I bough a Float Switch that works with a floating on top of a liquid which opens or closes the electrical circuit as the liquid level rises or falls.
My idea was to use the ports S1 and S2 from the Sonoff Mini R4 to close the circuit and so I would be warned by Alexa the water level has gone down, however I’m affraid the S1 and S2 may not completly isolated and somehow I get 110V in the water tank.
Any suggestion? Any sonoff which I can use as a dry contact sensor?
Thanks
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I use this one and it works fine.
I think Mini R2 has some sort of low voltage sensing on S1-S2 terminals, it is written in the manual to keep inputs disconnected from Line or Neutral for safety. Also the eWeLink-Remote transmitter Sonoff S-Mate (with 3 different inputs) developed for Mini R3 should work but I didn’t test one yet. Hope it helps!
I have two floatswitches that I use in this way with the Mini R2. It works very well
If I understand correctly you are worrying about the device if so use the MINI R4
If you want a dry contact device look here https://www.amazon.com/Sonoff-Wireless-Automation-Modules-Compatible/dp/B07F6YZXST
How are they wired please since the float switch works by neutral?
A float switch operates by closing or opening a contact, depending on which of the three wires you use. One would be common, one would be normally open, the third would be normally closed. This makes it ideal for connecting to the S1 and S2 terminals of the MiniR2 - you can think of it like a light switch which is off or on, and you set the MiniR2 properties to follow the state of S1/S2. For example - when the liquid in the tank drops, the float switch closes a contact, which then triggers the MiniR2 to switch on power to a pump.
As the level of the liquid rises, the float switch contact will open and this then triggers the MiniR2 to switch off power to the pump.
Please note - you do not want to connect power to the S1/S2 terminals on the MiniR2 - it tends to blow up 
The float switch is simply a dry contact… Please refer to the MiniR2 wiring diagrams provided with the device and follow the instructions for using a dry contact connected to S1/S2.
Hope this answers your question properly.