Rotary Encoder Basics and Types: Understanding Rotary Sensors

This article covers rotary sensor basics and rotary sensor types. The encoder which senses angular position is known as a rotary encoder or sensor. The working of this rotary encoder is also described with the output timing diagrams.

What is a Rotary Sensor or Rotary Encoder?

Introduction: It is a type of position sensor used to determine the angular position of a rotating shaft.

It generates an electrical signal, which is either analog or digital. The electrical output is sensed or used by a micro-controller board or Arduino to perform the desired action.

Figure-1 depicts a Keyes rotary encoder, which provides an indication of the knob position and its direction. It is used for stepper and/or servo motor controls.

Following are the mappings between various pins on the rotary encoder:

• CLK - Encoder Pin-A
• DT - Encoder Pin-B
• SW - NO Pushbutton Switch
• + is connected to 5V Supply
• GND - Encoder Pin-C

Rotary Sensor Types | Rotary Encoder Types

• The rotary encoder or sensor is classified according to the output signal or sensing technology.
• Based on the output signal, rotary sensors are of two types: incremental and absolute. An incremental type of encoder is also known as a quadrature encoder or relative rotary encoder.
• Based on sensing technology, rotary sensors are of three types: magnetic, optical, and laser.

Rotary Sensor Working

The following section describes the working of a rotary sensor:

• Figure-1 depicts a circular disk with evenly spaced contact zones, which are connected to a common pin “C”. There are two contact pins designated as “Output-A” and “Output-B”.

• When the disc rotates, pins A and B come into contact with the evenly spaced contact zones, and two square wave output pulses are generated.

• Either output-A or output-B is used to determine angular or rotational position.

• But to determine direction, both the output signals and their signal transitions i.e. high to low (H-L) and low to high (L-H) are monitored or measured. As shown for clockwise movement of the shaft, output-A leads output-B in both H-L and L-H transitions.

• Similarly, anti-clockwise rotational movement can also be measured or tracked.