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Absolute Binary Rotary Encoder



The Absolute Binary Rotary Encoder is a mechanical encoder capable of rotating a full 360° in both the clockwise and counterclockwise directions without limits. This device can also relate its current position relative to one of sixteen points on the encoder. The Absolute Binary Rotary Encoder is compatible with most microcontrollers including the Parallax BASIC Stamp 2 and Propeller as well as with the popular Arduino.

This product used to be labeled as Parallax under stock code 27804. It is currently sold labeled as SimplyTronics under stock code ST-00002 with the same functionality and specifications.

ST-00002-front 1280x1280.JPG

Product Features

  • Full 360° rotation with 16-position feedback
  • 6-pin DIP module is ready for breadboard or through-hole projects
  • Built-in 10 kΩ pull-down resistors on each output pin

Technical Details

  • Power requirements: Supply voltage = output signal voltage. Set supply voltage for compatibility with your microcontroller’s inputs.
  • Communication: 4-pin parallel binary output
  • Operating temperature: 32 to 158 °F (0 to 70 °C)
  • Dimensions: 0.80 x 0.75 x 0.73 in (20.32 x 19.05 x 18.67 mm)

Applications Ideas

  • Multi-Positional Selection Switch
  • Position and Motion Control
  • Temperature Adjustment
  • Volume Control

Pin Definitions

Pin Symbol Type Function
1 A Output Bit 0 of binary output
2 5V Power Supply Voltage 3.3-5 V
3 B Output Bit 1 of binary output
4 D Output Bit 3 of binary output
5 GND Ground Ground (0V)
6 C Output Bit 2 of binary output

Note: You can turn the encoder PCB upside down to look at the pin labels included in the bottom silkscreen. Although pin 2 is labeled 5V you can use a voltage compatible with your microcontroller working voltage, between 3.3 and 5 V.

Connection Diagram

The figure below depicts the connection diagram to be used with the included example BASIC Stamp and Propeller programs. The same connection can be used with most microcontrollers.


Note: Additional 220 Ω resistors may also be placed in series between the Absolute Binary Rotary Encoder and the microcontroller I/O pins to prevent potential I/O pin damage from accidental code errors.

Theory of Operation

The position of the Absolute Binary Rotary Encoder can be determined by monitoring the input states of pins A, B, C, and D. The sequence of these four states produces a standard binary count for each absolute position on the encoder. The table below lists the binary sequence for each decimal position:

D C B A Position
0 0 0 0 0
0 0 0 1 1
0 0 1 0 2
0 0 1 1 3
0 1 0 0 4
0 1 0 1 5
0 1 1 0 6
0 1 1 1 7
1 0 0 0 8
1 0 0 1 9
1 0 1 0 A
1 0 1 1 B
1 1 0 0 C
1 1 0 1 D
1 1 1 0 E
1 1 1 1 F

A Note about Binary Encoding

In cases where more than one bit is changed between positions, it is possible for the output of the Absolute Binary Rotary Encoder to fluctuate. For example, the change from position 7 to 8 results in a binary change of all 4 bits, from “0111” to “1000.” When this happens, it’s possible for certain bits to change before others, so you may see a brief oscillation in position. While this is perfectly normal for this type of encoding, caution should be exercised when using in applications that may require a higher level of accuracy.

Resources and Downloads


This program displays the current position of the Rotary Encoder using the Debug Terminal built in to the BASIC Stamp Editor.


This program displays the current position of the Absolute Binary Rotary Encoder using the Parallax Serial Terminal.