ESP8266 NodeMCU: K-Type Thermocouple with MAX6675 Amplifier

Accurate temperature sensing is essential for many industrial, scientific, and DIY applications. When dealing with extreme temperatures, K-Type thermocouples are a go-to solution due to their wide range and reliability. When combined with the MAX6675 amplifier and the ESP8266 NodeMCU, you get a powerful and low-cost solution for wireless temperature monitoring.

In this guide, you’ll learn how to interface a K-Type thermocouple with a MAX6675 and the ESP8266 NodeMCU, build a simple local web server for displaying real-time temperature data, and explore options for data logging and IoT integration. For those unfamiliar with the MAX6675 module, check out the MAX6675 Technical Specifications. To write code for this setup, we’ll also be using the Adafruit MAX6675 Arduino Library.

Understanding the Components

ESP8266 NodeMCU

ESP8266 is a Wi-Fi-enabled microcontroller ideal for IoT projects
Features include GPIO, ADC, PWM, and I2C/SPI support
Easy to program using the Arduino IDE
Supports web server functionality

K-Type Thermocouple

Designed for high-temperature measurements
Temperature range: −200°C to +1350°C
Durable and cost-effective
Generates a small voltage proportional to temperature, which needs amplification

MAX6675 Thermocouple Amplifier

Converts thermocouple signal to readable digital data
Uses SPI communication protocol
Provides cold-junction compensation for accurate readings
Outputs temperature in 0.25°C increments

Wiring and Hardware Setup

Required Components

ESP8266 NodeMCU board
MAX6675 thermocouple amplifier module
K-Type thermocouple
Jumper wires
Breadboard (optional)
Power source (USB or battery)

Wiring Diagram

ESP8266 NodeMCU K-Type Thermocouple with MAX6675 Amplifier

VCC of MAX6675 → 3.3V on NodeMCU
GND of MAX6675 → GND on NodeMCU
SCK → D5
CS → D8
SO → D6

Tips

Ensure solid connections to avoid inconsistent readings
Use a proper power supply; unstable voltage can cause erratic sensor values

Software Configuration

Setting Up the Arduino IDE

Download and install Arduino IDE
Go to File > Preferences and add the ESP8266 board URL: http://arduino.esp8266.com/stable/package_esp8266com_index.json
Open Boards Manager, install “esp8266 by ESP8266 Community”
Select NodeMCU 1.0 (ESP-12E Module) from the board list

For deeper reference, visit the ESP8266 Arduino Core Guide

Installing the MAX6675 Library

Open Library Manager and search for MAX6675
Install “Adafruit MAX6675 Library”
This library handles all SPI communication and simplifies reading temperatures

Sample Code

#include "max6675.h"

int thermoDO = 12;
int thermoCS = 15;
int thermoCLK = 14;

MAX6675 thermocouple(thermoCLK, thermoCS, thermoDO);

void setup() {
  Serial.begin(9600);

  Serial.println("MAX6675 test");
  // wait for MAX chip to stabilize
  delay(500);
}

void loop() {
  // basic readout test, just print the current temp 
  
  Serial.print("C = "); 
  Serial.println(thermocouple.readCelsius());
  Serial.print("F = ");
  Serial.println(thermocouple.readFahrenheit());
 
  // For the MAX6675 to update, you must delay AT LEAST 250ms between reads!
  delay(1000);
}

Upload this sketch to your NodeMCU
Open the Serial Monitor to view temperature data in real time

Displaying Data on an OLED

You can enhance the visual experience by connecting a 0.96″ I2C OLED screen.

Integration Steps

Connect SDA to D1 and SCL to D2
Use the Adafruit_SSD1306 and Adafruit_GFX libraries
Display temperature readings dynamically alongside Serial Monitor

Creating a Web-Based Interface

Setting Up a Local Web Server

The ESP8266 can serve a basic HTML page using its Wi-Fi capability. Configure it as a web server to view temperature data from any browser on the same network.

#include "max6675.h"

int thermoDO = 12;
int thermoCS = 15;
int thermoCLK = 14;

MAX6675 thermocouple(thermoCLK, thermoCS, thermoDO);

void setup() {
  Serial.begin(9600);

  Serial.println("MAX6675 test");
  // wait for MAX chip to stabilize
  delay(500);
}

void loop() {
  // basic readout test, just print the current temp 
  
  Serial.print("C = "); 
  Serial.println(thermocouple.readCelsius());
  Serial.print("F = ");
  Serial.println(thermocouple.readFahrenheit());
 
  // For the MAX6675 to update, you must delay AT LEAST 250ms between reads!
  delay(1000);
}

Modify the code above by adding the thermocouple object and logic from previous examples
Access the web page by typing your NodeMCU’s IP address in your browser

Dynamic Updates with AJAX

Use JavaScript and AJAX to update only the temperature portion of the page
Reduces server load and improves user experience

Data Logging and IoT Integration

Logging temperature data is useful for analysis and monitoring over time.

SD Card Logging

Connect an SD card module via SPI
Log data with timestamps for later review

Cloud Platforms

Platforms like Blynk IoT Integration allow remote access
Display data on your smartphone using widgets and dashboards
Configure triggers for alerts if temperature exceeds thresholds

Applications and Use Cases

Industrial monitoring: Furnaces, kilns, and metalworking
Home automation: HVAC systems, smart thermostats
Scientific research: Chemical reactions, lab equipment monitoring

FAQs

How accurate is the MAX6675 with a K-Type thermocouple?
The module provides ±2°C accuracy for temperatures between 0°C and 700°C, which is sufficient for most non-critical applications.

Can the ESP8266 handle multiple thermocouples?
Yes, but it requires multiple MAX6675 modules and careful SPI chip-select management.

What is the maximum temperature range measurable?
With the K-Type thermocouple and MAX6675, you can measure from 0°C to 1024°C. The amplifier limits the top end, even though the thermocouple itself can go higher.

How to calibrate the thermocouple readings?
Calibration can be done by comparing readings to a known accurate thermometer and applying a correction factor in code.

Is it possible to use this setup without an internet connection?
Yes. The ESP8266 can host a web server on a local Wi-Fi network without internet access.

Conclusion

Using the ESP8266 NodeMCU with a K-Type thermocouple and MAX6675 amplifier is an effective way to build a wireless high-temperature monitoring system. This setup is compact, cost-efficient, and highly customizable, making it perfect for DIY makers, engineers, and hobbyists. With options for local display, web interface, and IoT connectivity, you can tailor it to a wide range of applications.

Experiment with the code, integrate it into your projects, and expand it with advanced features like cloud dashboards or voice assistants.