I've been trying to build a cheap X-Y-Z table using mainly bits of old CD drives and printers I've got lying around. Since the printers already have a good single axis I would like to be able to, rather than having to buy a stepper motor and rebuild it, just repurpose the optical tabe the printer uses to keep track of the print head's position and keep the same DC motor. I've been able to extract the sensor the printer uses without damaging it or any part of the track, but I've been unable to find what the proper name of this sensor is, let alone documentation describing how to use it.
The sensor in question is in a black, plastic housing with a slit that the tape fits into. There are six pins on its underside that solder to the board, two of which come from something on top of the slit and four from something underneath. The black housing is labeled '6536' on top and '15' and 'DSO' underneath. My first guess is that the top is an LED while the bottom is a light sensor of some kind, but beyond basic checks (applying a weak current through the possible LED in either direction did not cause it to noticeably light up) I'm not sure how to get any more information out of it safely.
Answer
It sounds to me like an optical encoder, which looks something like this:
One side is an infrared emitter (which is why you can't see it--Infrared light is not visible to the naked eye) and the other side is the infrared receiver. The tape has very small stripes on it, through which light cannot pass. When this stripe blocks the IR light from the emitter, the receiver does not see it. When the tape continues to move, the clear portion of the tape eventually passes through. The light is then seen by the IR receiver, and the circuit can tell that the tape has moved.
I would expect the two-lead part to be the emitter and the 4-lead part to be the receiver.
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