Correct resistor to prevent damage if shorting wires on Arduino output

Projects General Guidance
1

Hey Guys,

I have a project I'm building that I'll be giving to friends who'll be hooking up an LED. The LED is rated at 1.7 volts (2.4 volts max) and 20 mA. Since the output of the Arduino is 5 volts I figured I need a 180 ohm resistor right. That would put 3.3 volts across the resistor and flow approximately 18 mA.

My concern is when my careless friends short out the wires going to the LED. That would be like connecting the output pin of the Arduino to ground with only 180 ohm resistor. At 5 volts now across the resistor I work out that would still only flow 27 mA and the Arduino would be fine since max rating is 40 mA per output pin.

Am I working that out right? Need someone to double check my calculations before I burn up some Arduinos :slight_smile:

Thanks
Malcolm

2

Your calculations are all correct.

3

CrossRoads:
Your calculations are all correct.

I appreciate the double check. Cheers.