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I've just got this problem: I have a potentiometer with resistance of 50k and i have an arduino nano which has an ATMega328 IC on it.

I attached the potentiometer normally: two pins for source and gnd and one pin going to the arduino nano's analog pin.

If i turn the knob slowly, the potentiometer increase its reading linearly and nicely. But if i were to turn the knob rapidly, say from medium to low, the potentiometer momentarily jumps up to the source voltage and return to its normal reading after 2 seconds or so. I'm suspecting that's because the arduino nano's analog pin attenuate the voltage so much and momentarily give me wrong readings. I checked ATMega328's datasheet and they have an internal resistance of around 60k which makes sense perfectly.

I'm using the potentiometer in an alarm clock to set the time precisely whenever i turn it and it always momentarily jumps to the highest reading or to the lowest reading. I can always wait a moment to make the values stable again but that takes too much time.

I could have simply lower the resistance of the potentiometer to around 10k or 5k but do you guys have another solution for this?

Thanks in advanced.

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  • \$\begingroup\$ Using a pot to set the time? Curious.... You may need to supply more information about how you are handling the ADC value too... that 2S thing sounds suspicious. \$\endgroup\$ – Trevor_G Jul 17 '17 at 19:41
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    \$\begingroup\$ This is most likely a software problem. It would take a huge amount of capacitance to cause the behavior you report over such a long time scale, so that is out. You need to show a minimal piece of code which illustrates the problem. \$\endgroup\$ – Chris Stratton Jul 17 '17 at 19:44
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Make a follower aka buffer with an op-amp. Connect the potentiometer's output to the \$V_{in}\$ of the op-amp and \$V_{out}\$ to the Arduino.

A follower/buffer is great at making weak signals strong.

enter image description here

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  • \$\begingroup\$ Can you provide some general-purpose buffer parts name so that i can look it up? I know that a simple npn transistor like 2n2222 would be enough to make an emitter follower but the voltage would drop 0.6V so do you recommend any other? \$\endgroup\$ – 157239n Jul 18 '17 at 5:34
  • \$\begingroup\$ All kinds of OP-amps can do the schematic above. If you need rail-to-rail (your output will swing from -supply to +supply => go from 0V to 5V) then you need this kind of setup if your op-amp doesn't do rail-to-rail. So a common LM358(doesn't do rail-to-rail) or a LM741(also doesn't do rail-to-rail) or any other op-amp that can be fed with 5 volts, cause that's what you're powering your arduino with, I assume, will work. \$\endgroup\$ – Harry Svensson Jul 18 '17 at 11:50

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