A rotary switch is a switch that is operated by twisting. It consists of a rotor and one or more decks, allowing for a wide range of settings. Analog switches were common until the mid-1970s, with push buttons, toggle switches, and dials being the three basic styles. Rotary switches were commonly found on telephones and televisions, allowing users to select different numbers or channels. The UHF dial on older TVs functioned as a toggle switch, changing the operating state of the TV.
A rotary switch is a switch that is operated by twisting rather than flipping or pushing. Switches were common in devices that were supposed to provide a wide range of options rather than the two or three provided by other switch types. A rotary switch consists of a single pin, called a rotor, to which one or more flat wheels, called a deck, are attached. When a user turns a knob, the rotor spins the decks and changes how they connect to the device. This creates a huge range of different possible settings.
Analog switches were common on devices up until the mid-1970s, after which digital switches became more common. These switches came in three basic styles: push buttons, toggle switches, and dials. A button was off or on depending on whether it was pressed or not. A switch could be an on/off system such as a push button or it could have an intermediate third position, but will normally toggle a device between operating states. Basically, one position made a device act one way, but the device behaved differently when switched.
Dials, or a rotary switch, would allow users to have a variety of different settings on the same switch. Each deck might have multiple predetermined settings, usually with four to eight physical notches that allow the switch to click into place. Using multiple decks, a rotary switch could have a wealth of options by simply staggering the notches and setting up a coding system. For example, third, fourth and first position on the three decks will produce a different result than third, fourth and second position.
Watch faces were common on most electronic devices of the time, but were found on nearly all televisions and telephones. The rotary switch on the telephone was so integral to its function that it was known as a rotary telephone. In this case, the rotary system would use the signal from the deck to determine the number desired by the user. Essentially the clicks between the user interrupting and resetting the watch face would count. This is why not letting the dial fully return to its original position or using a finger to slow it back often causes the phone to misbehave.
Televisions also used the common rotary dial system. Older TVs would have two dials, one that sets common channels and one used for very high frequency (UHF) channels. Typically, the UHF dial was inactive unless the main channel dial was set to a specific point, usually marked with a capital U. So the UHF dial, which typically featured dozens of channels, gave the user access to the extended band. In this case, the dial functioned similar to a toggle switch; by setting the main dial to U, it changed the operating state of the TV.
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