Ive made this design withc worked at first, but now I dont know why the micro controller does not drive the reley anymore. when I measure the D0 output it shows 3.6V, when it should be 5v. Ive tried using an arduino pro mini instead, but its the same, no improvement.
I just figured it out :D:D:D. It was the relay. I connected another relay and it works. I don`t know what happened with the other one, because when I connect it to 5V directly, it makes the click sound.
Is the relay coil connected directly to the Arduino, or is it a relay board with a driver circuit?
If the relay is connected directly to the Arduino, what's the current rating on the relay coil? (I assume it's rated for 5V?)
The Arduino is rated at 40mA maximum and if the relay coil requires more than that, it won't work reliably. ...Even at 40mA it could be marginal because the 5V will drop somewhat with the maximum load.