You can set up a simple electronic circuit to connect and disconnect your battery pack from any circuits you build on a solderless breadboard without having to physically remove the battery pack from the breadboard.
In the following figure, the positive terminal of the battery is connected to the top terminal of an SPDT switch. The center terminal of the switch is connected to the leftmost column of the breadboard, which is also known as a power rail. By moving the slider on the switch, you make or break a connection between the positive terminal of the battery and the positive power rail. As long as you use the power rails to supply power to your circuits, your switch functions as an on/off switch for powering your breadboard circuits.
By adding a
and an LED between the center terminal of the switch and the negative power rail, you create an indicator light for your on/off switch. If the switch is in the off position, the battery is not connected to the LED, so the LED is off. If the switch is in the on position, the battery is connected to the LED, so the LED is on.
Note that even without this resistor and LED, the switch still functions as an on/off power switch for your breadboard. But it's nice to have a visible indicator that the power is on, as shown.
