Overview

Temperature control is an essential requirement in many industrial, laboratory, and automation systems. This project demonstrates a simple, yet effective temperature controller built using an Arduino Uno, a MAX6675 Thermocouple Amplifier Module, a K-Type Thermocouple Sensor, and a 5V Relay Module.

The system continuously monitors temperature in real time and automatically controls a relay based on a user-defined temperature threshold. When the measured temperature reaches or exceeds the configured limit, the relay is activated. If the temperature falls below the threshold, the relay is automatically turned off.

For additional safety, the system also detects thermocouple connection failures and immediately disables the relay to prevent unintended operation.

This project can be used for heater control, temperature monitoring systems, industrial automation, incubators, ovens, furnaces, and various DIY temperature-controlled applications.

Features

• Real-time temperature monitoring
• Automatic relay control based on temperature threshold
• Supports K-Type thermocouple sensors
• Temperature display in Celsius and Fahrenheit
• Adjustable temperature threshold from software
• Thermocouple error detection
• Automatic relay shutdown on sensor failure
• Serial Monitor status reporting
• Simple and low-cost hardware design

Hardware Required

How the System Works

The K-Type thermocouple measures the surrounding temperature and sends a small voltage signal to the MAX6675 module. 

The MAX6675 performs: 

1.  Signal amplification
2.  Cold-junction compensation 
3.  Analog-to-digital conversion 

 The Arduino Uno reads the digital temperature data from the MAX6675 through SPI communication.

Every second, the system: 

1.Reads the temperature value. 
2. Converts the temperature to Celsius and Fahrenheit.
3. Displays the reading on the Serial Monitor.

4.Compares the temperature against the configured threshold. 

5. Controls the relay accordingly.

MAX6675 Connections

Relay Connections

System Operation

Temperature Measurement

The MAX6675 converts the thermocouple voltage into a digital temperature reading.

The Arduino reads:

• Temperature in Celsius
• Temperature in Fahrenheit

every second.

Example:

10.000 --> Temp: 27.50 °C | 81.50 °F
10.000 --> Relay: OFF

Relay Control Logic

The temperature threshold is defined in the code:

#define TEMP_THRESHOLD 30.0

Relay OFF Condition

Temperature < 30°C

Relay remains OFF.

Example:

 --> Temp:28 °C   --> Relay: OFF --> Temp: 31.75 °C   --> Relay: OFF

Relay ON Condition

Temperature ≥ 30°C

Relay turns ON.

on Serial Monior:

215.212 --> Temp: 31.50 °C  |  88.70 °F
215.214 --> Relay: ON
216.215 --> Temp: 31.75 °C  |  89.15 °F
216.217 --> Relay: ON

Thermocouple Error Detection

If the thermocouple becomes disconnected or communication fails:

Thermocouple ERROR! Check wiring.

The relay is immediately turned OFF for safety.

Software Setup

Required Library

Install the MAX6675 library through Arduino IDE Library Manager. or download on github

https://github.com/adafruit/MAX6675-library

Common library:

max6675

Upload Steps

1. Open Arduino IDE.
2. Install the MAX6675 library.
3. Connect your Arduino board.
4. Open the project sketch.
5. Select the correct board and COM port.
6. Click Upload.
7. Open Serial Monitor.
8. Set baud rate to:

9600

Adjusting Temperature Threshold

Modify the following line:

#define TEMP_THRESHOLD 30.0

Examples:

#define TEMP_THRESHOLD 50.0

Relay turns ON at 50°C.

#define TEMP_THRESHOLD 100.0

Relay turns ON at 100°C.

Serial Output on...