Sitron Labs MAX31855 Arduino Library

Arduino library for interfacing with the Analog Devices MAX31855 thermocouple-to-digital converter.

Description

The MAX31855 is a cold-junction compensated thermocouple-to-digital converter. The MAX31855 is available in multiple variants, each designed for a specific thermocouple type (K, J, N, T, S, R, or E). This library provides a simple interface to read temperature data and diagnostic information from the device via SPI.

Installation

Arduino IDE

Install via the Arduino Library Manager by searching for "Sitron Labs MAX31855".

Alternatively, install manually:

1. Download or clone this repository
2. Place it in your Arduino libraries folder
3. Restart the Arduino IDE

PlatformIO

Install via the PlatformIO Library Manager by searching for "Sitron Labs MAX31855".

Alternatively, add the library manually to your platformio.ini file:

lib_deps = 
    https://github.com/sitronlabs/SitronLabs_Analog_MAX31855_Arduino_Library.git

Hardware Connections

Connect the MAX31855 to your Arduino using SPI:

• VCC → 3.3V (check your board's specifications)
• GND → GND
• SCK → SCLK (Serial Clock)
• CS → Any digital pin (configure in code)
• SO → MISO (Master In Slave Out)

Usage

#include <SPI.h>
#include <max31855.h>

// Create sensor object
max31855 sensor;

// Define chip select pin
const int CS_PIN = 10;

void setup() {
  Serial.begin(9600);
  
  // Initialize SPI
  SPI.begin();
  
  // Setup the MAX31855 (SPI instance, speed in Hz, CS pin)
  // Maximum SPI speed is 5MHz
  sensor.setup(SPI, 1000000, CS_PIN);
}

void loop() {
  float temp_thermocouple;
  float temp_internal;
  bool shorted_vcc;
  bool shorted_gnd;
  bool open_circuit;
  
  // Read temperature and diagnostics
  sensor.read(temp_thermocouple, temp_internal, shorted_vcc, shorted_gnd, open_circuit);
  
  // Check for faults
  if (open_circuit) {
    Serial.println("Error: Thermocouple open circuit");
  } else if (shorted_vcc) {
    Serial.println("Error: Thermocouple shorted to VCC");
  } else if (shorted_gnd) {
    Serial.println("Error: Thermocouple shorted to GND");
  } else {
    Serial.print("Thermocouple: ");
    Serial.print(temp_thermocouple);
    Serial.print(" C, Internal: ");
    Serial.print(temp_internal);
    Serial.println(" C");
  }
  
  delay(1000);
}

API Reference

setup(SPIClass &spi_library, const int spi_speed, const int pin_cs)

Initializes the MAX31855 sensor.

• spi_library: SPI instance to use (typically SPI)
• spi_speed: SPI clock speed in Hz (maximum 5MHz)
• pin_cs: Chip select pin number

Returns 0 on success, or -EINVAL if SPI speed exceeds 5MHz.

read(float &temperature_thermocouple_c, float &temperature_internal_c, bool &is_shorted_vcc, bool &is_shorted_gnd, bool &is_open)

Reads temperature data and diagnostic flags from the sensor.

• temperature_thermocouple_c: Output parameter for thermocouple temperature in Celsius (0.25°C resolution)
• temperature_internal_c: Output parameter for internal reference junction temperature in Celsius (0.0625°C resolution)
• is_shorted_vcc: Output parameter indicating if thermocouple is shorted to VCC
• is_shorted_gnd: Output parameter indicating if thermocouple is shorted to GND
• is_open: Output parameter indicating if thermocouple connection is open

Returns 0 on success.

Specifications

• Thermocouple temperature resolution: 0.25°C
• Internal temperature resolution: 0.0625°C
• Maximum SPI speed: 5MHz
• Supports K, J, N, T, S, R, and E type thermocouples (depending on MAX31855 variant used)