MAX31865 RTD Temperature Sensor

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Overview

The MAX31865-based RTD temperature sensor ADC supports 2, 3, and 4-wire PT100 probe configurations via SPI interface. RTD (Resistance Temperature Detectors) are precision resistance temperature sensors commonly used in industrial applications due to their excellent accuracy and long-term stability.

Specifications

Supports 2-wire, 3-wire, and 4-wire PT100 RTD configurations
15-bit ADC resolution
Overvoltage protection (±45V)
Built-in fault detection
21ms conversion time

Supported GPIO

Raspberry Pi 0~4
Raspberry Pi 5
BeagleBone Black/Green
Jetson Nano
FT232H, FT2232H, FT4232H

Commands

[INIT]

Initializes the module and configures RTD parameters.

Item	Type	Description
RTD Type	WRITE	Selects the RTD wiring configuration (2-wire, 3-wire, or 4-wire).

[READ_RTD]

Returns temperature, resistance, and ratio measurements.

Item	Type	Description
Ratio	READ	Ratio of current RTD resistance to reference resistance.
Resistance(Ohm)	READ	Current RTD resistance value.
Temperature(℃)	READ	Measured temperature.

[READ_FAULT]

Returns fault status and error codes.

Item	Type	Description
READ_FAULT	READ	Fault status message. Returns “No Error” when no faults are detected.

Example

Objective

Read temperature data from the sensor and display it on a dashboard gauge widget.

Parts

Part	Quantity
Raspberry Pi 4 *	1
MAX31865	1
RTD (PT100)	1

* Other compatible hardware may be used. See Supported GPIO for details.

Wiring

MAX31865-Raspberry Pi

Connect each MAX31865 pin to the corresponding GPIO pin as listed in each row below.

MAX31865	GPIO
VIN	3.3V
GND	GND
CLK	11 (SPI0 SCLK)
SDO	9 (SPI0 MISO)
SDI	10 (SPI0 MOSI)
CS	8 (SPI0 CE0)

MAX31865-PT100 RTD Probe Connection

• RTD polarity is not critical – positive and negative leads may be swapped.
• Either terminal of each polarity pair may be used for connection.

Jumper Connection

Complete Wiring Diagram (4-wire Configuration)

Project Link

References

Datasheet

Library

Adafruit Tutorial