---
active: false
tags: project
created: 2026-05-28 15:23
---
## Summary

Building an I2C temperature controller involves reading temperature from an I2C sensor (like an MCP9808 or DHT12) and using an Arduino to trigger a relay (for heaters/coolers) or adjust a fan.  Use the standard `<Wire.h>` library for communication and control relays based on your temperature thresholds. 

Here is a straightforward guide to get your project running.

🛠️ Hardware Requirements

- **Microcontroller:** Arduino Uno or Nano
- **I2C Temperature Sensor:** MCP9808 (High precision) or DHT12
- **I2C Display (Optional):** 16x2 LCD with I2C backpack (PCF8574)
- **Control Element:** 5V Relay module (to switch a fan or heater)
- **Misc:** Breadboard, jumper wires, and 4.7kΩ pull-up resistors (if not built into your sensor modules) 

🔌 Wiring the Components

Connect your I2C devices to the Arduino's I2C bus. You will share these lines between the sensor and the display.

- **VCC**  Arduino 
- **GND**  Arduino 
- **SDA** Arduino Analog Pin (or the dedicated pin on newer boards)
- **SCL** Arduino Analog Pin (or the dedicated pin on newer boards)
- **Relay Signal Pin** Arduino Digital Pin 

Before running this code, ensure you have installed the **Adafruit MCP9808 Library** and the **LiquidCrystal_I2C Library** via the Arduino IDE Library Manager (`Sketch > Include Library > Manage Libraries`).

```
#include <Wire.h>
#include <Adafruit_MCP9808.h>
#include <LiquidCrystal_I2C.h>

// Create sensor and display objects
Adafruit_MCP9808 tempsensor = Adafruit_MCP9808();
LiquidCrystal_I2C lcd(0x27, 16, 2); // Set the LCD address to 0x27 for a 16 chars and 2 line display

const int RELAY_PIN = 7;
const float TARGET_TEMP = 25.0; // Target temperature in Celsius
const float HYSTERESIS = 0.5;   // Prevents relay rapid switching (chattering)

void setup() {
  Serial.begin(9600);
  pinMode(RELAY_PIN, OUTPUT);
  digitalWrite(RELAY_PIN, HIGH); // Default to OFF (Relays are often active LOW)

  // Initialize I2C LCD
  lcd.init();                      
  lcd.backlight();
  lcd.setCursor(0, 0);
  lcd.print("I2C Temp Ctrl");

  // Initialize sensor
  if (!tempsensor.begin(0x18)) { // Default I2C address for MCP9808
    Serial.println("Couldn't find MCP9808!");
    while (1);
  }
  tempsensor.setResolution(3); // Set resolution to 0.0625°C
}

void loop() {
  tempsensor.wake();   // Wake up sensor
  float tempC = tempsensor.readTempC();
  tempsensor.shutdown(); // Shutdown to save power/reduce self-heating

  // Update Display
  lcd.setCursor(0, 1);
  lcd.print("Temp: ");
  lcd.print(tempC);
  lcd.print("C");

  // Temperature Control Logic
  if (tempC > (TARGET_TEMP + HYSTERESIS)) {
    digitalWrite(RELAY_PIN, LOW); // Turn ON cooling/heating
  } 
  else if (tempC < (TARGET_TEMP - HYSTERESIS)) {
    digitalWrite(RELAY_PIN, HIGH); // Turn OFF cooling/heating
  }

  delay(1000); // Read temperature every second
}
```


## Tasks


## References