Introduction to Relay, its Working and Types

In this tutorial, we will discuss relays. At first, we will talk about their basic introduction. Then we will discuss their uses and basic applications. After this, we will provide a brief and concise introduction to the components that relays require for proper functioning and their operation or working method. At last, we will discuss its types and applications in detail.

Introduction of Relay

A relay is an electromechanical switch that is controlled electrically. Its main use is the isolation of two circuits with different operating voltages. For example, if we want to isolate a 220-volt AC power supply from a 5-volt DC power source, we use a relay to separate them. This type of relay is an electromagnetic relay (EMR).

In many industrial applications and in control rooms where we have to control several circuits with one signal, a relay is the best device we can use. Because of its switching capability, different circuits can use it. It is basically an electrical operating switch. Most of the time, we find their use in switching the state of the circuit. Another use is for protection or isolation. Sometimes it is useful for time delays. We can also use them in PIC microcontroller projects.

Components of Electromagnetic Relay

There are three most important parts:

1. Electromagnet

In an electromagnet, there are coils of wire wound on an iron core. It becomes active when there is current or voltage in the coil.

2. Contacts

There are two contacts: NO (normally open) and NC (normally closed). When there is no current or voltage in the coil, it follows the NC path, but when voltage or current passes through the coil, it will follow the NO path.

3. Spring

It ensures normally closed and normally open contact when current passes through a coil.

Operation of Relay

Relay switching circuit (coil) based upon the DC or AC voltage. For example, when 6 volts are given across the coil, current starts flowing through it, is energized, and switches from the NC path to the NO path. Before energizing, the NC path is followed, but after switching, the NO path will be followed.


In the above figure, at points 1 and 2, the contacts are open, while points 3 and 4 show coils. When the coil becomes energized, the switch becomes closed and changes its state.

Types of Relays

Relays fall into three major categories. These are:

  1. General purpose (in which simple switching is done).
  2. Machine control (used on a large scale, such as in industries when dealing with large motors with high ratings)
  3. Reed (this type of relay) is very fast and sensitive. Free from any kind of humidity, etc.

Other types of relays are also known as solid-state relays, in which DC voltage is used as the input.

Relay Interfacing with Microcontroller

Microcontrollers do not have a considerable amount of current to operate relays. Relay coils need a minimum of 10 mA of current to energize. But the microcontroller output pin can provide maximum current up to 1-2 mA. To resolve this problem, relay driver circuits are used between the microcontroller and relay.

Solid State Relay

Solid states also have many industrial applications. These relays don’t have any coils, contacts, or springs. It is basically made up of semiconductor materials. Its switching speed is much higher than that of electromechanical relays because no mechanical movements happen inside them. Its life is also longer than EMR. They can directly interface with microcontrollers due to their very low input current requirements. Therefore, solid-state relays are an ideal choice for microcontrollers and digital circuits. They also come with phase control options. Different current and voltage-rated solid-state relays are available on the market. Like 143058CP, SSR has control volts of 4-32 volts DC and a contact current of 3 Amperes.

Applications of Relays

Relays have many uses in our daily lives, here we will mention some of them below:

  1. Power Control: In power control systems, relays have many applications. We use them for switching high-voltage and current loads. We can also use them to turn on and off electrical devices such as motors, lights, heaters, and pumps.
  2. Automation and Industrial Control: Another application of Relays is automation and industrial control systems. They have various uses in process control, machine control, and conveyor systems, providing efficient operation of various components and ensuring the proper functioning of the overall system.
  3. Home Automation: Home automation systems have many uses for relays, which include controlling lighting, security systems, HVAC (Heating, Ventilation, and Air Conditioning) units, and other household appliances. Their main advantage is the remote control and scheduling of these devices, which enhance convenience and energy efficiency.
  4. Telecommunications: We also find relays in telecommunications equipment. Their main use is to manage signal routing and switching. These relays help in the transfer of signals between different circuits. Hence, they help establish connections for telephone lines, data networks, and communication networks.


In conclusion, this tutorial provides an in-depth overview of relays. It covers basic introduction along with components and operation of a relay. Furthermore we also discuss different types of relays to help us better understand them. At the last we mentioned few major applications of the relays. You can also utilize them in your IOT projects. Hopefully this was helpful in expanding your knowledge of relays.

You may also like to read

This concludes today’s article. If you face any issues or difficulties, let us know in the comment section below.

5 thoughts on “Introduction to Relay, its Working and Types”

Leave a Comment