Thursday, May 6, 2010

Motor Encoder Circuit

The circuit I ended up using for the motor rotary encoder is pretty simple. It's nothing original, I learned how basic IR LEDs and detectors can be wired up from the Society of Robots tutorials. Also see the one on sensor building.

I used the following parts from Mouser:

720-IRL81A : 880nm IR emitter
512-QSE113E3R0 : 0.25ma, 5v IR detector

The resistor values I used were determined by experimenting with a breadboard. I managed to fry one emitter in the process, but the results should work OK. I'm sure you could substitute similar values for almost all the components, perhaps saving a little bit of power.

My second sensor came out a lot nicer than the first, primarily because I just used Manhattan style construction from the start and had a reasonable idea on how to lay out the circuit pads after doing it once already.

Unfortunately my photo is horrible, but here is the second board getting it's smoke test in a prototype system. The IR LED is visible in the upper left, picked up by the camera sensor but normally invisible to the eye. The red LED on the right is driven by the end of a few feet of cable, which will eventually be monitored by the Arduino.

It worked fine so I bolted it down on the rear of the second motor and after fiddling with clearance a bit I button it up.

The motors were then re-mounted on the frame and tires installed. Next comes a bunch of mechanical work to mount the motor controller, fix the linkages on the motors that disengage the gear box, and secure the motor and battery wires.

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