Optical digital incremental encoder

In this article we will explain the basic principles of how optical digital increment encoder works. Digital incremental encoder is used for measuring speed rotation and position of a motor shaft. In our tutorial we will present HEDL 5540 digital incremental encoder designed and manufactured by MAXON company.

Operating principles of optical digital increment encoder

This type of encoder is usually mounted on motors. More about DC motors you can find in our article: Basic characteristics and mathematical model of DC motors. This encoder is based on the optical principle and is suitable for positioning tasks. It has the ability to determine the direction of rotation and the speed of the shaft rotation.
The encoder in Image 1 sends the light from the LEDs through a finely cut wheel firmly connected to the engine motor. Receivers (phototransistors) convert the light and dark signals into the corresponding electric rectangular impulses. This signal is amplified and sent to processing. This type of encoder is characterized by a large number of pulses at the output. It has the capability of the index channels and the possibility of line control. HEDL5540 occupies a large space on the motor.

Image 1. Operating principle of the HEDL 5540 encoder

The HEDL 5540 encoder gives 500 pulses per revolution per circle, i.e. one impulse gets on each 0.72 degrees. If the transmission gearbox is not 1:1 it also should be take into account on the output shaft, the angle is made to obtain one pulse at the encoder output.

Encoder output signals

There are 2 channels (A and B) and index channel I Image 2, as well as all channels in the complementary form. Channels A and B are phase-shifted, so their comparison can determine the direction of rotation of the rotor. The initial impulse (index channel I) is used as a reference in determining the angle of the rotor, but these encoder properties are not used in the tested drive module.

Image 2. HEDL 5540 encoder output timing diagram

MAXON HEDL 5540 encoder

The HEDL 5540 encoder catalog information is provided on an maxonmotor.com site: HEDL 5540
Image 3 shows the HEDL 5540 encoder.

Image 3. The HEDL 5540 encoder

Image 4 shows pinout on the IDC10 connector at the output of the HEDL 5540 encoder. Connector IDC10 (DIN-41651) has grid 2.54mm (01.inch).

Image 4. The HEDL 5540 encoder pinout

Pin function on the output connector are:

1 – N.C.
2 – Vcc (+5V)
3- GND
4 – N.C.
5 – A (Inverted Signal)
6 – A
7 – B (Inverted Signal)
8 – B
9 – I (Index) (Inverted Signal)
10 – I (Index)

Image 5 presents the dimensions of the HEDL 5540 encoder.

Image 5. The dimensions of the HEDL 5540 encoder

In our article “DC Motors – voltage, current, speed, power, losses and torque relationships” you can find out relationship between electrical sizes of a DC motors.

More about DC motor module and DC motor driver you can read in our tutorials: DC motors – module for motion of autonomous robot for EUROBOT competition and DC motors – driver for motion of an autonomous robot.

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Tutorials in the category: DC motors and drivers

  • DC motors – Basic characteristics and mathematical model
  • DC Motors – current, voltage, speed, power, losses and torque relationships
  • DC motors – driver for motion of an autonomous robot
  • DC motors – module for motion of autonomous robot for EUROBOT competition
  • Optical digital incremental encoder