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If you’ve reached here directly – please see:

https://dushyant.ahuja.ws/?p=740

I’ve modified the code to add the following:

1. Used the OneButton library so that the setpoint can be increased by clicking button and decreased by long clicking the button
2. Used the Timer library so that I don’t rely on delay – which was inaccurate
3. Change the logic for temperature such that the heater gets switched on if the temperature goes below the setpoint. Makes more sense as you don’t need the heater to be on at the setpoint. Also, reduces chances of the heater malfunctioning by switching on and off all the time
4. Used a similar logic for humidity – on when humidity is less than 50 and off when it is more than 60

#include "OneButton.h"
#include "EEPROM.h"
#include "Timer.h"

#define RELAY1 A1           // Connect humidifier to Relay1
#define RELAY2 A2           // Connect heater to Relay2
#define TEMP_SET 25         // Starting Temperature
#define MAX_TEMP 30         // Max Temperature
#define HUM_SET 40          // Threshold humidity
#define HUM_SET2 60
#define SWITCH_PIN A5       // Connect the switch between pin A5 and ground
#define CYCLE 10           //Time in minutes for each cycle

#include "LiquidCrystal.h"
#define LCD_RS 11           // * LCD RS pin to digital pin 12 - Green
#define LCD_EN 12           // * LCD Enable pin to digital pin 11 - Yellow
#define LCD_D4 5            // * LCD D4 pin to digital pin 5 - Blue
#define LCD_D5 6            // * LCD D5 pin to digital pin 6 - Blue
#define LCD_D6 7            // * LCD D6 pin to digital pin 7 - Blue
#define LCD_D7 8            // * LCD D7 pin to digital pin 8 - Blue

#include "dht11.h"
#define DHT11PIN 13

dht11 DHT11;
LiquidCrystal lcd(LCD_RS, LCD_EN, LCD_D4, LCD_D5, LCD_D6, LCD_D7);
int temp_set;
Timer t;
OneButton button1(SWITCH_PIN, true);

void setup() {
  pinMode(DHT11PIN, INPUT);
  pinMode(LCD_RS, OUTPUT);
  pinMode(LCD_EN, OUTPUT);
  pinMode(LCD_D4, OUTPUT);
  pinMode(LCD_D5, OUTPUT);
  pinMode(LCD_D6, OUTPUT);
  pinMode(LCD_D7, OUTPUT);
  pinMode(RELAY1, OUTPUT);
  pinMode(RELAY2, OUTPUT);
  lcd.begin(16, 2);
  Serial.begin(9600);
  if(EEPROM.read(0) >= MAX_TEMP+1){
    EEPROM.write(0,TEMP_SET);
    temp_set=TEMP_SET;
  }
  else {temp_set=EEPROM.read(0);}
  lcd.print("Setpoint: ");
  lcd.print(temp_set);            // Display the setpoint temperature for 2 sec
  delay(2000);
  checkTemp(0);
  t.every(60000*CYCLE,checkTemp,(void*)0);
  button1.attachClick(tempPlus);
  button1.attachPress(tempMinus);
}

void loop() {
  // put your main code here, to run repeatedly: 
  button1.tick();
  t.update();
}

void tempPlus(){
      Serial.println("Plus");
      temp_set++;
      if (temp_set > MAX_TEMP) temp_set = TEMP_SET; // Cycle between TEMP_SET and MAX_TEMP
      lcd.clear();
      lcd.print("Setpoint: ");
      lcd.print(temp_set);
      EEPROM.write(0,temp_set);
      delay(1000);
      checkTemp(0);
}

void tempMinus(){
      Serial.println("Minus");
      temp_set--;
      if (temp_set < TEMP_SET) temp_set = MAX_TEMP; // Cycle between TEMP_SET and MAX_TEMP
      lcd.clear();
      lcd.print("Setpoint: ");
      lcd.print(temp_set);
      EEPROM.write(0,temp_set);
      delay(2000);
      checkTemp(0);  
}

void checkTemp(void* context)
{
  int chk = DHT11.read(DHT11PIN);
  // Serial.print("Read sensor: ");
  switch (chk)
  {
    case DHTLIB_OK: 
               // Serial.println("OK"); 
                break;
    case DHTLIB_ERROR_CHECKSUM: 
               // Serial.println("Checksum error"); 
                break;
    case DHTLIB_ERROR_TIMEOUT: 
               // Serial.println("Time out error"); 
                break;
    default: 
                lcd.println("Unknown error"); 
                break;
  }

  lcd.setCursor(0, 0);
  Serial.println(DHT11.humidity); 
  lcd.print("Humidity: ");
  lcd.print((float)DHT11.humidity, 2);
  lcd.setCursor(0, 1);
  lcd.print("Temp: ");
  lcd.print((float)DHT11.temperature, 2);
  Serial.println(DHT11.temperature); 
  if(DHT11.humidity < HUM_SET2){      digitalWrite(RELAY1, HIGH);     Serial.println("H1");   }   if (DHT11.humidity > HUM_SET) {
    digitalWrite(RELAY1,LOW);
    Serial.println("H0");
  }
  if(DHT11.temperature < temp_set){      digitalWrite(RELAY2, HIGH);     Serial.println("T1");   }   if (DHT11.temperature > temp_set){
    digitalWrite(RELAY2,LOW);
    Serial.println("T0");
  }
}