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Do small cylindrical potentiometers exist? I'm creating an LED "pen" which will change color corresponding to the position of the twist of the pen. Imagine one of those pens that retract when you twist them. Instead of a pen tip, I would like to use that same motion to control a potentiometer. I haven't been able to find anything that could fit in a pen, or in that cylindrical package.

I guess, my actual question is, does something like this exist? Or an alternative that would have the same effect?

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    \$\begingroup\$ Cylindrical potentiometers are very common. The issue seems to be finding one small enough, not finding a cylindrical one. \$\endgroup\$ – Olin Lathrop Feb 8 '13 at 20:09
  • \$\begingroup\$ Are they really cylindrical though? I expect most are actually small-diameter disks inside elongated housings. There are probably trim pots small enough for this application, but I doubt they have the durability. \$\endgroup\$ – Chris Stratton Feb 8 '13 at 21:27
  • \$\begingroup\$ What about a small motor with an amplifier to boost the output signal? \$\endgroup\$ – Ignacio Vazquez-Abrams Sep 4 '13 at 13:56
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There are ceramic trimmer potentiometers available with a diagonal of 3.57 mm (Panasonic EVM2N) and up, that could be used for the purpose:

Ceramic Trimpot (from Digikey listing)

The trimpot could be mounted face-on to the back of the "LED pen", to provide the rotation sensing required.

Note that trimpots are designed for very few rotations, from a few hundred to a few thousand times at best.

An alternative if you are looking for durability, is to mount an analog omnidirectional Hall effect sensor such as Allegro A1326 along one edge in the fixed portion pen, and a small magnet on the rotating portion:

Allegro A1326

Such sensors provide a ratiometric voltage output for magnetic field strength, the polarity being indicated by voltage above and below the midway value of the supplied voltage.

Using this method, non-contact sensing of rotation is possible: As the magnet is rotated, field strength increases to a maximum for North, and then reduces to zero, and increases again to a maximum for South. The corresponding sensor output would be a somewhat sinusoidal voltage against rotation angle, simple to sense and use.

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  • \$\begingroup\$ Awesome, thanks for the example with the hall effect sensor! \$\endgroup\$ – az_ Feb 9 '13 at 6:43
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At least they existed... If you can access an old (20+) radio receiver or audio set you'll find them behind the volume knob. Metallic and plastic case, I remember. But they are big to stuff into a pen.... Maybe there is a nano size. I suggest you choose other method for example using a magnet and a magnetic sensor.

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There used to be slimline multi-turn (3 turn or 10 turn) pots, less than 10mm diameter. Haven't seen them around lately though...

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