Optical pulse encoder thingies

[Antimon]

Say I would like to make my own endlessly spinning mod wheel - like a classic mod wheel on a synth keyboard only without stops at max and min within an interval.

I don't have a clue how to make stuff, but if I concentrate on getting reading the value from the wheel - my idea is to have a one dimensional optical reader similar to the two dimensional ones you find in optical mice or trackballs. So basically whatever light emitter and detector and logic is needed to detect movement and transform it into pulse data that I can decode and have increment or decrement a single variable.

Is such a thing available (detector+light+logic -> pulse thingie) for purchase somewhere?

Once I have that I figure I could start thinking about how to make a wheel and spinning axis out of scrap or something...

Attaching an image that might clarify what I mean.

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[DrJustice]

I'm not sure what you mean by "one dimensional optical reader", as opposed to the usual quadrature encoding/decoding. You do mention mice and trackballs, and one method is to just grab an old one and use the slotted wheels and detectors. You could even use the mouse electronics as it is and just read the PS2 or USB serial data. Those optical detectors can be also bought at most well stocked component suppliers too (Mouser, Digikey, maybe ELFA...)

Complete quadrature encoder/decoder assemblies of various types can be bought - they're used all over the place in various industrial applications. I once had somewhat of an overview of this, but my references are in an old stowed away laptop. I'm sure you'll be able to google your way to the info.

Here's a good reference on quadrature decoding: fpga4fun, Quadrature Decoder.

DJ
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[Antimon]

Now I know the term "quadrature". Is that term also used for e.g. mice without moving parts, where you just see a red light underneath? Because that's the kind I'm interested in...

I mentioned one dimension as opposed to the two dimensions that are the domain of e.g. mice. A wheel will only spin along one axis.

Thanks for the info and link!

[DrJustice]

Ah, I got you - the two dimensions of the mouse movement...

Optical mice use an image sensor to take successive images of the surface, then a DSP compares the images and determines the direction and distance of the movement. The purpose of the LED is just to illuminate the surface.

As it happens, SparkFun (very cool shop fro DIY gadgetry) sell an optical mouse sensor. It does all the hard work and has a serial port for readout of the movement data. Perhaps a usable solution for your project?

DJ

Edit: typo
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[Antimon]

That SparkFun thing looks very interesting, thanks!

Maybe I should clarify that it's all about this project that I daydream about once in a while:

http://electro-music.com/forum/post-296127.html#296127

[DrJustice]

Right, I remember that one Should be very doable. A few rollerblade wheels, or something, a handfull of those optical mouse sensors, a microcontroller - and Bob's your uncle.

DJ
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[Antimon]

Hmm... I might just try to get one of those sensors, just to see how it works.

The dream stays alive!

[BobTheDog]

Why not just use a load of smooth endless encoders, mount the wheels on the encoder shafts?

[Antimon]

I wonder how smoothly you can get optical encoder shafts to turn. I would like to be able to set the wheel in motion so it will keep spinning for a while or until I stop it with my hands.

Do you know some particular encoder make that's smoother than others Andy?

[DrJustice]

One of the attractive features of using an optical mouse sensor is that you will get a controller with a very high resolution. The affordable consumer type rotary encoders doesn't have a lot of resolution, typically something like 24 or 32 steps per revolution. You can get very high resolution rotary encoders, but at a price - e.g. like this one with 80000 cycles per revolution.

DJ
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