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Miniature Rotary Potentiometer: Does it exist?

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DigiTan

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I'm doing a project that involves detecting rotary motion. One type of sensor I'm considering is a potentiometer which would be connected to a rotating disc. The problem I'm having is that all the potentiometers I can find are limited to 1 full revolution, whereas I need one that can tolerate an endless number of revolutions--like a radio dial.

The tough part is that is has to be very small. Smaller than these **broken link removed** ones if possible. I've tried Digikey, Newark, and local shops, but I can't find one that meets the size requirement--possibly because it goes by another name. Where can I find this kind of component?

Also, would "rotary potentiometer" be the proper name for such a device, or does it go by some other description?
 
Mini pots aren't designed for what your trying to do. Most of them are designed for factory calibration and are only turned once - they are often reted at less than 100 turns before failure.

You should look into building a small optical encoder or magnetic encoder.

What sort of resolution do you need?
 
I need one that can tolerate an endless number of revolutions--like a radio dial.

well, all of the radio dials i've seen could sure be turned endlessly but not all of them would still work afterwards :)

you are looking for encoder.
 
Like mentioned, you want a rotory encoder of some kind. Is this disk only turning one direction? If so, it makes it real easy, and just some painted black marks with an IR led/sensor will work well. Otherwise you'll need 2 and a quadrature encoding scheme. I don't know if it will free up space by having the encoding part seperate or not, since we don't know enough about the project.
 
"Panic Mode" offered the CUI encoder and it's carried by Digi-Key -- if you can afford the $40 to $60 they want for it. Sounds like this is a simple project. If you don't need to know the direction of shaft turning, a simple "propeller" that slides through the slot of an optical interrupter (or a scratch-made version of one) would work for a simple project, two pulses per revolution. If you need directional information, you have to have a quadrature output from the encoder. You can make a simple "propeller" design by taking the back off a pot and soldering a shaft onto the back of the original shaft, maybe ripping out the "pot guts" first, and then adding the "propeller to the back. A simple "L" bracket over the pot bushing could hold the optical interrupter in proper position.

Oh, I forgot to mention (the reason for this edit) .... did you all realize that a stepper motor, the bigger the better, makes a not bad substitute for a quadrature encoder? Ground the center tap of one winding and use the other two leads as your quadrature output. Clip the output using diodes and send each through a comparator to square things up. Works great for nearly anything but REALLY SLOW shaft turns. If nothing else, it's a heck of a lot of fun to play with. I built a circuit that uses 74LS192 counters cascaded and a few extra gates and a flip-flop to cause the counter to run up or down depending on the direction of shaft turn. It was one of those "I wonder if a person could ...." kind of things that I'm always doing.

Dean
 
As far as resolution goes, the requirements are very loose. Anything offering at least 45º of resolution will work. The disc can spin in either direction at any time, at up to 5 rpm under normal conditions. I need two of these disc-and-sensor devices to fit in an enclosure about the size and shape of a hokey puck, so the "flatter" the sensor, the better.

I'm thinking of maybe using some optical or switch-contact scheme as an alternative. My biggest concerns with these methods is the noise generated when the optical interruptor begins to cast it's shadow on the receiver. If the disc stops in this position, I'm worried that it will cause the receiver's output to seesaw between between 'on' and 'off' states, and it'll create the illusion of a fast-moving disc. I'll have a microcontroller connected to receiver, so I'm sure theres some kind of software solution to the 'mid-state' noise issue.

Anyway, I'm sure it'll work out. I just wanted to know if any mini-pots could do this type of job.
 
There's no real noise there.

What you're asking about is called Hysteresis. The 'off' point is set lower than the 'on' point so that you don't get a stutter effect if the signal is a bit noisy.

You can get very small IR reflector sensors like a QRD1114 or even smaller. Paint reflective and non reflective bar on the disk and use it to check your position, or if it's easier for you, use a chopper wheel style encoder like Dean suggested.

If you need to measure direction as well, you'll need two sensors. If you look up quadrature encoder on google, or even on this forum, it'll tell you what it's all about. I think a microcontroller would be the best way to calculate this. There a bunch of article on how to hack wheel mouse encoders.
 
If you want it plain simple put an micro switch in and have an shaft that pushes it.If you want it silent this isent for you becod an micro switch makes a click(like a PC mouse click) wen its pushed or relesed

If your going to stack 2 IR rotation senstors close togeter put somting betwen it so the IR LED from the first one dosent fool the other one
 
You could also use a Hall effect sensor. This might be able to reveal the shaft's position rather than just RPM, albeit crudely and it may be subject to interference or calibration issues in regards to getting the position.
 
try 2SA-10 from www.gmw.com
i saw it in my sensors magazine from december 2004

**broken link removed**

**broken link removed**

**broken link removed**
 
the 2SA-10 is more expencive than QRD1114 and it's easier to implement with MCU so I would go with DirtyLude's suggestion.
you can always hack old computer mouse but QRD1114 is really affordable and simple to use (under $1) :)
 
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