#include <Servo.h>
#include <PID_v1_bc.h>
#include <Wire.h>
#include <LiquidCrystal_I2C.h>

#define POT_PIN A0
#define RELAY_PIN 12

#define LCD_COLS 16
#define LCD_ROWS 2
#define LCD_ADDR 0x27

double setpoint, input, output;
double kp = 2.0, ki = 5.0, kd = 1.0; 
unsigned long prev_time;
int min_val = 0, max_val = 1023; 

Servo servo;
PID pid(&input, &output, &setpoint, kp, ki, kd, DIRECT);

LiquidCrystal_I2C lcd(LCD_ADDR, LCD_COLS, LCD_ROWS);

void setup() {

  Serial.begin(9600);

  servo.attach(9);

  pid.SetMode(AUTOMATIC);
  pid.SetOutputLimits(0, 255);

  lcd.init();
  lcd.backlight();
}

void loop() {

  input = analogRead(POT_PIN);
  input = map(input, min_val, max_val, 0, 255);

  unsigned long curr_time = millis();
  if (curr_time - prev_time > 100) {
    pid.Compute();
    prev_time = curr_time;
  }

  int servo_val = (int)output;
  if (servo_val > 0) {
    digitalWrite(RELAY_PIN, HIGH);
    servo.write(servo_val);
  } else {
    digitalWrite(RELAY_PIN, LOW);
  }

  setpoint = analogRead(POT_PIN);
  setpoint = map(setpoint, min_val, max_val, 0, 255);
  lcd.setCursor(0, 0);
  lcd.print("SP: ");
  lcd.print(setpoint);
  lcd.setCursor(0, 1);
  lcd.print("PV: ");
  lcd.print(input);
}