Rotary switches provide a convenient method for selecting an exclusive circuit connection among several merely by turning a rotary knob to a discrete position. They are also called selector switches. While electronic test equipment, scientific apparatus and various communications equipment have always used rotary switches, many people learned to use them while twirling the channel knobs of early television sets among the 13 channels that were available in TV's formative period during the 1940s and 1950s.
Early circuits allowing various connection options as a normal course of operation used plugs and jumpers, similarly to old time telephone operators. Later, developers of electrical and electronic equipment provided many connection options by incorporating rotary switches which greatly sped up repetitive actions while assuring certainty of getting them right, since the positions are most often clearly labeled.
Most have a radial contactor arm that has one contact point pivoting on the center axis that can be connected to any one of many fixed contacts around the circumference of the switch. Others have a traveling contactor on the outer edge of the rotor that can bridge any two adjacent contacts around the circumference of the switch. Therefore, they are switched from one position to another and not to a point between positions. Further, contact is completely broken with the previous position prior to establishing contact in the next position as the dial or knob is being turned. Many rotary switches also incorporate a number of stages or levels of rotary switching action on a common knob shaft to further accommodate a number of poles that need to be switched simultaneously.
Most rotary switches have a knob shaft to connect to the one or more switching stages of the switch: internal contactors around the inner circumference of the switch; wire tabs or terminals on the outside of the switch that are tied to the inner contacts; a mounting provision which may be a bracket for circuit boards, or a threaded neck for panel boards, a knob and, importantly, clear labeling around the pointer on the knob.
Rotary switches can be operated manually, or driven by electric motors, or both, as is the case with the cycle selector switches on many clothes washers. Some motor applications use timer motors, as is the case with the washer. Others use stepper motors to make the switch in one smooth yet discrete motion to the next position. This configuration is used in sequencing operations.
Rotary Switches find widespread use in automotive applications where they may be used for headlights, windshield washers or heater fan speeds. Tools such as volt-ohm meters have long used rotary switches to allow selection of operating modes. Appliances like blenders may have rotary selectors with ten or more positions allowing every action from coarse chop to fine puree.
