This is a standard PCB-mountable barrel jack for DC power adapters with 2.1 mm centre holes.
|Dimensions (in mm) for the DC power adaptor barrel jack.|
The jack has three pins: pin 1 comes out of the back of the jack and is connected to the centre pole, pin 2 comes out of the bottom of the jack and is connected to the side wall, and pin 3 comes out the side of the jack and is automatically switched based on whether there is anything plugged into the jack. With nothing plugged into the jack, pins 2 and 3 are shorted together; with an adaptor plugged into the jack, pin 3 is disconnected. This feature makes it easy to create a system that is powered by a wall adaptor when one is plugged into the jack and by a battery the remainder of the time.