|
|
Shaft Encoder Board
 |
This page has technical details and photos of a shaft encoder board that I designed to be mounted onto a standard servo motor body so that the sensor can look at a black and white segmented encoder disk mounted to the wheel that is mounted to the servo. The board uses the Hammamatsu Photoreflector IC available from Acroname Robotics. http://www.acroname.com/robotics/parts/R64-P5587.html Click on the photo to see a larger view. |
 |
 |
| A wheel encoder disk like that above is made such that the black and white segments are equal in size and frequency. The photoreflector IC's output will then alternate between high and low as the wheel is turned and the varying black and white segments pass in front of the IR emitter/detector. | Here is a photo of the board artwork for board 2. There are 2 boards, each a mirror of the other to allow mounting on opposite sides of the bot. If the boards were not mirrored, the sensor would be positioned at different places and thus at a different point on the radius of the wheel. This would result in one sensor firing more often than the other. |
 |
The schematic is the same for either board. The mirroring effect is done only on the layout. This schematic is based on the data sheet for the Hammamatsu Photoreflector IC. See the link above for info at the acroname site. To make your own board, use the .pdf files below to transfer the artwork to the copper clad board using an iron on transfer, then etch the board. Be careful drilling as the holes for the Hammamatsu IC are very small and closely spaced (1.07 mm from center to center). Also note that there are 5 pins on this IC, 3 on one side and 2 on the other. |
In the photo above notice that I have scraped copper between the traces on the 3 pin side of the IC to avoid shorting. It is difficult to etch a board with such precision as to not get an unintentional short across those pins, so I made sure there was copper extending horizontally outward on both sides for good soldering. Use an exacto knife to be sure you have separation between the pins. Artwork files in PDF format click here for board 1 artwork ---------------------------- click here for board 2 artwork Schematic and layout files in Eagle format Side 1: schematic file ------ board file Side 2: schematic file ------ board file |
Here are some sample disks suitable for printing and framing.
%! Postscript utility for printing an encoder wheel gsave showpage |
