Motor position feedback ideas.

I removed this lens module from an old CD drive. But sadly instead of the usual 4 wire stepper motor, it has a normal 2 wire motor and a few gears to move the lens. I now want a way to get position feedback from it, any ideas on how can i do this?

this lens module

Which lens module?

I suppose the old CD drive must have had some position feedback mechanism separate from the motor - if you can figure out how that worked perhaps you can use the same solution.

One similar to this, but with a normal motor rather than a stepper.

Thats what has shocked me! No feedback at all. I read somewhere that the feedback came from the actual CD it was reading.

Linear pot?

Hmmm, but that limits my movement. Can i get a liner pot that moves 2+ inch?

Could i use a Rotary encoder?

On a printer I opened up there was what I would describe as a "linear encoder". It was a long strip of plastic stretched tightly with very thin lines printed or etched on it. I presume as the print head moved a sensor would read the lines to know when it passed the next "position".

I have a similar drive with a brushed motor and also thought it had no feedback. But after examining it closer it seems to have a magnetic encoder.
You only show one side of your mechanism. Take a look and see if the other side looks like this one. If it does, the spoked wheel attached to the motor shaft has a ring magnet with hall sensors on the circuit board below it. I don’t have a connector to fit the white ribbon cable to verify this but when I find one I will try to verify if I’m correct.


I´m planning to use one of these CD lectors for a couple of ideas, so I will follow you guys :)

Hmmm, but that limits my movement. Can i get a liner pot that moves 2+ inch?

Yes, but not (easily) one that will work reliably with sustained continuous movement.