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MAX31855 / MAX6675 Thermocouple Amplifier~

This feature is not included in precompiled binaries

When compiling your build add the following to user_config_override.h:

#ifndef USE_MAX31855
#define USE_MAX31855  // Add support for MAX31855/MAX6675 K-Type thermocouple sensor using softSPI
#endif

This driver is used to read type-K thermocouples using a MAX31855 amplifier.

Configuration~

Tasmota Settings~

Parameter Connector Description
MX31855 CS # CS Chip select, wire a separate pin to each peripheral if using multiple.
MX31855 CLK CLK Along with power and DO, shared among peripherals.
MX31855 DO DO
Vin 3-5V if using Adafruit's breakout.
GND

Example Project~

This example shows two thermocouple amplifier breakouts wired up to one Huzzah ESP8266. The peripherals use the same CLK and DO pins, but each has a separate CS.

Tasmota Configuration~

This Tasmota configuration shows the thermocouples as well as unrelated I2C setup on GPIO4 and GPIO5.

screenshot of Tasmota configuration screenshot of Tasmota sensor view

Sensor data is reported like this:

tele/tasmota_30EF0B/SENSOR = {
  "Time":"2023-12-11T00:54:59",
  "MAX31855-0":{
    "Temperature":22.8,
    "ReferenceTemperature":23.6,
    "Error":0
  },
  "MAX31855-1":{
    "Temperature":22.5,
    "ReferenceTemperature":22.9,
    "Error":0
  },
  "TempUnit":"C"
}

The ReferenceTemperature, also known as "cold junction temperature", is the PCB temperature which is used as the basis for the thermocouple's voltage offset to find the thermocouple or "hot junection" temperature.

Home Assistant View~

The sensor values are autodiscovered in Home Assistant. In the screenshot below they have been renamed.

home assistant card screenshot

Wiring~

wiring on permaproto board