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Rotary switch

technology Maturity 11-13 Next article →

A rotary switch is a mechanical device used to control electricity.

rotaryswitch
rotaryswitch

It is designed to manage multiple electrical paths through rotation. This makes it very useful for complex machines. You might use one to choose speeds on a fan. It could also select different frequencies on a radio. These switches are ideal when a device needs more than two positions. They allow a user to connect different circuits with a single turn.

The mechanism of a rotary switch relies on moving parts. At the center is a spindle known as a rotor. A small contact arm called a spoke projects from the rotor. This spoke acts like a cam to make connections. Around the rotor sits an array of terminals arranged in a circle. As the rotor turns, the spoke moves from one terminal to the next. Each terminal serves as a contact point for a specific circuit.

rotaryswitch
rotaryswitch

To prevent errors, many switches include a detent mechanism. This mechanism provides a physical "click" during rotation. The click helps the switch move into an active position. It prevents the rotor from stalling in an intermediate position. Stalling in the middle could mean the circuit is not fully connected. This ensures that the user always selects a complete and stable path.

rotaryswitch
rotaryswitch

Rotary switches can be built with different layers to increase capability. Each individual layer is referred to as a pole. By layering these poles, a single switch can control multiple circuits at once.

rotaryswitch
rotaryswitch

Some designs limit the rotation to a fraction of a full circle. A switch might only rotate a third or a half of a circle. Even with this limited movement, each layer can still hold multiple poles. This design provides greater pole and throw capabilities than simpler switches.

Modern rotary switches often use a star wheel mechanism for precision. This mechanism allows for specific switching positions. These positions can occur every 30, 45, 60, or 90 degrees.

rotaryswitch
rotaryswitch

Behind this wheel, nylon cams are mounted to guide the movement. Spring-loaded electrical contacts slide along these cams. The cams feature notches or cuts in specific places. When a contact reaches a notch, it closes the electrical circuit. This process ensures very accurate switching in modern electronics.

These components have a long history in various technologies. Before the early 1970s, rotary switches were common in television receivers. They served as the channel selectors for those sets. They were also used as range selectors in electrical metering equipment. Multi-band radios used them as band selectors to change frequencies. These tools were essential for managing the many functions of older electronic devices.

Some rotary switches are also user-configurable. This means a person can change how many positions the switch has. This is done using a special toothed washer. The washer sits below the holding nut of the switch. You can position a tooth into one of several slots. This limits the number of available positions for the user. For instance, you could take a twelve-position switch and limit it to four.

rotaryswitch
rotaryswitch

This flexibility allows the switch to be tailored to specific needs.

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