What is a Rotary Switch : Working & Its Applications

A switch is a device designed to disconnect electricity from a circuit. It can close or open a circuit. All electrical and electronic applications use one or more switches to turn a device on and off. Therefore, the switch is part of the control system and cannot be controlled without it. The switch has two functions: fully ON (closing the contact) or fully OFF (opening the contact). The switches are divided into electronic and mechanical switches. This article describes the working principle, circuit diagram, types, and interfacing of one of the types of mechanical switches called a rotary switch.

Rotary Switch Definition:

Rotary switches are multifunctional electromechanical switches that can be a great alternative to pushbutton switches. Designed to rotate and turn 360° or move to the next position with an internal rotating pin that allows the cap to rotate. The main characteristic of rotary switches is that they can be used to control different circuits or controls with a single switch. These switches are available in various sizes, shapes, and materials.

Theory of Rotary Switches

Rotary switches are used to connect the functional circuit of the device to the power supply. The electrical charge enters the switch and then transfers to the circuit currently selected by the switch. Unlike software systems such as touch screens, rotary switches are a powerful machine control system that provides immediate tactile feedback. In some cases, software bugs can be dangerous or cause serious problems. The single Pole 3-position rotary switch is shown below.

Some of the more popular applications of rotary switches are variable speed fans, rotary light switches, dimmers, professional audio splitters and converters, 3-way rotary and 6 position rotary switch guitars to switch between different effects and tones, handheld radios to switch between different bands and channels, voltmeters and similar gauges, car dashboards for adjusting functions of air conditioning or fans, Aircraft control panels, Various industrial, medical, construction and military communication devices, e.g. speed control of conveyor belts, frequency control of oscilloscopes, control of diagnostic equipment.

Circuit Diagram of Rotary Switch

Used to connect a line to one of several lines. Examples of such switches are range selectors in electrical measuring equipment, channel selectors in communication equipment, and band selectors in multi-band radios. It consists of one or more moving contacts (called buttons or knobs) and one or more fixed contacts. This switch can be used on different contact point configurations such as 12-way single-pole, 3-pole 4-way poles, 2-pole 6-way, and 4-pole 3-way.

Consider an application of brightening the lamp using the Double Pole Single Throw Rotary Switch (DPST rotary switch). The circuit diagram of the DPST rotary switch for glowing the lamp is shown in the figure below. Note that the Pole represents the switching function of the number of circuits. While the no. of throws represent the no. of states to which the current can flow through the switch.

The DPST rotary switch consists of 4 terminals: 2 input contacts and 2 output contacts. It works like two separate SPST rotary switch configurations operated at the same time. Although there is only one ON position, each input contact can be connected to the corresponding output contact by activating both contacts at the same time. In the OFF position, both switches are open. This type of switch is used to control two different circuits at the same time. In addition, the contacts on this switch can be configured as normally open or normally closed.

When the switch contacts are closed, the switch creates a closed path through which current flows, so the load absorbs the energy from the source. Then the lamp glows. When the switch contacts are open, no power is absorbed by the load.

Another important function of this switch is to divert the current flow in the circuit. Consider the second circuit as shown above to operate the motor and glow the lamp at the same time using the rotary switch.

Rotary Switch Working Principle

Let’s see the basic rotary switch working principle. Even though various designs and configurations are available, they all have the same basic design, such as a spindle or a rotor. As the spindle rotates on its axis or shaft, the spoke moves to different positions, making contact with the corresponding electrical terminals and activates a connected circuit or changes an electrical state (for example, from on to off state). This circuit passes through a circular component called a wafer. Several circuits can be connected in one place.

Most rotary switches have a star or notch-designed wheel rather than a smooth surface. This avoids stopping in an. intermediate position between contact points or terminals. For the same purpose, a spring mechanism called a detent can be installed.

The terminals are usually placed around the spindle at fixed rotation intervals (usually 30°, 45°, 60°, and 90°). This angle determines the number of available switch positions. The number of user-selectable positions can be limited by some rotary switches by inserting washers into specially designed slots. For example, if you need a 12 position switch, switch to a 4 position switch.

