Build an Incremental Encoder Quick Tester

How to build a portable incremental encoder tester.

Every once in while it’s nice to have a hand-held device that can be used to see quickly if encoder signals are present.  I designed and built a quick-tester that allows for fast interface to an encoder without having to drag out a power supply and oscilloscope.

The Quick-tester is an optical encoder tester that is powered by a 9V battery. An internal 5V regulator drops the voltage to 5V, as two of the connections are power connections for the optical encoder.

Current limiting resistors are wired in to red LEDs.   The LED’s illuminate when the optical encoder signals are High.  By rotating the base by hand we can see if a channel is dead or even improperly phased.

Here is the schematic for the Optical Encoder Quick-Tester

Things the Quick Tester can tell you:

Which channels are working.

The LED’s should rapidly blink on and off while the optical encoder hub is slowly rotated. Keep in mind that turning the hub too fast will make the LED’s switch on and off quickly and cause them to appear to be continuously illuminated.

Proper phasing

When channel A is illuminated, channel A- should be dark and vice versa. If both lights are on or off at the same time, there is a problem with the encoder.

If A leads B, or B leads A

Rotate the encoder shaft slowly until both A and B are low (off), then look for the next high channel, that channel is the leading channel for that direction of rotation.

Location of the index pulse

It can be easy to fly right past an index pulse, particularly on higher line count encoders, but the Quick tester can tell you precisely when the index pulse occurs. This can be handy for mechanically timing the optical encoder to a real world position.

Other things to note:

If you have an optical encoder with  open collector outputs, the Quick-tester’s LED’s will not illuminate unless you use pull up resistors between each channel and the positive supply of the Quick Tester.

If all lights are on, you have probably lost the signal ground connection to the Quick tester.

The Quick tester is set up to look at six channels at a time, so it is likely you will be looking at only incremental channel or only commutation channels.

For more information on encoders, go to

Jim can be reached at


About Quantum Devices Inc.
Quantum Devices, Inc. (QDI) Barneveld, WI, was established as a Wisconsin corporation in October 1989, as an outgrowth of activities in the general area of optoelectronics. The main goal of QDI is to provide customers with a complete source for all stages of product design and development, starting from concept to a marketable commodity. These products include application specific Silicon Photodiodes, Optical Encoders and Light Emitting Diodes (LED) for commercial, industrial and medical applications. QDI's photodiodes and LED's are used in instrumentation for photosynthesis and photobiological research, biomedical and medical instrumentation for measuring blood sugar levels (glucometer), oxyhemoglobin and pulse rate (pulse oxymeter). One of the most dramatic products developed at QDI was the application of LED lighting systems for use as the light source for Photodynamic Therapy (PDT). Sales of QDI products include both domestic and international markets. Quality and reliability are very important concepts in maintaining our company wide commitment to overall product performance. Quality simply means continuous process improvement. We are committed to continually increasing our product excellence through increased quality and reliability. Quantum Devices, Inc. is ISO 9001 certified and the ISO Standard will provide the guidance for the vital function of maintaining our commitment to constantly improve our product quality. Quantum Devices is now proud to introduce it's new line of rotary encoders. Incorporating QDI's patented sensor technology, our QPhase™ Family of Encoders feature high resolution, increased frequency response and superior reliability over temperature (0 to 120 degrees C). QDI incremental and absolute encoders set a new standard and are backed by a 2 year factory warranty. We invite you to request an evaluation unit, additional information or price quotations. Mission Statement Quantum Devices is dedicated to the principle that light provides the power for all life on earth. We believe the quality, delivery and control of light is essential to the wellness of man and his advancement into the future.

4 Responses to Build an Incremental Encoder Quick Tester

  1. Bob Harris says:

    Thank you for publishing encoder tester drawing, do you have a parts list where I can purchase the parts to build it.

    • Thanks for stopping by Bob,

      I mostly used parts we had lying around but here is a list to get you started. These items can be purchased through Digikey in quantities as low as one

      220 Ohm Resistor, CF14JT220RCT-ND, $.08 Each
      Red LED, 516-1381-ND, $.67 Each
      9V Battery Clip , 377-1549-ND, $1.20 Each
      +5V Voltage Regulator, LM7805ACT-ND, $.60 Each
      Rocker Switch, CH760-ND, $1.29 Each
      Perf Board, V2025-ND, $6,26
      Serpac Enclosure (Project Box),SR211G-ND, $4.98 Each


  2. hossam says:

    Thank you for publishing encoder tester drawing, do you have a parts list where I can purchase the parts to build it. Thank you

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