Precision Temperature with the MAX31865 and a PT100

When you need temperature readings that are stable and repeatable over a wide range, a PT100 resistance probe is a classic choice, and the MAX31865 is the chip that makes it easy to read. Describe your measurement project to Compoden's AI build assistant and it returns a recommended parts list, wiring, code, and a shipped kit, so you can focus on the result rather than the conversion math.

What a PT100 is

A PT100 is a resistance temperature detector, or RTD, whose resistance changes in a well-defined way as temperature changes. The "100" refers to its nominal resistance at a reference temperature. Because that resistance-to-temperature relationship is well characterized and stable over time, PT100 probes are favored where repeatability matters more than low cost.

Why you need the MAX31865

Reading an RTD accurately means measuring small resistance changes without letting the measuring current heat the element. The MAX31865 is a dedicated RTD-to-digital converter that handles this for you. It drives the RTD, measures the resistance ratio against a known reference resistor, and outputs a digital value over SPI, removing the need to build a precise analog front end yourself.

Two-, three-, and four-wire probes

PT100 probes come in two-, three-, and four-wire forms, and the wiring scheme affects accuracy. Extra wires let the converter cancel out the resistance of the lead wires themselves, which matters when the probe sits far from the board. The MAX31865 supports these configurations, and you should match the board's wiring jumpers to the probe you actually have, with the reference resistor matched to the PT100 type.

Wiring and reading over SPI

The MAX31865 talks over SPI, so you connect clock, chip select, and the data lines plus power and ground. It works with Arduino, ESP32, and Raspberry Pi. The probe connects to the dedicated RTD terminals according to its wire count. Once wired, your code requests a reading and converts the resistance ratio into a temperature value using the standard RTD relationship.

Build it with Compoden's AI

Matching a PT100, the right wiring mode, and the correct reference resistor is the part that trips people up. Tell Compoden's AI build assistant something like "precise temperature logger with a PT100 probe," and it proposes the parts, wiring, and starter code, then ships the kit across India. Browse our full catalog for enclosures and displays to finish the build.

Need temperature you can trust? Describe your setup to Compoden's AI build assistant and get a PT100 kit ready to assemble.

FAQ

Why choose a PT100 over a cheaper sensor? Its resistance-to-temperature behavior is well defined and stable, which makes readings repeatable over time and across a wide range.

Does the wire count of the probe matter? Yes; three- and four-wire probes let the MAX31865 cancel lead resistance, improving accuracy when the probe is far from the board.

How does the MAX31865 connect to my board? It uses SPI and works with Arduino, ESP32, and Raspberry Pi after matching logic voltage.