want to send a signal to arduino every time a 12V 1A device gets power..

I'm working on a home project. I have a device which works with 12 volt / 1000 mA. I want to send a signal to arduino uno every time this device gets power which means the device is on. How can I make arduino receive that signal ! :confused:

thank you in advance guys.. ;)

You could use an opto-isolator with a corresponding current limiting resistor. The other side of your opto is hooked up to Vcc of 5V.

Any way you do it you want to isolate your 5V circuit from the 12V circuit. Treat them separately.

Given that the 12V device and the Arduino have their grounds connected together, you take a 47k resistor from the 12V voltage that you want to sense, to an Arduino input. Just for good measure, put a silicon diode (1N914) with its anode to that input and its cathode to the Vcc line on the Arduino.

If the 12V device and the Arduino do not have their grounds connected together, then connect the 12V through a 1k resistor to the LED side of an opto-coupler and the transistor side of the opto-coupler between the Arduino input and ground, setting the pinMode to “INPUT_PULLUP”. The input will then go LOW when 12V is applied.

thank you very much for your concern guys…

yes, the 12V device and the Arduino do not have their grounds connected together…

what is the best opto-coupler to be used in this case ?

engr_aziz: what is the best opto-coupler to be used in this case ?

Used to be a 4N25, but currently an "EL817" would seem to be "the go".

|500x491 Note the link. :grin: Good Chinese supplier.

thank you very much guys.. really appreciate it :)