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Commonly used Switches in Electronics

In this post today, we will look at many types of switches. This article will guide you on how to choose the right switches for your applications.

What is a Switch??

A switch is a device that is designed to interrupt the current flow in a circuit, in other words, it can make or break an electrical circuit. Every electrical and electronics application uses at least one switch to perform the ON and OFF operation of the device.

When current can flow from one contact to another, the switch is ON and is said to be closed. When there is a separation preventing the current flow between the contacts, the switch is OFF and is said to be open.

Where are these Switches used??

There are numerous applications found in a wide variety of fields such as home automation, automobiles, industrial, military, aerospace, etc.

 In some applications, multi-way switching is employed (like building wiring), in such cases two or more switches are interconnected to control an electrical load from more than one location.

So What are the Different Types of Switches??

The Switches are differentiated based on their robustness, environmental resistance, and other characteristics. Switches come in a variety of shapes and sizes. Switches are normally classified into how the contacts are arranged. 

It can be a simple on-off type switch or it can have multiple positions that can control a different speed of a fan or like that. Basically, switches are of two types. One is a mechanical switch and the other is an electrical switch.

Mechanical Switches:

Mechanical switches must be activated physically, by moving, pressing, releasing, or touching their contacts.

Electronic Switches:

Electronic switches do not require any physical contact in order to control a circuit. These are activated by semiconductor action.

Normally a switch has two terminals – Poles and Throws.

Poles and Throws:

Pole refers to the total number of circuits that are controlled by the switch: Single Pole switches control only one electrical circuit. Double Pole switches control two or more independent circuits.

Throw refers to the number of output paths in which a current can flow. For example, a double-throw switch consists of contact capable of being connected to one of two other contacts.

Normally open and Normally closed:

In a normally open switch, when the switch is off, the contacts are open. This means the electrical connection is broken so the switch is “off”.

Image Courtesy: InstrumentationTools

 In Normally Closed switches, the contacts are closed which connects the switch meaning that when they are not compressed they are switched “on”.

Image Courtesy: InstrumentationTools

A switch with both types of contact is called a changeover switch or double-throw switch.  A changeover switch closes one circuit and opens a second circuit simultaneously. The upcoming sections contain information on the classification of switches. Such as Poles and Throws and Latch and Momentary Control.

Switches are classified based on Poles and Throws

 Single Pole Single Throw (SPST) – The switch contains one circuit with NO or NC contacts.

SPST switch is a basic on-off switch. It can control only one switch. This type of switch has two terminals:  the input terminal is a pole and the output terminal is a throw.

The following is the circuit diagram of the single pole single throw switch. When the contact of the switch is closed, the current will flow and makes the lamp bulb glow.

In the above circuit, when the switch is not pressed the contacts are separated. When the switch is pressed, the contacts will close. An example of an SPST switch is a light switch.

Single Pole Double Throw (SPDT) – Only one of the loads can be energized at a time. The switch contains one circuit with changeover contacts.

A Single Pole Double Throw (SPDT) switch is a switch that only has a single input and can connect to and switch between the 2 outputs. This means it has one input terminal and two output terminals. A Single Pole Double Throw switch can serve a variety of functions in a circuit.

It can serve as an on-off switch, depending on how the circuit is wired. Or it can serve to connect circuits to any 2 various paths that a circuit may need to function in. For example, an SPDT switch can connect to create a Ready Mode and a Standby Mode in a printer.

Double Pole Single Throw (DPST)– Both load terminals can be energized at the same time. The switch contains two circuits with NO or NC contacts

This switch has two input terminals (pole) and two output terminals (throw). We can say this type of switch has two SPST switches in one package. Both switches can be actuated at the same time because they are connected side by side to a single liver. So when a contact is closed, the current flow makes it actuated.

Double Pole Double Throw (DPDT) Functions like two separate SPDT switches operated by the same actuator. only two loads can be ON at a time. The switch contains two circuits with changeover contacts.

