In this instructable I'll show you how to make some really small encoders for your robot's DC motors. The sensors that are used in this instructable are Vishay's TCUT1300 IR Transmissive Sensor with photo-transistor output. Following the sensor's datasheet I designed a small board (10x8mm) that can fit in small spaces. Sometimes space is not the most available thing in a robot.
The board was designed to use 1/4W resistors and the wires would fit together in the holes with the resistor pins. However, since I had little space and some salvaged SMD resistors around, I ended up using those and the wires were soldered in the resistor's holes.
The schematic is really simple. It follows the typical application circuit from the datasheet. It uses a 220 ohm resistor to make a current of approximately 0.16mA circulating on the emitting LED and a 10K resistor between the output's photo-transistor emitter and GND. The output is in the signal R_TO_GND shown in the schematic.
I used my first CNC, TheMaker1, to route the PCB. Soldering the TCUT1300 is not easy but can be done with some patience and a thin-tipped soldering iron. To make it easier, I advise you to put some solder in the PCB before placing the TCUT1300. Then, place it on the board and heat the PCB tracks from the side until the solder below the component melts.
In the pictures area you'll be able to see of the assembled PCB and the Encoder mounted in some motors together with the encoder wheel.
The encoder wheel that I used was generated from a postscript file that can be tweaked to generate the encoder wheel with the specifications that you desire: outer diameter, double tracks, number of segments, phase difference, segment width, shaft diameter, etc. It can be found on Thinginverse here or directly download it using this link. Then use a text editor to edit the parameters that you'll find in the first 50 lines. They are properly commented, so they should be easy to understand.
You can download the Kicad files here.
For more information and higher quality pics see the original post here: http://www.thebitbangtheory.com/2013/05/tiny-encoders-dc-motors/
For other projects visit my blog: http://www.thebitbangtheory..com
This instructable was submited to the Epilog Laser Challenge. Please vote for it! :) If I win I'll use the Zing to cut and engrave the parts of the body of the robot that I'm making :)