MAX31865 PT100 RTD Temperature Sensor Module: Complete Guide with Arduino

The MAX31865 is a dedicated RTD-to-digital converter designed to simplify the use of PT100 and PT1000 platinum RTD sensors. It features a high-resolution 15-bit ADC, built-in fault detection, and an SPI interface, allowing microcontrollers such as Arduino, ESP32, STM32, and Raspberry Pi to read precise temperature data with minimal external circuitry. The chip also supports 2-wire, 3-wire, and 4-wire RTD configurations, making it suitable for a wide range of applications.

In this guide, you'll learn everything you need to know about the MAX 31865 PT100 Temperature Sensor Module, including its working principle, technical specifications, key features, pinout, Arduino wiring and code example, practical applications, datasheet information, and answers to frequently asked questions. Whether you're building a DIY electronics project or designing a professional temperature measurement system, this guide will help you get started with the MAX 31865.

1. What is the MAX31865 PT100 Temperature Sensor Module?

2. Technical Specifications

3. Key Features

4. MAX31865 Module Pinout

5. Arduino Wiring

6. Application

7. Frequently Asked Questions [FAQ]

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What is the MAX31865 PT100 Temperature Sensor Module?

The MAX 31865 PT100 Temperature Sensor Module is a high-precision RTD (Resistance Temperature Detector) interface designed to convert the resistance of platinum RTD sensors into digital temperature data. Optimized for PT100 and PT1000 sensors, the MAX 31865 integrates a 15-bit Delta-Sigma ADC, precision bias circuitry, and an SPI communication interface, allowing microcontrollers to read accurate temperature measurements with minimal external components.

Platinum RTDs are widely recognized for their excellent accuracy, long-term stability, and repeatability. A PT100 sensor has a resistance of 100Ω at 0°C, and its resistance changes predictably as the temperature varies. Compared with common NTC or PTC thermistors, PT100 sensors provide much higher measurement precision and commonly use in industrial automation, laboratory equipment, medical devices, and scientific instrumentation. However, because RTDs have relatively low resistance values, they require specialized signal conditioning to achieve accurate readings.

The MAX31865 solves this challenge by precisely measuring the ratio between the RTD resistance and a reference resistor, then converting it into digital data using its high-resolution ADC. It supports 2-wire, 3-wire, and 4-wire RTD configurations, with automatic lead resistance compensation for 3-wire and 4-wire sensors to improve measurement accuracy.

In addition, the MAX 31865 features ±45V input overvoltage protection and integrated fault detection, including open-circuit, short-circuit, and cable fault monitoring. Most breakout modules include a 430Ω precision reference resistor for PT100 sensors, while replacing it with a 4300Ω resistor allows compatibility with PT1000 sensors. With its simple SPI interface and available Arduino libraries, the module makes professional-grade RTD temperature measurement easy to implement in embedded systems.

MAX 31865 Technical Specifications

The MAX 31865 Sensor Module is designed for accurate and reliable RTD temperature measurement. Below are its main technical specifications:

Key Features

High Precision Measurement

The integrated 15-bit Delta-Sigma ADC delivers precise resistance measurements with a nominal temperature resolution of 0.03125°C, enabling highly accurate temperature monitoring.

Supports PT100 and PT1000

The MAX 31865 supports platinum RTDs from 100Ω to 1kΩ at 0°C, including both PT100 and PT1000 sensors.

Compatible with Multiple Wiring Configurations

The module works with:

· 2-wire RTD

· 3-wire RTD

· 4-wire RTD

This flexibility allows users to choose the appropriate sensor based on cost and required accuracy.

SPI Communication Interface

The SPI-compatible interface enables fast communication with almost every popular microcontroller including Arduino, ESP32, STM32, Raspberry Pi, PIC, and AVR devices.

Built-in Fault Detection

Integrated diagnostics can detect:

· Open RTD

· Shorted RTD

· Short to supply

· Short to ground

· Overvoltage conditions

These features greatly increase system reliability.

Fully Differential Reference Inputs

Differential reference inputs improve measurement accuracy by minimizing electrical noise and common-mode interference.

Fast Conversion Speed

The module completes one temperature conversion in 21 ms (maximum), making it suitable for real-time monitoring applications.

Excellent Measurement Accuracy

The MAX 31865 maintains approximately ±0.5°C accuracy across its operating conditions when used with a quality RTD sensor.