Rotary Switch Types

The most widely used rotary switch types are explained below.

Wafer Rotary Switches

In this type of switch, the wafers are the components, which can distribute the power/electricity to the output terminals from the spindle. These are available in a special design, in which contacts are fixed on both sides of the wafer.

Yaxley Rotary Switches

These are traditional rotary switch designs and are used very rarely.

Miniature Rotary Switches

These types of switches are specifically designed to use in settings, where space is considered a premium. Example printed circuit boards or circuit boards. They are fully closed or fully open and frequently used as sensors for the detection of other components’ positions.

High Current Rotary Switches

These are designed for high voltage circuit applications. These are made up of ceramic material, which can provide resistance to electrical discharge. The contact points and casing are reinforced.

Rotary Cam Switches

These types of switches come with a shaft that can increase or decrease the electrical resistance at the connected contact points. They are a good choice for AC-powered electronic instruments.

Rotary DIP Switch

A rotary DIP switch is a group of switches located in a dual in-line package, a standard configuration commonly used on PCBs and other electronic components. These switches, also known as dual in-line switches (DIL switches), are used to control the electrical response of installed devices.

Momentary Rotary Switch

Momentary rotary switches are used in various electrical circuits to provide an immediate change of state, such as the Switching function from one circuit to another or from on to off state. Press the switch to return to the default position.

Binary Rotary Switch

It is another compact designed rotary switch for use in sensitive electronic equipment. It uses a binary on/off the system.

Heavy-duty Rotary Switches

These can provide robust mechanical control in harsh industrial environments. The accessories and optional components of the heavy-duty rotary switches include caps, knobs, replacement dials, shaft assemblies, spindles, rotating open circuits, and lock systems.

PCB Mount Rotary Switches

These are upright controls mounted on PCBs and are used for controlling multiple output terminals.

Rotary Encoder Switches

These are PCB switches specifically designed for controlling and monitoring the various functions with larger circuits.  These are considered rotary switches due to their rotational functionality inside.

Based on the different combinations of poles, throws, and ways, the switch is divided into various configurations. Generally, the rotary switches are referred to as single pole and double pole rotary switches that relates to the control of circuits by the switch.

SPST Rotary Switches (Single Pole Single Throw Rotary Switches)

These are used to break or make the connection of a single conductor in a single-pole circuit. These are also called single-pole switches with two terminals.

SPDT Rotary Switches (Single Pole Double Throw Rotary Switches)

These are used to close (make) or open (break) the connections of a single conductor from other two single conductors. They have 3 terminals and are usually used in pairs. They are sometimes referred to as 3-way rotary switches.

DPST Rotary Switches (Double Pole Single Throw rotary switches)

These are 4-terminal rotary switches used to connect or disconnect two circuit conductors in one branch circuit or two branch circuits.

DPDT Rotary switches (Double Pole Double Throw rotary switches)

These are used to connect or disconnect two wires to two separate circuits. They have 6 terminals available in both maintained and momentary contact versions.

DP4T Rotary Switches (Double Pole Four Throw Rotary Switches)

These are most commonly used in televisions, radios, industrial settings, and home lighting systems.

8-Pole Rotary Switches

This popular design allows easy selection of input poles or terminals.

2 Positions 2 pole Rotary Switches

In this design, a double pole is connected to two selectable positions.

2-pole, 6-position Rotary Switches

In this design, each pole is connected to three selectable positions.

Multi-pole Rotary Switches

The standard version of the rotary switch is a single pole. The multi-pole model provides more flexibility.

DP3T Rotary Switches (Double Pole Three Throw Rotary Switches)

In this design, two separate circuits intersect at 3 different points and provide 3 selectable switch positions.

Rotary Switch Arduino/Rotary Encoder Switch Arduino:

The rotary switch or rotary encoder switch is an electromechanical switch that can convert the angular movement of the shaft to either digital or analog code. It comes under the position sensor type that converts the angular position (rotation) of a knob into an output signal to determine the direction of the rotation of the knob. These types of switches are mainly used in radio equipment like amateur radio or handheld,  where continuous 360 degrees rotation is necessary for perfect frequency tuning.

