SparkFun: SoftPot Variable Potentiometer

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The softpot is a thin potentiometer that can be used by just touching along the strip. The following is an excerpt from the SparkFun web site: These are very thin variable potentiometers. By pressing on various positions along the strip, you vary the resistance.

Inputs and Outputs

The potentiometer has a variable resistance between 100 and 10,000 Ohms that changes linearly with location pressed. When either pin 1 or 3 is connected to ground and the other is connected to VCC the location of the touch can be calculated by reading the voltage on pin 2.

Bone Usage

Hook up pin 1 on the SoftPot to GNDA_ADC (pin 34) and pin 3 on the SoftPot to VDD_ADC(1.8V) (pin 32). Pin 2 on the SoftPot can be connected to any remaining AIN channels. This voltage can then be read as any normal analog in reading.

Sample C Code

This code will give a simple readout of the current position the SoftPot is being touched. AIN3, pin 37, is being used as the input.

/** Demonstrates simple usage of the SoftPot variable potentiometer

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char **argv, char **envp)
	FILE *fp;
	char buf[64];
	//open file
	fp = fopen("/sys/devices/platform/omap/tsc/ain3", "r");
	if(fp == NULL){
		printf("error with opening analog in file\n");
	//read value
	fgets(buf, 64, fp);
	//format for printing
	printf("The SoftPot was touched at %d%\n", 101*atoi(buf)/4095); //101 for 0-100
	//close file pointer
	return 0;