for switching AC current load.
That part seems to be pretty much straight forward.
But I wouldn't stop just there.
Beside having a wireless switch option, I would also like to have another manual switch. I would like to control same load by using manual switch and this wireless switch.
Basically I want to achieve 3 way switch (or in Europe it is called 2 way switch) like the picture below shows.


To do that properly, I would like that my ESP8266 is aware of the status of the load (is it for example light turned on/off).
Therefore, I thought that I need some kind of circuit that can sense load status and get feedback in terms of logical level voltage to ESP8266.

The reason for this post is to see what options are available. How to achieve that ESP8266 gets feedback of the load. My attempt would be to make this as smaller as possible so I could possible fit it into the current wall installation.

One of the options is to sense current using Hall Effect current sensor which uses current transformer and operational amp to produce logic level.
Does any one have experience of designing and building such circuit on it's own?
I can buy final product, but I would like to learn something here so I would appreciate if someone could help me. Besides that, I am trying to keep design smaller. One ESP8266 board, one relay board, power supply for ESP8266 and I kinda feel of wasting the space with the third board.

Is there any other options besides current sensor?