This section explains the interfacing of a rotary switch or rotary encoder switch with Arduino. The components required are,

• Rotary Encoder switch or Rotary switch.
• Arduino UNO.
• LCD.
• Connecting wires.

The circuit diagram of the rotary switch Arduino is shown in the figure below. From the circuit, the coding pins (CLK and DT pins) and switch pin (SW pin) of the rotary encoder is connected to pin 2, pin 3, and pin 4 of Arduino. Here a 20×4 LCD is used to display the objects of the menu. Pin RS and pin E of the LCD is connected to pin 5 and pin 6 of the Arduino. While the data pins 11-14 (D4-D7) of the LCD are connected to the Arduino pins 7-10.

These switches can provide infinite rotation in either clockwise or anticlockwise direction with a knob or select button. With this unique functionality, these are commonly used in applications of ‘menu’ selection. The shaft of this switch is rotated in a clockwise or anticlockwise direction to select or browse the contents of the menu. By pushing the knob or select button, the highlighted menu content can be selected. It is mainly used for normal switching operations and can be implemented as a selector switch (as menu selector) using Arduino.

The rotary switch/rotary encoder switch works as a menu selected when it is interfaced with the Arduino and LCD. The Arduino code is written and uploaded to Arduino as per the application.

If the rotary encoder’s shaft is rotated in a clockwise direction, then the menu content will change from left to right and highlight each menu item for every rotation of the knob.

On reaching the last item, further rotation doesn’t result in any action and the last menu item gets highlighted.

When the knob is rotated in an anti-clockwise direction, then the contents of the menu are highlighted in the opposite direction and displayed below the contents (items) list.

By pushing the button of the rotary encoder switch, any one of the highlighted items can be selected. This is displayed on the LCD as the selected item and it remains until the next item is selected.

Function of Rotary Switch

Unlike pushbutton switches, which can be used in either momentary or latching device control functions or functions. The rotary switch can be used for maintaining or latching functions to on/off. That means when moved to one position, the rotary switch remains in place and must be moved again to perform the next function.

• It is a multifunctional and multi-purpose switch that can control various functions.
• These are classified as HMI (Human Machine Interface) components because they allow the operator to interact with and control the device.

Rotary Switch Vs Selector Switch

The differences between rotary switch and selector switch are;

Rotary Switch	Selector Switch
A rotary switch is a switch in which contacts and connections alternate when the spindle is rotated clockwise or counterclockwise.	The selector switch turns/rotates the handle to turn the circuit on or off at different currents.
Controls different circuits with a single switch.	Commonly used for control, it consists of a mechanical, electrical, or electronic device for making/closing, breaking/opening, or changing connections in a circuit.
These are available in different sizes, materials, and shapes with different contact point arrangements such as 3-pole 4-way, single Pole 12-way, 2-pole 6-way, and 4-pole 3-way.	They are available in 2 and 3 positions, and they can be illuminated and non-illuminated selector switches.
Used in medical equipment, industrial controls, computers, instrumentation, communication, and aircraft equipment.	Used in automotive, industrial controls, building, and public Works, control system panels, medical equipment, commercial and domestic appliances, and home automation devices.

Advantages and Disadvantages

The rotary switch advantages are:

• This switch can make circular movements and can stop or interrupt in various positions.
• These are designed to operate multiple contacts simultaneously using the same switch position.
• This device has several advantages over other switches because the rotation of the actuator can turn the circuit on or off depending on the position, and allows for different actuation positions.

The rotary switch disadvantages are :.

• These switches are rarely used as complex switching tasks are performed using digital devices such as touch screens.
• However, mechanical rotary switches are still used, especially in devices where damage to the computer could be a security risk.
• Cost is more.
• More issues in broadcasting.
• Wear out of mechanical component with time.
• Physical contact is necessary.

This is all about an overview of a mechanical rotary switch – working with applications. There are a wide variety of rotary switches available in the market. Choose the right one for the project. Here is a question for you, what is a flow switch?