PID Library

/********************************************************
 * PID Proportional on measurement Example
 * Setting the PID to use Proportional on measurement will 
 * make the output move more smoothly when the setpoint 
 * is changed.  In addition, it can eliminate overshoot
 * in certain processes like sous-vides.
 ********************************************************/

#include <PID_v1.h>

//Define Variables we'll be connecting to
double Setpoint, Input, Output;

//Specify the links and initial tuning parameters
PID myPID(&Input, &Output, &Setpoint,2,5,1,P_ON_M, DIRECT); //P_ON_M specifies that Proportional on Measurement be used
                                                            //P_ON_E (Proportional on Error) is the default behavior

void setup()
{
  //initialize the variables we're linked to
  Input = analogRead(0);
  Setpoint = 100;

  //turn the PID on
  myPID.SetMode(AUTOMATIC);
}

void loop()
{
  Input = analogRead(0);
  myPID.Compute();
  analogWrite(3,Output);
}