Pinouts

The MAX31865 is a tiny surface mount chip, and it needs a lot of other parts to make it work, so we've got it on a nice breakout board for you. You can control the chip and read data from it using the breakouts at the bottom. Let's go thru these!

Power Pins:

  • Vin - this is the power pin. Since the chip uses 3 VDC, we have included a voltage regulator on board that will take 3-5VDC and safely convert it down. To power the board, give it the same power as the logic level of your microcontroller - e.g. for a 5V micro like Arduino, use 5V
  • 3Vo - this is the 3.3V output from the voltage regulator, you can grab up to 100mA from this if you like
  • GND - common ground for power and logic

SPI Logic pins:

All pins going into the breakout have level shifting circuitry to make them 3-5V logic level safe. Use whatever logic level is on Vin!

  • SCK - This is the SPI Clock pin, its an input to the chip
  • SDO - this is the Serial Data Out / Master In Slave Out pin, for data sent from the MAX31865 to your processor
  • SDI - this is the Serial Data In / Master Out Slave In pin, for data sent from your processor to the MAX31865
  • CS - this is the Chip Select pin, drop it low to start an SPI transaction. Its an input to the chip

If you want to connect multiple MAX31865's to one microcontroller, have them share the SDI, SDO and SCK pins. Then assign each one a unique CS pin.

  • RDY (Ready) - is a data-ready indicator pin,  you can use this pin to speed up your reads if you are writing your own driver. Our Arduino driver doesn't use it to save a pin

Sensor Terminal Blocks

If you have an RTD sensor, you need to connect it somehow! the terminal block area is where you can clamp down to the sensor wires.

There are four contacts, but you can use 2, 3 or 4 wire sensors. You may need to solder or jumper some pads depending on how many wires you want to use. You can also use a 3 or 4 wire sensor as a 3-wire or 2-wire sensor (just don't connect the extra wires).

Check the RTD wiring page for details on how to connect the sensor you've got!

Configuration Jumpers

By default the sensor is wired up for 4-wire RTD usage but can be set up for 2 or 3 wire very easily.

For 4-wire usage, do nothing with the jumpers!

For 3-wire usage. Solder closed the jumper labeled 2/3 Wire and cut the wire connecting the left side of the 2-way jumper right above Rref. Then solder closed the right side labeled 3

For 2-wire usage, solder closed the two triangular jumpers below the terminal blocks (or put short wire jumpers between the two terminal blocks on either side (essentially jumpering the two right side terminal holes together, and same for left side)

Check the RTD wiring page for details on how to connect the sensor you've got!

This guide was first published on Nov 15, 2016. It was last updated on Nov 15, 2016. This page (Pinouts) was last updated on Nov 20, 2019.