Onboard MAX31865 Usage Instructions

Important Notice

• The standard thermistor interface of SHT36-V3 only supports PT1000.
• If your toolboard has the MAX31865 chip onboard, you can connect PT100 or PT1000 sensors with 2/3/4 wire configuration via the PH2.0 4P interface.

How to Determine if the Toolboard Supports MAX31865

Some SHT36 V3 kits support MAX31865. You can determine support by checking whether the MAX31865 chip is present on the toolboard (refer to the image below for physical location).

Configuration Method

Prerequisites for Configuration

• MAX31865 is typically used for high-precision temperature measurement on extruders or heated beds.
• The configuration examples below are based on modifications for an extruder.

1. Wiring and DIP Switch Settings

• Before using MAX31865, you must first set the 6-PIN DIP switch on the back of the toolboard (as shown in the image below), otherwise Klipper will not read the temperature correctly.

DIP Switch Settings Rules (switches are numbered 1 to 6 from left to right):

• Sensor Type Selection
  • For PT100: set switch 1 ON, switch 2 OFF.
  • For PT1000: set switch 1 OFF, switch 2 ON.
• Wire Configuration Selection
  • 2-Wire: switches 3, 5, 6 ON, switch 4 OFF.
  • 3-Wire: switches 4, 6 ON, switches 3, 5 OFF.
  • 4-Wire: switch 3 ON, switches 4, 5, 6 OFF.

Default State: All switches are down (OFF), MAX31865 functionality is disabled.

2. Modify Klipper Configuration File

Original Configuration Snippet (using standard thermistor):

[extruder]
# ... other configurations ...
sensor_type: ATC Semitec 104GT-2
sensor_pin: SHT36:gpio27
# ... other configurations ...

Modification Steps:

1. Comment out or delete the original sensor_type and sensor_pin lines.
2. Add the following MAX31865-specific configuration:

[extruder]
# ... other configurations ...
sensor_type: MAX31865
sensor_pin: SHT36:gpio17
spi_bus: spi0_gpio4_gpio3_gpio2
# Note: The following two parameters must be set correctly according to your sensor model!
rtd_reference_r: 430    # Set to 430 for PT100, 4300 for PT1000
rtd_nominal_r: 100      # Set to 100 for PT100, 1000 for PT1000
# ... other configurations ...

3. Important Notes

• Parameter Matching: The values of rtd_reference_r and rtd_nominal_r must match the sensor you are using (PT100 or PT1000), otherwise the temperature readings will be severely incorrect.
• Wiring Check: Ensure the sensor is correctly wired to the PH2.0 4P interface and matches the wire configuration set via the DIP switch.
• Exclusive Use: After enabling MAX31865, the standard thermistor interface on gpio27 will no longer be available.

Configure PT1000 Sensor on Standard Thermistor Port

• Important Prerequisite: Before connecting a PT1000 sensor to the standard thermistor port, ensure the corresponding jumper on the toolboard is properly connected.

Original Configuration

Original Configuration Snippet (using standard NTC thermistor):

[extruder]
# ... other configurations ...
sensor_type: ATC Semitec 104GT-2
sensor_pin: SHT36:gpio27
# ... other configurations ...

Modified Configuration

Modification Steps:

1. Change the value of sensor_type to PT1000.
2. Add the pullup_resistor parameter and set it to 1000.

Modified Configuration:

[extruder]
# ... other configurations ...
sensor_type: PT1000
sensor_pin: SHT36:gpio27
pullup_resistor: 1000
# ... other configurations ...

Notes

• This configuration is applicable only for the standard thermistor port (GPIO27) of SHT36-V3.
• The pullup_resistor: 1000 parameter must be configured.