Micro-Thermostat

//Definitions for pins of Trinket 3.3V
  //AnalogWrite()
     #define AW_PB0 0
     #define AW_PB1 1
     #define AW_PB4 4    
  //AnalogRead()
     #define AR_PB2 1
     #define AR_PB3 3
     #define AR_PB4 2
  //Digital pins
     #define D_PB0 0
     #define D_PB1 1
     #define D_PB2 2
     #define D_PB3 3
     #define D_PB4 4

// variables and definitions
      //Important parameter, set to match environment
          const int dt = 500; // [ms] time constant in milliseconds (controller clock rate = 1/(dt/1000) [Hz])
          #define SetTemp 62.8 // [degC] set temperature in DegC
          #define MinTemp 20 // [degC] minimum expected temperature (needed for rescaling inputs)
          #define MaxTemp 65 // [degC] maximum allowed temperature, over which heater is turned off (needed for rescaling inputs)
          int SetTime = 1800; // [s] timer in seconds, if reached, running stops [Default: 1800]

      //I/O pins - don't edit unless replaced
          #define thermistorPin AR_PB4 //number of thermistor pin
          #define FETPin AW_PB1 //the number of the MOSFET pin
		  //#define LEDPin ? //the number of the LED pin

      //control parameters - editing not recommended     
          double K_P_ctrl = 15; //proportional gain
          double K_I_ctrl = 0; //integral gain (set to lower values i.e. 10^-3)
          double K_D_ctrl = 0; //derivative gain
          
// including headers
  #include <math.h>
  
//Inititalization
    //target temperature reached?
       bool bInRange = 0;

    //ticks per ms
       int TicksPerMS = floor(1000/dt);

    //Initialize PID variables:
       float previous_error = 0;
       float s_integral = 0;   

//Thermistor code - hard-coded constants for generic 10K NTC thermistor
    double Thermistor(int RawADC) {
      double Temp;
      Temp = log(10000.0*((1024.0/RawADC-1))); 
      Temp = 1 / (0.001129148 + (0.000234125 + (0.0000000876741 * Temp * Temp ))* Temp );
      Temp = Temp - 273.15;            // Convert Kelvin to Celcius
      return Temp;
    }

//PID controller code
    void Control_PID(double iTemp){
        
      //Overheat protection
          if(iTemp>MaxTemp){
            analogWrite(FETPin, 0);
            return;
          }
        
      //In range? If in range, do something (maybe turn on LED?)
          if((iTemp) >= SetTemp){
            if(bInRange==0){
              //TODO: add code what to do when in range
              //digitalWrite(LEDPin, HIGH); 
              bInRange=1;
            }
          }else{
            if(bInRange==1){
              //TODO: add code what to do when out of range 
              //digitalWrite(LEDPin, LOW); 
              bInRange=0;
            }
          }
          
        
        //PID subroutine
          float err = SetTemp - iTemp;
          s_integral += err*dt;
          float s_derivative = (err - previous_error)/dt;
          int U_in_ctrl = (K_P_ctrl*err + K_I_ctrl*s_integral + K_D_ctrl*s_derivative)/(MaxTemp-MinTemp)*255;
          previous_error = err;
                 
          
        // put voltage to output          
            if (U_in_ctrl<=255){
               if (U_in_ctrl > 0){
                  analogWrite(FETPin, U_in_ctrl);
               }           
               else
               {
                  analogWrite(FETPin, 1);
               }
            }
            else{
               analogWrite(FETPin,255);
            }                   
    }

void setup() {
    pinMode(FETPin, OUTPUT);
  
    //rescale timer according to dt
    SetTime = SetTime * TicksPerMS;    
}

void loop() { 
  //Take a temperature reading and display it 
    double Temp = double(Thermistor(analogRead(thermistorPin)));
              
  //Call controller algorithm 
    Control_PID(Temp); // call controller algorithm
    
  //Timer ticking (countdown)
    if (SetTime>0){
        SetTime--;
        // if zero reached
        if (SetTime==0){
          while(1) {
            //loop until disconnected - you might want to flash the LED or something...
            digitalWrite(FETPin, LOW);
            delay(dt);
          } 
        }
    }
    
   //wait dt before next cycle
      delay(dt); 
}