linear encoder, optical?

I am considering ways to detect the movement and position of a “lazy susan” type turntable. Putting a rotary encoder on-axis is for various reasons impractical, so I’m thinking about some kind of optical linear encoder for the outer edge; if I were to decorate the edge of the turntable with a suitably patterned tape, I should be able to “read” it with a simple optical sensor.

It seems to me that somewhere in the 'verse, someone must be making linear edge encoding tape for just this purpose. But so far I haven’t found any off the shelf product in the Arduino, robotics, Maker realm. Does anyone know of such an animal? do I have to design my own? has anyone else tried to capture movement and absolute position of a rotating or linear slide by optical encoding one of the surfaces (moving or stationary) and mounting a sensor on the other?

I suppose in the worst case I could trigger Hall effect switches with a series of magnets, but that seems ugly compared to some kind of optical read head.

Maybe you can find old inkjet printers. I know HP used a transparent ribbon with dashes on it with a special optical chip reader, to measure the position of the ink-head. Maybe you can hack/re-use something like that.

I think this may answer part of my question

https://en.wikipedia.org/wiki/Rotary_en … ry_encoder

I’m not sure I really need absolute position. it would be nice, but perhaps not necessary; I could have a “reset” sensor when the turntable reaches dead-centre from either direction.

You will find that in most cases, encoders are either coupled axially to the motor on a through-shaft, or off-axis on the load (through gears, belts, etc). It’s certainly possible to do an edge-encoder (I think some DC turntables used to do this for speed control), but it’s likely to be a DIY effort.