Detect if light is turned on

    Summmary: I want to read over internet whether a circuit is open or closed. Is this possible with the Shelly 1?

    The control unit of my sauna has 24 DC output to connect a lightbulb. The lightbulb turns on when the sauna heater is on, and turns off when the sauna heater is off. I want to be able to read from the internet (e.g., the shelly API) if this circuit is on/off.

    See pins 1 and 2 of the sauna control unit diagram.

    My idea was to use a shelly 1 device instead of an indicator lamp. The connections I had in mind were:

    Shelly I: sauna terminal 2

    Shelly O: sauna terminal 1

    Shelly SW: empty

    Shelly L: wall plug (e.g., 220 V AC)

    Shelly N: wall plug (e.g., 220 V AC)

    The shelly device relay would be set to always on. Could I then check with API if the circuit is open or closed? For example with the endpoint: https://shelly-api-docs.shelly.cloud/#shelly1-1pm-relay-0

    Thanks for your help!

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    I and O are open/closed based on how you've configured the behavior of SW, so in your example it will always show on because the switch is always on. The shelly1can't tell you whether the circuit connected to I/O is closed or power is flowing -- you'd need a 1P, EM, etc. for that.

    If you want to detect circuit closure with the shelly1 then it has to go through the SW contact with the switch configured for "disconnected" mode so the state of SW no longer controls I/O. However, the L/+ (hot) wire also feeds the SW input on the shelly1 (which is connected to -/N to close the switch), so whatever is connected from SW to ground has to be able to handle the voltage supplied by +/L.

    In your application, your switch is introducing 24VDC, so not a good choice. There is a way to make your application work with the shelly1 but requires an additional component: an electrically isolated relay such as this one I've used in several projects:

    https://www.functionaldevices.com/products/build…details/RIBU1C/

    Essentially you would take your 24V switched circuit and wire it into the DC (10-30V) and Common on the relay's inputs and the N/O (normally open) and (C)ommon side (dry contact in this case) to +/L and SW on your shelly switch. This way, when your 24V switch is closed the relay will close the dry contact side, and the shelly1 will display input/0 as "1". When the 24V switch is opened, the relay opens the dry contact side and shelly1 will display input/0 as "0". You can power the shelly with AC or DC as long as it's within the tolerances of the RIBU1C (or relay of your choice), which is the nice thing about using a relay like this as you can mix AC/DC/voltages because the RIBU1C isolates each side.

    I've used RIBU1Cs and shelly1s in disconnected mode to control and monitor my garage doors.

    I/O is used to toggle the door into opening/closing (I have the shelly automatically turn it off after 1 second to simulate a momentary button press when triggered) while the SW/- inputs are connected to a reed switch that's normally closed (NC) when the garage door is closed. I also power my shellies in this application with 12V DC which the reed switches can handle (again, because the L/+ voltage on the shelly is routed "out" through the SW to ground).

    Good luck.

    -Jason