SparkFun: SoftPot Variable Potentiometer
Overview
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"); fflush(stdout); exit(1); } rewind(fp); //read value fgets(buf, 64, fp); //format for printing printf("The SoftPot was touched at %d\n", 100*atoi(buf)/4095); //close file pointer fclose(fp); return 0; }