A rotary switch is a way to control many different circuits or select many different values for one circuit with a single switch. The switch rotates in a circle, turning different circuits depending on its position. Before digital technology took off, rotary switches were commonly used on televisions to select different channels. They are still used in many applications including CB radios, industrial controls, electronic instruments and even some aircraft.
Rotary Switch Basics
In a rotary switch, the current runs into a rotating spindle, which has several different rotors on it. At each rotor, there is an arm projecting outward that can make contact with a terminal when the switch is in a certain position. A switch can have dozens of possible positions, and each one can be attached to a particular circuit.
Controlling the Switch
For the rotary switch to turn on a particular circuit, it has to be in just the right position. A rotor that rotated too freely would be hard to control and could easily get turned off or thrown to the wrong setting accidentally. To stop this from happening, rotary switches use what is known as a detent mechanism to make the switch "click" into position and stay in the same place until it is turned with enough force. A detent uses a wheel with notches or grooves cut into it attached to the rotor. There is a spring-loaded ball bearing or a piece of spring steel pressing against the wheel. When the wheel reaches the correct position, the bearing or piece of steel presses into the groove, holding it into place until someone twists the rotor and moves it to the next groove.