Encoder in Digital Electronics | Introduction, Types & Working Principle

Encoder in Digital Electronics

In digital electronics, an encoder is a device or circuit that converts a physical quantity or signal into a digital code. Encoders are commonly used to measure the position, speed, or direction of rotation of a shaft or object, and to convert this motion into digital signals that can be processed by digital electronics systems.

There are different types of encoders, including absolute encoders, which provide a unique digital output corresponding to the absolute position of the shaft, and incremental encoders, which generate a series of pulses as the shaft rotates and do not provide absolute position information.

Encoders can also be classified as rotary or linear, depending on whether they measure rotational or linear motion. Rotary encoders are used to measure the rotation of a shaft, while linear encoders measure the linear motion of an object.

Types of Encoders

Absolute Encoder: An absolute encoder generates a unique code for each position of the shaft. It provides the exact position of the shaft without requiring any initial reference point. Absolute encoders can be further classified into two types: single-turn and multi-turn. Single-turn absolute encoders can measure only one complete rotation of the shaft, while multi-turn absolute encoders can measure multiple rotations.

Incremental Encoder: An incremental encoder provides pulses for each incremental movement of the shaft. It does not provide any information about the absolute position of the shaft. An incremental encoder generates two signals, A and B, which are phase-shifted by 90 degrees. By monitoring the signals, the direction and speed of the shaft can be determined.

Encoder in Digital Electronics

Linear Encoder: A linear encoder measures the position of a linear motion. It can be either absolute or incremental. Linear encoders are used in applications such as CNC machines, robotics, and printing presses.

Optical Encoder: An optical encoder uses a light source and a photoelectric sensor to measure the position of the shaft. The light source is placed on one side of the shaft, and the sensor is placed on the other side. As the shaft rotates, a pattern on a disk or a scale interrupts the light, which is detected by the sensor.

Magnetic Encoder: A magnetic encoder uses a magnet and a magnetic sensor to measure the position of the shaft. The magnet is placed on the shaft, and the sensor detects the changes in the magnetic field as the shaft rotates.

The Working Principle of an Encoder

The working principle of an encoder depends on its type, but in general, encoders function by converting physical motion into electrical signals that can be interpreted by a digital system.

In an incremental encoder, the encoder generates a series of pulses as the shaft rotates. These pulses are used to determine the relative position of the shaft, but they do not provide absolute position information. In contrast, absolute encoders provide a unique binary code or gray code output that corresponds to the absolute position of the shaft.

In an optical encoder, the light source generates light that is directed towards the rotating disk. As the disk rotates, the slots or marks on the disk interrupt the light, causing the light to be detected or not detected by the sensor. This creates a pattern of light and dark segments that can be interpreted as a series of electrical pulses.


In a magnetic encoder, the magnet on the shaft generates a magnetic field that is detected by the magnetic sensor. As the shaft rotates, the magnetic field changes, and the sensor generates electrical signals that correspond to the position of the shaft.

Linear encoders use a similar working principle to rotary encoders, but they measure linear motion rather than rotational motion. In a linear encoder, a scale with a series of marks is placed on a stationary object, and a sensor mounted on a moving object detects the marks as the object moves. This generates electrical signals that can be interpreted as the position or motion of the object.

Overall, encoders use various physical principles such as light, magnetic fields, or mechanical contact to generate electrical signals that correspond to the position or motion of a shaft or object. These signals can be used for control, monitoring, and feedback purposes in a wide range of digital electronics applications.

SEE ALSO: What is Solid State Relay (SSR)? How do Solid State Relays Work?

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