Author Options:

Multiple Arduino Uno I/O ports driving relay Answered

Understand that the Arduino Uno can output a maximum of 40mA each from its IO port. I used 2 IO ports each (4 in total for switching) to drive a 80mA relay. In this case, the Arduino Uno is powered by USB, which draws up to 500mA. It worked and it was left to switch for a few minutes on pulsed 10 seconds interval. However, the Uno board heats up to around 50-55 degrees centigrade. Will this damage the board?



Best Answer 3 years ago

Probably. The 2 outputs don't really work as a single output neatly providing half the current required each. + the relay will almost certainly draw more current then specified - they just do.

+ the inrush current as the relay operates will be more then 80 mA

I suggest you drive a small transistor with a single output via a 1K resistor and put the relay in the collector cct.


3 years ago

The only way to make it work, and its not something better than using a transistor is a small resistor on EACH output, coupled to the relay, something like 10 Ohms usually works, this will allow the outputs to share the current properly.