Turn Off/Stop Running Arduino Board

Hi all, I am newbie to arduino development. May I know how to turn off/stop running arduino board? The reason I want to turn off arduino board is to unplug/plug wire/LED/ultrasonic sensor on the breadboard/arduino board during tinkering. I am afraid of causing damage to arduino board, sensor, LED if I just unplug/plug them onto breadboard when arduino board is still connecting to computer via USB cable.

You can’t turn off a microprocessor without :-

  1. holding it in reset or
  2. removing the power.

Holding it in reset means all the input / output pins go into a high impedance tri-state mode but there is no switch on the Arduino to do this you would have to wire one up yourself.

The best bet is to unplug it as USB is hot swappable, that is it is designed to be plugged and unplugged when powered up.