Sensing whether a device is on

Configuration
1

I’m looking at how I can monitor whether one of my alarm outputs are activated, which I assume are low voltage.

I considered going straight from the alarm output to sonoff SV, but then when the output isn’t activate then the sonoff will just show as unavailable since it will be off.

I could use the alarm output to trigger a 220v relay, which I can then use to measure the current with a POW - but again, if the output isn’t triggered then the POW will be off.

I’d need something that stays on, but that can detect accurately on whether the output is activated or not?

Any pointers to a similar project that could help?

2

Find out exactly what this is first. Then it is easier to offer options.

3

Had a look at the alarm documentation and the outputs appear to be 12v

4

Ok, what other types of devices do you have?

Zigbee, ZWave, Wifi?

Would prefer a commercial device or DIY?

Obviously there is going to be some diy involved, no matter what, as you have to connect to the existing wiring.

5

All my devices are currently Sonoff, which are flashed with Tasmota. So all using Wifi.
I would consider both commercial and DIY options, whichever is going to be a more viable option.

6

Got further feedback from my alarm company which changes things a bit:

The outputs on the Premier 816 control panel are switched 0V outputs. This means they apply 0V when active. When inactive they are pulled up to 12V.

7

Aright let’s stick with what you know. The Sonoff SV seems like a good candidate.

You will need a constant 12V source from somewhere in your alarm panel to power the SV. This shouldn’t be too hard to find.

Connect the alarm wiring via resistors as shown:

Alarm Signal(+) ------[8.2K Ohm]----T-----[2.4K Ohm]------ Alarm signal GND
                                    |
                                    |
                                 To GPIO x

Two resistors in series (the order shown is important) to convert the 12V to 3.3V at the tap point which you can connect to any of the GPIO pins on the SV to sense the alarm voltage.

Set that GPIO in Tasmota to be a switch input. Set SwitchMode 2 to invert this switch (0V = ON).

8

Thanks @tom_l, this looks simple and like a good solution.
To test before connecting to my alarm I could use a second another 12v source and when it’s powered on the Sonoff should show off and visa versa.

Excited to give this a go, will update this thread once complete.

9

Just wanted to confirm, once everything is connected I’ll only have 3 wires connected to my Sonoff SV:
Wire 1 and 2: The SV’s 12v power source +'ve and GND
Wire 3: One wire connected to my GPIO which is tee’d off from the alarm signal wire

10

Correct.

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