Anybody remember a linear optical pot? - diyAudio
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Old 2nd May 2012, 12:01 PM   #1
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Default Anybody remember a linear optical pot?

Some years ago I remember seeing a data sheet for a linear pot, like you'd find on an equalizer or mixing board. It was some kind of optical PSD (position sensitive detector) and was controlled by moving a light source up and down the active area. The claim to fame was that it could never get noisy or dirty or wear out. Does it still exist?
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Old 2nd May 2012, 11:49 PM   #2
Enzo is offline Enzo  United States
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Well, may not be what you want, but linear position sensors could be used that way. Google it. The ones I know are more like a plunger out the end of a body rather than the format of a slide pot as used in mixers. But under the panel, who cares.

But google up "optical fader" I suspect that will be what you are seeking.

Here is one:
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Old 3rd May 2012, 11:48 AM   #3
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Neat! "Fader" isn't part of my normal audio vocabulary so I didn't think to search on it. Though it's a neat device, I'm actually looking for a cheap non-contact measurement solution for a mechanical project. The thing I remember seeing is basically like the fader, but you have to supply your own light source to activate it. There are position sensitive diode detectors, but they're way expensive.
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Old 3rd May 2012, 01:41 PM   #4
Enzo is offline Enzo  United States
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What resolution do you need? You could go discrete - a common light source, even ambient, and a row of sensors, then some sort of light block on the moving part. Cover/uncover the sensors in a row, like LED VU meters in reverse.

Look at Morley guitar effect pedal units. They make a variety. They use the "Morley bulb". All that means is a small lamp - a 367 if I recall - (Yep. #367 MINIATURE BULB MIDGET FLANGE BASE, T1 3/4 SC MID FLG 10V .04A .08CP, #367, 367, #367 BULB, #367 MINIATURE, #367 LAMP, #367 MINIATURE LAMP, #367 MINIATURE LAMPS, #367 INDICATOR, EIKO# 49709) shining on a photocell. The pedal works moved a flexible piece of black fabric in between the lamp and the photocell. Non contact, very reliable, it worked, AT least until you needed a new lamp.

Scroll down a ways
Morley
to the picture just after the one of the bottom cover. On the right wall is the lamp, then the wide black fold of fabric connected to the gas pedal. The sensor is on the part with the two striped wires trailing left. The roll of flex fabric varies the light to the sensor. Note, ambient light would confuse this - the Morley only works with the bottom cover on.

Other systems come to mind where there was a light and a sensor looking at each other, and a bar with a V-shaped slot was moved between them. Depending upon position, the light went through a wider or narrower part of the V-slot, thus varying the light to the sensor.

So your moving thing could sport a wedge shaped part that progressively blocked more and more light to a sensor.

Some DOD/Digitech multiFX pedals have a pedal that moves a small clear plastic strip up and down through the gap in a photo coupler. The strip is actually printed with a gradated darkening. So the farther down you push the "gas pedal" the darker the part between light and sensor. And that controls the circuit.

SO there are three approaches to the same thing - moving baffle, varying gap, varying opacity - to change light impinging upon a sensor.


SO the row of sensors idea is kinda digital, while the othersw are continuously variable in an analog way. MAybe those suggest something easy to make.
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Old 3rd May 2012, 02:12 PM   #5
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Conrad: How about some sort of a hall sensor for mechanical measurement? Check out NVE spintronic GMR magnetic sensors isolators and MRAM they have some interesting parts and apnotes. E
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Old 4th May 2012, 04:45 AM   #6
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Thanks all- I'm familiar with about every way of modulating light and sensing; the pot thingy just would have made a particular job easier. I'm making my own using the ideas above.
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