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Different type of potentiometer

edh329

Mar 28, 2014
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Mar 28, 2014
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I have come across a potentiometer which I have never seen before. What's different is that the wiper does not have an electrical connection. There still are three connections but the all connect to a little circuit board that has a shinny black material on the back. It appears that you can place any piece of metal on the black material to set the position of the pot. I measure a constant 3.3V between the red and black wires and the output based on the placement of the metal object on the black material can be measured on the blue wire. (see attached photo)

The device I have is from the torque control from a Dewalt cordless drill.

Has anyone else seen something like this or know anything more about these devices?

Ed
 

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edh329

Mar 28, 2014
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Mar 28, 2014
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I don't think its a hall effect device, hall effect use magnets this is just a metallic wiper with any electrical connection.
 

kpatz

Feb 24, 2014
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Feb 24, 2014
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Maybe it's a pressure sensing strip? What does the other side look like? Can you press on it with your finger instead of the metal piece and have the voltage/resistance change?
 

duke37

Jan 9, 2011
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Jan 9, 2011
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If it is a hall effect device, the magnet could be inside the detector and shunted by the wiper. For torque control perhaps it is measuring the magnetic field produced by the current into the drill.

Try a lump of iron and a lump of copper to see if there is any difference. A copper wiper could alter inductance.

There seem to be click stops, could these be pressing on a potetiometer track?
 

Kiwi

Jan 28, 2013
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Jan 28, 2013
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My guess would be hall effect.
Throttle position sensors in the automotive industry have usually been carbon track potentiometers, but with constant use and vibration etc they tended to wear out, or get flat spots. Some of the newer ones are now hall effect and "should never wear out".
 
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