J.F.Drew © 2000-2017

Projects by John F Drew Site map

Mobile menus


Gray coded optical encoders

Codechamp manufactures optical encoders, some of which have quite amazing resolution. They find uses in a wide range of devices from radars to helicopter turrets.


The device described on this page was a result of some work with Christer SM4FXR who has a 16 bit Gray coded device.

The secret to making the 16bit device work with my system is threefold:

  1. An interface to convert parallel input to serial output (this uses two 74HC165 chips)
  2. New hex file for the AZ/EL interface board to enable it to poll the 74HC165 and convert the received serial gray code into a variable holding a count from 0 to 65535 and then send this in serial form to the 'Shack Unit'.
  3. A modified version of the hex code for the shack unit so that it can deal the improved accuracy. This addition is in all versions of the Shack Unit code from Version 6.00 and above.

The interface:

Download this GIF of the circuit for the two 74HC165. Each chip converts 8 bits of the input from the encoder, the lowest significant bits from the first chip are couple to the serial input of the second chip to shuffle all 16 bits through to the AZ/EL unit.

SETUP: set menu items 25 and 26 to 16 bit.

The pin connections on the AZ/EL unit are:

The COA1E8C16 encoder (16 bit)

Photo right: The shift register system connected to the AZ/EL board.

Test setup on bench at SM4FXR

SM4FXR antenna system. A 3M dish for 1296MHz EME is being planned.

Here are the two files (one) and (two) of the specifications of the COA1E8C16 unit used by Christer. The manufacturer of the encoder is Codechamp S.A. in France.