I am looking to connect the alarm outputs from the CCTV recorder to an Arduino so send an MQTT topic when an alarm is triggered.
The alarm outs at either high or low (+5v or 0V) with a common gnd on the cctv and individual alarm outs for the high or low out.
Stupid question, how can I connect these up as the Arduino will have a separate gnd and power?
the only thing they will share is they will be on the same 240v supply - Arduino via a psu.
I think you would need at least GND to be shared by the two components.
Anyway if your alarm outs a simple high or low signal, and it is +5v or 0v as you said, you can simply measure that voltage using an analogRead() call on an analog pin, having +5v as the Arduino reference voltage. I guess that will require the board to share GND with the CCTV, as I've never tried in other ways.
Thank you for that
I was assuming I would need to shard the Gnd, that's the but I was worried about.
I could power the Arduino from the USB out on the CCTV, just didn't want to take that one up!
I was going to use a digital pin as it just needed to be high or low, and I think I am right in thinking a 5v high will be fine for the board.
Using the CCTV usb cable would be fine as it already shares the gnd with the board in that way,
and of course a +5v high signal will be fine for and Arduino Uno, as the Microcontrollers can handle digital signals from 0v (low) to +5v (high) so you are good to go
was planning to use a node MCU - but these can use 5v too.
Just didn't want to use the usb, but think I will have to