How can I stop my potentiometers from smoking?

Other Miscellaneous
1

I recently purchased a 50mm softpot [(item #8680).

When I plug in my µC, smoke starts coming out of the SoftPot, and I get a cool looking scorch mark at the top of the sensor (pic below).

At the moment, I have it hooked up exactly like the [Fritzing diagram in this tutorial. However when I first tried this, I had the ground leg of the resistor and the ground leg of the softpot hooked up to the same ground pin on the arduino, which I assumed was an OK change to make— maybe that wasn’t a good assumption? I also initially had bad reading comprehension and used a 10 ohm resistor, could that have permanently fried the part?

Any help (even just letting me know I’m an idiot and broke it!) would be appreciated, thanks

Side note: When I try to choose American English instead of British English when signing up for this forum, I get stuck being redirected forever and can’t sign up

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](SoftPot Hookup Guide - SparkFun Learn)](SoftPot Membrane Potentiometer - 50mm - SEN-08680 - SparkFun Electronics)

2

Hi test1234,

I have to say I have never seen one of these potentiometers smoking like that. Can you take a few photos of your full circuit? My first guess is you may have had power and ground swapped somewhere. The low-value resistor and tying both grounds together should not have broken anything here. The resistor just pulls the signal line low so you do not have floating values when testing it.

3

Hello, and thanks for your post!

It sounds like you may have a wire crossed somewhere. You should have 5 volts and ground connected to the two outside terminals on the pot and the center terminal is your signal pin.

If you accidentally connect 5 volts to the center pin and ground to either of the outside pins, you will run into a situation where the pot is low resistance at one of the ends and that low resistance will draw enough current to cause the pot to get significantly hot. I’ve actually done the exact same thing so don’t feel bad!

It’s possible you may have damaged the pot to the point it doesn’t work correctly, but give the hookup below a try.

The 10k resistor in the diagram isn’t required, but will prevent the output value in the sketch from wandering when you’re not pressing on the potentiometer.

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The code below should work for you too.

/******************************************************************************
SoftPot_Example.ino
Example sketch for SparkFun's soft membrane potentiometer
  (https://www.sparkfun.com/products/8680)
Jim Lindblom @ SparkFun Electronics
April 28, 2016

- Connect the softpot's outside pins to 5V and GND (the outer pin with an arrow
indicator should be connected to GND). 
- Connect the middle pin to A0.

As the voltage output of the softpot changes, a line graph printed to the
serial monitor should match the wiper's position.

Development environment specifics:
Arduino 1.6.7
******************************************************************************/
const int SOFT_POT_PIN = A0; // Pin connected to softpot wiper

const int GRAPH_LENGTH = 40; // Length of line graph

void setup() 
{
  Serial.begin(9600);
  pinMode(SOFT_POT_PIN, INPUT);
}

void loop() 
{
  // Read in the soft pot's ADC value
  int softPotADC = analogRead(SOFT_POT_PIN);
  // Map the 0-1023 value to 0-40
  int softPotPosition = map(softPotADC, 0, 1023, 0, GRAPH_LENGTH);

  // Print a line graph:
  Serial.print("<"); // Starting end
  for (int i=0; i<GRAPH_LENGTH; i++)
  {
    if (i == softPotPosition) Serial.print("|");
    else Serial.print("-");
  }
  Serial.println("> (" + String(softPotADC) + ")");

  delay(500);
}
4

Thanks for your responses Mark and Chris— even if someone changed the original title of my post :slight_smile:

My setup looks just like your diagram, except I’m using one of your FCI clinchers to put the pot into my breadboard. Maybe you can already see where this is going… After prodding the clincher’s pins with a multimeter I measured a very low resistance between the ground and center pins. I checked a spare pot I bought, and did not see the same results. I opened up the clincher and sure enough two of the teeth that bite down were bent and touching. It’s my first time using one of these and clearly I wasn’t careful enough when I manhandled the cover shut. I pushed the pins apart, closed it back up, and plugged back into the redboard. Bad news: no matter what I do the value I get back is always 0. Good news: Nothing is smoking or catching fire.

So the part may be dead, but we solved the mystery. Thanks for pointing me in the right direction, and I’m glad I ordered a spare!