This is a standard PCB-mountable barrel-type jack for DC power adapters with 2.1 mm center holes.
|Dimensions (in mm) for the DC power adapter barrel jack.|
The jack has three pins: pin 1 comes out of the back of the jack and is connected to the center 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 adapter plugged into the jack, pin 3 is disconnected. This feature makes it easy to create a system that is powered by a wall adapter when one is plugged into the jack and by a battery the remainder