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What Is a Rotary Switch?

Classic black rotary dial telephone, which contains a rotary switch.
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  • Written By: M. McGee
  • Edited By: Lauren Fritsky
  • Last Modified Date: 19 August 2014
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A rotary switch is a switch that is operated by turning rather than flipping or pushing. The switches were common in devices that needed to provide a wide array of options rather than the two or three provided by the other switch types. A rotary switch consists of a single pin, called a rotor, that has one or more flat wheels connected to it, called decks. When a user turns a knob, the rotor turns the decks and changes the way they connect to the device. This creates a wide array of different possible settings.

Analog switches were common on devices until the mid-1970s, after which digital switch became more common. These switches had three basic styles: buttons, toggle switches and dials. A button was off or on based on whether it was pushed in or not. A switch could be an on/off system like a button or it could have an intermediate third position, but it would commonly switch a device between operational states. Basically, one position caused a device to act one way, but the device would act differently when switched.

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Dials, or a rotary switch, would allow users to have a variety of different settings all on the same switch. Each deck could have multiple predetermined settings, usually having four to eight physical notches that let the switch click into place. By using multiple decks, a rotary switch could have a wide array of options simply by staggering the notches and setting up a coding system. For example, the third, fourth and first position on the three decks will yield a different result than the third, fourth and second position.

Dials were common on most electronics of the time, but were found on nearly every television and phone. The rotary switch on the phone was so integral to its function that it was known as a rotary phone. In this case, the rotary system would use the signal coming from the deck to determine the number that the user wanted. It would essentially count the clicks between when the user stopped and the dial reset. This is why not letting the dial return all the way to its original position or using a finger to slow the return would often cause the phone to misdial.

Televisions also used the common rotary dial system. Older TVs would feature two dials, one that set common channels and one used for the ultra-high frequency (UHF) channels. Typically, the UHF dial was inactive unless the main channel dial was set to a specific spot, usually marked with a capital U. Then the UHF dial, which typically featured dozens of channels, would allow the user to access the extended band. In this case, the dial worked similar to a toggle switch; by setting the main dial to U, it changed the operational state of the television.

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Soulfox
Post 2

@Melonlity -- one of the quickest ways to get around the problems associated with wiring a rotary dial so it could be changed remotely was the good old cable box. One could simply set the dial to a default channel (usually "3") and pass signals from a cable box directly into a television set. The cable box could then be controlled with a remote.

By the way, when it comes to rotary dials do light switches still use that technology for "dimmers" or are those all digital now?

Melonlity
Post 1

Keep in mind that those old rotary switches on televisions were a major obstacle to using remote controls on them. There were more than a few ways developed to allow remotes to change channels, but they were clumsy and prone to breakage. Thank goodness for all digital tuners, huh?

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