MAX31865 - Resistance Temperature Detector Amplifier

The MAX31865 device is a SPI interface Resistance Temperature Detector to Digital Converter.

Documentation

• MAX31865 datasheet

Usage

Important: make sure you properly setup the SPI pins especially for ESP32 before creating the SpiDevice, make sure you install the nanoFramework.Hardware.ESP32 nuget:

//////////////////////////////////////////////////////////////////////
// when connecting to an ESP32 device, need to configure the SPI GPIOs
// used for the bus
Configuration.SetPinFunction(21, DeviceFunction.SPI1_MOSI);
Configuration.SetPinFunction(22, DeviceFunction.SPI1_MISO);
Configuration.SetPinFunction(23, DeviceFunction.SPI1_CLOCK);
// Make sure as well you are using the right chip select

For other devices like STM32, please make sure you're using the preset pins for the SPI bus you want to use. The chip select can as well be pre setup.

SpiConnectionSettings settings = new(1, 42)
{
    ClockFrequency = Max31865.SpiClockFrequency,
    Mode = Max31865.SpiMode1,
    DataFlow = Max31865.SpiDataFlow
};

using SpiDevice device = SpiDevice.Create(settings);
using Max31865 sensor = new(device, PlatinumResistanceThermometerType.PT1000, ResistanceTemperatureDetectorWires.ThreeWire, ElectricResistance.FromOhms(4300));

while (true)
{
    Debug.WriteLine($"Temperature: {sensor.Temperature.DegreesCelsius} ℃");

    // wait for 2000ms
    Thread.Sleep(2000);
}

Note: You can use any PT100 or PT1000 temperature sensor which has 2/3/4 wires.

Hardware Required

• MAX31865
• Male/Female Jumper Wires

Circuit

The following fritzing diagram illustrates one way to wire up the MAX31865 Resistance Temperature Detector to Digital Converter with a MCU

• SDI - MOSI
• SDO - MISO
• CLK - SCLK
• CS - CE0
• VIN - 3V
• GND - GND

Known limitations

This version only performs the one shot temperature conversion and not the continuous temperature conversion.