will be read-only starting December 31st, 2018. For more info pleae look at this Forum Post

PID Library

   PID RelayOutput Example
   Same as basic example, except that this time, the output
   is going to a digital pin which (we presume) is controlling
   a relay.  The pid is designed to output an analog value,
   but the relay can only be On/Off.

     To connect them together we use "time proportioning
   control"  Tt's essentially a really slow version of PWM.
   First we decide on a window size (5000mS say.) We then
   set the pid to adjust its output between 0 and that window
   size.  Lastly, we add some logic that translates the PID
   output into "Relay On Time" with the remainder of the
   window being "Relay Off Time"

#include <PID_v1.h>
#define RelayPin 6

//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, DIRECT);

int WindowSize = 5000;
unsigned long windowStartTime;
void setup()
  pinMode(RelayPin, OUTPUT);

  windowStartTime = millis();

  //initialize the variables we're linked to
  Setpoint = 100;

  //tell the PID to range between 0 and the full window size
  myPID.SetOutputLimits(0, WindowSize);

  //turn the PID on

void loop()
  Input = analogRead(0);

     turn the output pin on/off based on pid output
  unsigned long now = millis();
  if (now - windowStartTime > WindowSize)
  { //time to shift the Relay Window
    windowStartTime += WindowSize;
  if (Output > now - windowStartTime) digitalWrite(RelayPin, HIGH);
  else digitalWrite(RelayPin, LOW);