MAX31865 Module Pinout

Table

How the MAX31865 Works

The MAX 31865 operates by passing a precisely controlled current through the RTD sensor and measuring the resulting voltage drop.

Using a precision reference resistor, the converter calculates the resistance ratio between the RTD and the reference resistor. A built-in 15-bit Delta-Sigma ADC digitizes this ratio, which is then transferred to the host microcontroller over SPI.

The microcontroller uses the measured resistance along with the Callendar–Van Dusen equation or library functions to calculate the actual temperature.

For 3-wire and 4-wire RTD configurations, the MAX 31865 automatically compensates for cable resistance, significantly improving measurement accuracy over long cable runs.

Arduino Wiring

Example SPI connections:

MAX31865 → Arduino Uno

· 3V3 → 3.3V

· GND → GND

· CLK → D13

· SDI → D11

· SDO → D12

· CS → D10

Connect the PT100 sensor to the FORCE+, FORCE−, RTDIN+, and RTDIN− terminals according to the sensor wiring type (2-wire, 3-wire, or 4-wire).

MAX31865 Sensor Module Application

The MAX 31865 widely use wherever require accurate and stable temperature measurement.

Industrial Automation

Used in process control systems, PLCs, industrial ovens, and manufacturing equipment.

Laboratory Equipment

Suitable for precision instruments, scientific research, and calibration systems requiring accurate temperature monitoring.

HVAC Systems

Monitors heating, ventilation, refrigeration, and air conditioning equipment.

Medical Equipment

Provides reliable temperature sensing for laboratory and healthcare devices.

Environmental Monitoring

Used in weather stations, climate monitoring systems, and environmental data loggers.

Food Processing

Measures temperature during food production, storage, and transportation.

Energy Systems

Monitors batteries, solar equipment, and power generation systems.

Educational Projects

Popular among students and hobbyists for learning SPI communication and RTD temperature sensing.

MAX31865 PDF Datasheet

The data sheet provides complete technical information, including electrical characteristics, timing diagrams, SPI communication protocol, application circuits, reference designs, and register descriptions. You can check for more detailed design information.

Frequently Asked Questions [FAQ]

What is the use of MAX31865?

The MAX 31865 is used to interface platinum RTD temperature sensors, such as PT100 and PT1000, with microcontrollers. It converts RTD resistance into digital temperature data, providing high accuracy, fault detection, and SPI communication for industrial, laboratory, HVAC, and embedded temperature measurement applications.

What is the price of MAX31865?

The MAX 31865 IC typically costs around US$4–12, while complete breakout modules usually range from US$9–20, depending on the manufacturer, board quality, included precision components, and supplier.

What is the temperature calculation for MAX31865?

The MAX 31865 measures RTD resistance and calculates temperature using the Callendar–Van Dusen equation or software libraries. Most Arduino libraries automatically convert the measured resistance into temperature, eliminating the need for manual calculations.

Is PT100 a thermistor or RTD?

PT100 is an RTD (Resistance Temperature Detector) rather than a thermistor. It uses platinum as its sensing element and has a resistance of 100Ω at 0°C. RTDs provide higher accuracy, better stability, and improved repeatability compared to most thermistors.

How to connect a PT100 temperature sensor?

Connect the PT100 sensor to the MAX 31865 according to its wiring type. Two-wire sensors connect directly, while three-wire and four-wire sensors use additional leads for cable resistance compensation, resulting in improved measurement accuracy.

Is PT100 2 wire or 3 wire?

PT100 sensors are available in 2-wire, 3-wire, and 4-wire versions. Two-wire models are economical, three-wire versions are the most common in industry due to lead resistance compensation, and four-wire sensors provide the highest measurement accuracy.

Conclusion

The MAX31865 PT100 Temperature Sensor Module is one of the best solutions for precision RTD temperature measurement. With support for PT100 and PT1000 sensors, compatibility with 2-wire, 3-wire, and 4-wire configurations, a high-resolution 15-bit ADC, integrated fault detection, and SPI communication, it offers professional-level performance in an easy-to-use module. Whether you are developing industrial automation equipment, laboratory instruments, HVAC systems, or Arduino-based projects, the MAX 31865 provides reliable, accurate, and stable temperature measurements with minimal hardware complexity.

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