PID_Peltier_Thermistor.ino

#include <math.h>

//目標の温度
double targetTemperature = 40.0;

//リレーを制御するピン
int enablePin = 2;


//サーミスタ関係
double T; //サーミスタの温度(T)
int currentTemperture = A0;//サーミスタのピン
const float DIVIDER = 10000.0; // 分圧抵抗10kΩ
const float T0 = 273.15;
const float R0 = 27700.0;
const float B = 3435.0;

int count = 0;
double input = 255.0;
double preinput = 255.0;
double deltainput = 0;
double e = 0;
double e1 = 0;
double e2 = 0;

double kp = 2.0; //比例ゲイン
double ki = 1.0; //積分ゲイン
double kd = 0.5; // 微分ゲイン

void setup() {
  Serial.begin(9600);
  pinMode(A0, INPUT); //A0番ピンを入力用に設定する
  pinMode(enablePin, OUTPUT);
  pinMode(thermistorPin, INPUT);

  digitalWrite(enablePin, HIGH);
}

void loop() {

  currentTemperture = getTemperature();

  Serial.print(targetTemperature);
  Serial.print(", ");
  Serial.println(currentTemperture);


  if (targetTemperature <= 24.0) {
    e = currentTemperture - targetTemperature;
  } else {
    e = targetTemperature - currentTemperture;
  }

  controlRelay();

  if (count == 0) {
    e1 = e;
    preinput = input;
  } else {
    e1 = e;
    e2 = e1;
    preinput = input;
  }

  count++;
  delay(1000);
}


double getTemperature() {
  float Aout =  float(analogRead(thermistorPin));
  //  Serial.println(Aout);
  float Rt = DIVIDER * Aout / (1024.0 - Aout);

  float result = calcTemp(Rt);
  return result;
}

float calcTemp(float Rt) {
  float T_bar = 1 / T0 + 1 / B * log(Rt / R0);
  return 1.0 / T_bar - 273.15;
}

void controlRelay() {
  if (count >= 2) {
    if (pid() > 255 / 2) {
      digitalWrite(enablePin, HIGH);
    } else {
      digitalWrite(enablePin, LOW);
    }
  }
}


int pid(void) {
  deltainput = kp * (e - e1) + ki * e + kd * ((e - e1) - (e1 - e2));
  input = preinput + deltainput;
  input = constrain(input, 0, 255);
  return input;
}