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360 degree Rotary Encoder Module

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About the Product

360 degree Rotary Encoder Module

The rotary encoder can count the number of pulses output in the forward and reverse directions by rotation, and the rotation count is not like the potentiometer. This rotation count is not limited. With the key on the rotary encoder, you can reset to the initial state, that is, counting from 0.


  • Operating voltage: 5V
  • Number of pulses: 20

Rotary Encoder Basics:

A rotary encoder has a fixed number of positions per revolution. These positions are easily felt as small “clicks” you turn the encoder.

On one side of the switch there are three pins. They are normally referred to as A, B and C.

Inside the encoder there are two switches. Once switch connects pin A to pin C and the other switch connects pin B to C.

In each encoder position, both switches are either opened or closed. Each click causes these switches to change states as follows:

  • If both switches are closed, turning the encoder either clockwise or counterclockwise one position will cause both switches to open
  • If both switches are open, turning the encoder either clockwise or counterclockwise one position will cause both switches to close.

The illustration below is representative of how the switch is constructed.

Rotary Encoder Representation

As you can see, the angular position of the A terminal and the B terminal is such that:

  • Rotating the switch clockwise will cause the switch connecting A and C to change states first.
  • Rotating the switch counterclockwise will cause the switch connecting B and C to change states first.

If we were to represent the opening an closing of the switches as wave forms, it would look something like this.

Rotary Encoder Phases

Essentially, determining which switch changed states first is how the direction of rotation is determined.

If A changed states first, the switch is rotating in a clockwise direction.

If B changed states first, the switch is rotating in a counter clockwise direction.


The pin outs for this rotary encoder are identified in the illustration below.

Keyes KY-040 Rotary Encoder Pin Outs

The module is designed so that a low is output when the switches are closed and a high when the switches are open.

The low is generated by placing a ground at Pin C and passing it to the CLK and DT pins when switches are closed.

The high is generated with a 5V supply input and pullup resistors, such that CLK and DT are both high when switches are open.

Not previously mentioned is the existence of of push button switch that is integral to the encoder. If you push on the shaft, a normally open switch will close. The feature is useful if you want to change switch function. For example, you may wish to have the ability to between coarse and fine adjustments.

Rotary Encoder Schematic

A schematic for this module is provided below. R2 and R3 in the schematic are pull up resistors.

Keyes KY-040 Rotary Encoder Module Schematic

Evaluation Circuit

Successfully implementing the Rotary Encoder into any project requires a clear understanding of everything that has been discussed thus far. If you’re still a little fuzzy, you may wish to throw together the evaluation circuit illustrated below:

Keyes KY-040 Rotary Encoder Evaluation Schematic

VERY SLOWLY rotate then encoder shaft both clockwise and counterclockwise. Notice which LEDs change state first with rotation.

Module Connection to the Arduino

Pretty straight forward… All you need to do is connect four wires to the module.

Keyes KY-040 Rotary Encoder Arduino Connections

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