Interfacing MAX31855 Thermocouple Amplifier with Arduino

Introduction

Temperature measurement is a crucial aspect of many industrial and scientific applications. Thermocouples are widely used for temperature measurement due to their simplicity, durability, and wide temperature range. The MAX31855 thermocouple amplifier is a popular choice for interfacing thermocouples with microcontrollers. In this article, we will explore how to interface the MAX31855 thermocouple amplifier with Arduino, a popular open-source microcontroller platform.

What is MAX31855 Thermocouple Amplifier?

The MAX31855 is a thermocouple amplifier that is designed to provide accurate temperature measurements using thermocouples. It features a 14-bit ADC (analog-to-digital converter) that can convert the analog signal from the thermocouple into a digital signal that can be read by a microcontroller. The MAX31855 is also designed to compensate for cold junction temperature, which can affect the accuracy of the thermocouple readings.

Hardware Components

To interface MAX31855 Thermocouple Amplifier with Arduino, you’ll need the following hardware components to get started:

Components	Value	Qty
Arduino UNO	–	1
USB Cable Type A to B	–	1
DC Power for Arduino	–	1
Thermocouple Amplifier	MAX31855	1
Jumper Wires	–	1

MAX31855 Thermocouple Amplifier Pinout

Pin Number	Pin Function	Pin Function
1	GND	Ground
2	T-	Thermocouple input
3	T+	Thermocouple input
4	VCC	Power supply voltage
5	SCK	Serial clock input
6	CS#	Active low chip select. Set CS# low to enable the serial interface
7	SO	Serial-Data Output
8	DNC	Do Not Connect

Thermocouple Amplifier MAX31855 Circuit

Make connections according to the circuit diagram given below.

Wiring / Connections

Arduino	Thermocouple Amplifier
5V	VCC
GND	GND
D3	DO
D4	CS
D5	CLK

Installing Arduino IDE

First, you need to install Arduino IDE Software from its official website Arduino. Here is a simple step-by-step guide on “How to install Arduino IDE“.

Installing Libraries

Before you start uploading a code, download and unzip the following libraries at /Program Files(x86)/Arduino/Libraries (default), in order to use the sensor with the Arduino board. Here is a simple step-by-step guide on “How to Add Libraries in Arduino IDE“.

• SPI.h
• Adafruit_MAX31855.h

Code

Now copy the following code and upload it to Arduino IDE Software.

#include <SPI.h>
#include "Adafruit_MAX31855.h"
 
// Default connection is using software SPI, but comment and uncomment one of
// the two examples below to switch between software SPI and hardware SPI:
 
// Example creating a thermocouple instance with software SPI on any three
// digital IO pins.
#define MAXDO   3
#define MAXCS   4
#define MAXCLK  5
 
// initialize the Thermocouple
Adafruit_MAX31855 thermocouple(MAXCLK, MAXCS, MAXDO);
 
// Example creating a thermocouple instance with hardware SPI
// on a given CS pin.
//#define MAXCS   10
//Adafruit_MAX31855 thermocouple(MAXCS);
 
// Example creating a thermocouple instance with hardware SPI
// on SPI1 using specified CS pin.
//#define MAXCS   10
//Adafruit_MAX31855 thermocouple(MAXCS, SPI1);
 
void setup() {
  Serial.begin(9600);
 
  while (!Serial) delay(1); // wait for Serial on Leonardo/Zero, etc
 
  Serial.println("MAX31855 test");
  // wait for MAX chip to stabilize
  delay(500);
  Serial.print("Initializing sensor...");
  if (!thermocouple.begin()) {
    Serial.println("ERROR.");
    while (1) delay(10);
  }
 
  // OPTIONAL: Can configure fault checks as desired (default is ALL)
  // Multiple checks can be logically OR'd together.
  // thermocouple.setFaultChecks(MAX31855_FAULT_OPEN | MAX31855_FAULT_SHORT_VCC);  // short to GND fault is ignored
 
  Serial.println("DONE.");
}
 
void loop() {
  // basic readout test, just print the current temp
   Serial.print("Internal Temp = ");
   Serial.println(thermocouple.readInternal());
 
   double c = thermocouple.readCelsius();
   if (isnan(c)) {
     Serial.println("Thermocouple fault(s) detected!");
     uint8_t e = thermocouple.readError();
     if (e & MAX31855_FAULT_OPEN) Serial.println("FAULT: Thermocouple is open - no connections.");
     if (e & MAX31855_FAULT_SHORT_GND) Serial.println("FAULT: Thermocouple is short-circuited to GND.");
     if (e & MAX31855_FAULT_SHORT_VCC) Serial.println("FAULT: Thermocouple is short-circuited to VCC.");
   } else {
     Serial.print("C = ");
     Serial.println(c);
   }
   //Serial.print("F = ");
   //Serial.println(thermocouple.readFahrenheit());
 
   delay(1000);
}

Code Explanation

This Arduino code includes the necessary libraries to interface the MAX31855 thermocouple amplifier with the Arduino. It defines the connections between the MAX31855 and the Arduino using digital pins for software SPI, or hardware SPI. The code then initializes the thermocouple, waits for it to stabilize, and checks for any initialization errors. In the loop, the code reads the internal temperature and the temperature measured by the thermocouple, checks for any errors, and prints the temperature values to the serial monitor. The delay(1000) command creates a delay of 1 second before repeating the loop. This code provides a basic readout test for the MAX31855 thermocouple amplifier and can be used as a starting point for more advanced temperature sensing projects.

Applications

• Temperature sensing and control in industrial automation processes
• Temperature monitoring in automotive and aerospace applications
• Temperature measurement in laboratory and research settings
• Heating, ventilation, and air conditioning (HVAC) systems
• Temperature measurement in food processing and storage industries
• Temperature monitoring in power generation and distribution systems
• Temperature measurement in medical and healthcare applications
• Temperature measurement in scientific experiments and research
• In household appliances such as ovens, refrigerators, and water heaters

Conclusion.

Interfacing the MAX31855 with the Arduino is a simple and effective solution for accurately measuring temperature using thermocouples. By following the steps outlined in this article, you can quickly and easily integrate thermocouples into your Arduino projects. The MAX31855 thermocouple amplifier provides reliable and accurate temperature measurements, making it an excellent choice for a wide range of applications.