PT100 RTD Temperature Sensor Amplifier - MAX31865

SPI amplifier breakout for PT100 or PT1000 platinum RTD probes, using the MAX31865 with onboard bias resistor and fault detection. Pair with a PT100 or PT1000 probe for precision laboratory-grade temperature measurement.

Logical pinout · physical placement not verified

VIN
Power input. Adafruit Learn states the onboard regulator takes 3-5VDC and should match the microcontroller logic level.
Type · PowerVoltage · 3-5VDC input
3Vo
3.3V regulator output. Adafruit Learn states up to 100mA is available.
Type · PowerVoltage · 3.3V output, up to 100mA
GND
Common ground for power and logic.
Type · GroundVoltage · 0V reference
SCK
SPI clock input to the MAX31865 breakout. Adafruit Learn states logic pins are level shifted and 3-5V logic safe at VIN logic level.
Type · SPIVoltage · 3-5V logic, follows VIN
SDOMISO
SPI serial data out from the MAX31865 to the processor.
Type · SPI, SignalVoltage · 3-5V logic, follows VIN
SDIMOSI
SPI serial data in from the processor to the MAX31865.
Type · SPI, SignalVoltage · 3-5V logic, follows VIN
CS
SPI chip-select input, driven low to start a transaction.
Type · SPIVoltage · 3-5V logic, follows VIN
RDY
Ready/data-ready indicator pin. Adafruit notes their Arduino driver does not use it.
Type · SignalVoltage · 3-5V logic, follows VIN
RTD terminal block contacts
Four terminal-block contacts for 2-wire, 3-wire, or 4-wire RTD sensor wiring. Adafruit Learn notes jumper configuration changes for 2-wire and 3-wire use.
Type · Signal

Pin	Type	Function	Voltage
VIN	Power	Power input. Adafruit Learn states the onboard regulator takes 3-5VDC and should match the microcontroller logic level.	3-5VDC input
3Vo	Power	3.3V regulator output. Adafruit Learn states up to 100mA is available.	3.3V output, up to 100mA
GND	Ground	Common ground for power and logic.	0V reference
SCK	SPI	SPI clock input to the MAX31865 breakout. Adafruit Learn states logic pins are level shifted and 3-5V logic safe at VIN logic level.	3-5V logic, follows VIN
SDOMISO	SPI, Signal	SPI serial data out from the MAX31865 to the processor.	3-5V logic, follows VIN
SDIMOSI	SPI, Signal	SPI serial data in from the processor to the MAX31865.	3-5V logic, follows VIN
CS	SPI	SPI chip-select input, driven low to start a transaction.	3-5V logic, follows VIN
RDY	Signal	Ready/data-ready indicator pin. Adafruit notes their Arduino driver does not use it.	3-5V logic, follows VIN
RTD terminal block contacts	Signal	Four terminal-block contacts for 2-wire, 3-wire, or 4-wire RTD sensor wiring. Adafruit Learn notes jumper configuration changes for 2-wire and 3-wire use.

Logical pinout · physical placement not verified

Pin details

9 connections

VIN
Power input. Adafruit Learn states the onboard regulator takes 3-5VDC and should match the microcontroller logic level.
PowerVoltage · 3-5VDC input
3Vo
3.3V regulator output. Adafruit Learn states up to 100mA is available.
PowerVoltage · 3.3V output, up to 100mA
GND
Common ground for power and logic.
GroundVoltage · 0V reference
SCK
SPI clock input to the MAX31865 breakout. Adafruit Learn states logic pins are level shifted and 3-5V logic safe at VIN logic level.
SPIVoltage · 3-5V logic, follows VIN
SDOMISO
SPI serial data out from the MAX31865 to the processor.
SPI, SignalVoltage · 3-5V logic, follows VIN
SDIMOSI
SPI serial data in from the processor to the MAX31865.
SPI, SignalVoltage · 3-5V logic, follows VIN
CS
SPI chip-select input, driven low to start a transaction.
SPIVoltage · 3-5V logic, follows VIN
RDY
Ready/data-ready indicator pin. Adafruit notes their Arduino driver does not use it.
SignalVoltage · 3-5V logic, follows VIN
RTD terminal block contacts
Four terminal-block contacts for 2-wire, 3-wire, or 4-wire RTD sensor wiring. Adafruit Learn notes jumper configuration changes for 2-wire and 3-wire use.
Signal

Start wiring

I2C · SPI · Single data line · 3.3 – 5 V · Breakout

Verify supply voltage and logic levels before powering up.

Module pins: VIN, 3Vo, GND, SCK, SDO / MISO, SDI / MOSI, CS, RDY. Schematik maps them to your board in the app.

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