This type of switch has two input terminals (pole) and four output terminals (throw) two for each pole. This is similar to two SPDT switches and works at the same time. It works like an SPDT switch.

It is easy to understand the working of the DPDT switch if we see the circuit below. Here we used the DPDT switch to reverse the polarity on a motor. The positive(+ve) side of the motor is connected to 1st switch throw-1 and to 2nd switch throw-4. 

The negative(-ve) side of the motor is connected to the throw-2 of the 1st switch and throw-3 of the 2nd switch. In the 1st position, the motor will rotate in a clockwise direction. When we change the position of the switch, the power supply is reversed and the motor will rotate in an anti-clockwise direction.

Based on Latch and Momentary Control

Momentary control switches are normally open or normally closed. The switch is ON only while it is being pressed.  It turns OFF when it is released, for example, a push-button.

 A latching switch needs to be pressed once for ON and again for OFF, for example, a light switch.

Push Button Switch

A push-button may be normally open or normally closed. When the button is pressed, the contact will be closed and the current will flow in the circuit. The circuit remains closed as long as the button is pressed. Whenever the pressure is released from the switch, it is now normally open.

Reed Switch

Reed switch has two metal contacts called reed which is made from a ferromagnetic material and is sealed inside a thin glass. In a reed switch, the contacts will close when a magnetic field is applied near them. When a magnetic field is removed, the contacts will be opened.

Toggle Switch

A toggle switch is a basic ON-OFF switch. It can be actuated by a mechanical lever placed at the top which controls the current flow in the circuit. The lever can be pushed up and down or left and right to open or close the contacts. They are available in SPST, SPDT, DPST, DPDT contacts terminology with two or more lever mechanisms.

Rocker Switch

The Rocker switch is also an ON-OFF switch that rocks when the switch is pressed. It has a seesaw connection to open or close the contacts. These switches can be widely seen in houses. It is also called a seesaw switch because when one end of the switch is raised, the other end is lowered. It is used for switching the circuit.

DIP Switch

DIP is a dual inline package switch. It can be mounted onto the PCBs to make settings on electronic devices such as hard drives, modems, and motherboards. It has a sliding pin as switch contacts. These are arrays of SPST switches. These can be either set as ON or OFF.

The DIP switch can create an electrical signal that provides a binary signal to computers that use the numbers 0 and 1 to perform complex calculations. The values of all switches in the DIP package can also be interpreted as one number.

For example,7 switches of one DIP Switch offer 128 combinations, allowing them to select a standard ASCII character whereas 8 switches of one DIP Switch offer 256 combinations.

There are many types of DIP switches. They are slide DIP switch, rocker DIP switch, and rotary DIP switch.

Slide Switch

The slide switch has a slide-like knob called an actuator that can be moved back and forth to open and close the contacts. The metal pins at the bottom are called terminals. The terminal in the middle of the switch makes a connection with one of the terminals at each end, depending on which way you move the actuator.

Rotary Switch

A rotary switch is a switch in which the contacts are changed when the spindle is rotated in either a clockwise or an anticlockwise direction.  It can stop in different positions. They are used for connecting one line to one of many lines. This switch is like a single pole and multi-throw switch.

Limit Switch

A limit switch can sense motion and detect the presence of objects when the object reaches a specific location. They activate when an object makes physical contact with the actuator. A variety of actuator types ensures that any manner of machine, component, or object can be sensed by a limit switch. Limit switches have normally open and normally closed contacts. they are robust and can provide high precision.

Hall Effect Switch

Other than the above, Hall-effect switches are momentary push-button switches that use hall effect sensor technology for contactless switching. These switches are designed to withstand harsh environments and are used in devices that carry high loads, heavy equipment and industrial machines.

Key Lock Switch

This switch is an OFF-ON momentary switch that is used in cars or vehicles. The switch is in the ON position until the vehicle is started. The momentary position will start the vehicle and return back the switch to the ON position. To turn off the vehicle, the switch is to be turned OFF.

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