/********************************************************
   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 12

//Define Variables we'll be connecting to
double Setpoint, Input, Output;
int Vo;
float R1 = 10000;
float logR2, R2, T, rawdata;
float c1 = 1.009249522e-03, c2 = 2.378405444e-04, c3 = 2.019202697e-07;
float powervoltage=5;//define the power supply voltage.

const int ThermistorPin = A1;

//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 = 30;

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

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

void loop()
{
  
  Vo = analogRead(ThermistorPin);
  R2 = R1 * (1023.0 / (float)Vo - 1.0);
  logR2 = log(R2);
  T = (1.0 / (c1 + c2*logR2 + c3*logR2*logR2*logR2));
  T = T - 273.15;
  Input = T;
  myPID.Compute();

  /************************************************
     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);
  delay(500);
  Serial.println(T);
}