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Potentiometers causing problems when physically touched

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THuuN

New Member
Hello
My friends and I have encountered a problem that we have not seen before.
The circuit is essentially a light dimmer that works with no problems over multiple versions. Now with a new source/style of potentiometer, we find that the light will not turn on unless the potentiometer is suspended in OPEN AIR.

This is peculiar, no doubt. When the pot is touched with any sort of physical object, at best the signal weakens horribly, and most of the time it shuts the light off completely.

Any ideas as to why this happens??
Thanks so much
-Andrew
 
Broken lead (internally or externally), damaged wiper, spunky personality. I say donate it to science (tear it apart :-D ) and replace it with a new potentiometer.
 
Wow, cheap chinese potentiometer, how did you guess?

No seriously, I need you to answer that!
Is this an inherent problem with cheap Pots?? It seems ridiculous that grounding the potentiometer in any way can change the resistance value output..

We bought 'Case mounting Potentiometers' that do not work when mounting to a case??

Also, why not ask.. any recommendations on a reliable and affordable company for potentiometers??

Thanks again!
 
I wouldn't be to quick to jump on the Chinese bandwagon. Might be something subtle. What does the circuit look like?
 
Sounds like the assembly capacitance is causing problems. If your circuit is only using it as variable resistor (two leads). you might try moving the wiper connection to other terminal end of pot.
 
Well the problem occurs with any circuit board we use and any pot so it seems. Perhaps this is a design issue with the new components? The circuit is identical to our old one, except now using SMD components.

One potential problem is our unit's casing is anodized aluminum which is not conductive at the surface.
Could there be a problem with how the unit is Earth Grounded?? Although when we filed away the coating to create conductivity between the pot to earth.. it still doesnt work because the potentimeter is touching something...

If you really want, I will request permission to post the schematic.. but pot wiper goes to a comparator

here is a crude drawing of the parallel branch showing how the potentiometer is connected. Notice the wiper is only connected to the comparator.. but this worked fine in previous models and circuits.
Im quite convinced I need a different pot but if anyone knows more than me about Earth grounding, my ears are open for knowledge !!

[r1]
|
-
--> [MCP6541]
-
|
[R2]
|
=
(gnd)
 
One more thing to add that may be the key to some of you experts
The total resistance (outside leads) while the circuit is operating shows -45kohms
a NEGATIVE RESISTANCE
 
Hi THuuN,

are you sure you purchased a kind of pot which always will have wiper contact with the carbon film? There are pots made the way for "completely off" if turned to the left detent! (applied instead of a switch).

Your case is interesting!

Please submit a circuit diagram and a photo of your device.

Regards

Boncuk
 
One more thing to add that may be the key to some of you experts
The total resistance (outside leads) while the circuit is operating shows -45kohms
a NEGATIVE RESISTANCE

A multimeter measures resistance by applying a constant current (say 0.1mA) through the leads, and measuring the voltage. It then calculates the resistance using R=V/I. If the circuit is powered, then it measures weird voltage (V) values it doesn't expect, so weird resistance values come out.

Andrew
 
A multimeter measures resistance by applying a constant current (say 0.1mA) through the leads, and measuring the voltage. It then calculates the resistance using R=V/I. If the circuit is powered, then it measures weird voltage (V) values it doesn't expect, so weird resistance values come out.

Andrew

A German saying: "Wer viel mißt mißt viel Mist." :) translated "Who measures a lot measures lots of garbage." :)
 
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