I'm Working for Home Automation system through raspberry pi, I'm turn on/off lights and A/C through Raspberry pi(build application of web, to control lights/AC) either case AC switched on with physcical switch board, i need to update this value to web interface so that i know that AC is power on through swich board. How it possible to read state of the AC.

2 Answers 2


Your "physical switch board" would need some indicator of the power state of the relay or switch that's readable via a low-voltage system. Assuming that's available, you'd read that via a second GPIO pin to keep the current status independent of what signals you've sent via the control pin.


In similar projects, I check the GPIO value of that pin.

In my case, the relays are active when it's low, so a 0 value means it's on.

If you're looking to -double check- the value, then have you considered photo-diodes or similar light sensors?

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