16 Channel Thermocouple Multiplexer for Raspi

A auxiliary board capable of handling 16 thermocouples and passing their temperatures to a Raspberry Pi via SPI

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An SPI board which allows temperature measurement from 16 thermocouples to a Raspberry Pi. Temperature is measured using a Maxim 31856. It will handle different thermocouple types attached and a temperature range from -200 C to + 1700 C (Thermocouple Dependant) Example Python software allows the direct display to screen and periodic logging to file.

This project is released under the Creative Commons Attribution licence CC-BY. This license lets others distribute, remix, tweak, and build upon our work, even commercially, as long as they credit us for the original creation.

Measuring Temperature

Thermocouples are thin wires of two different types. The most common are Type T which can measure a range of temperature between -270 to 370C. The unit can handle other thermocouple types for different temperature ranges. Thermocouples are connected together at one end. This end is generally referred to as the Hot Junction. The other end connects to your measurement device and is known as the cold junction. A voltage proportional to the difference between the Cold Junction and the Hot Junction temperature is generated by this temperature gradient. This voltage can be corrected and read as a temperature.

This project allows up to 16 thermocouples to be connected and their temperature read in turn. The normalisation and compensation for the ambient temperature are automatically applied and the end temperatures displayed or logged to a comma separated list in a file. Temperatures are displayed and logged in Celsius. Conversions to Fahrenheit can be done by the end user if required.

PiPlay Temperature Circuit Board

The designed circuit board consists of two Analog Devices multiplexer chips for switching between the attached thermocouples and a Maxim Precision Thermocouple to Digital converter. It also has the termination screw terminals for the attachment of the thermocouples. The board also can detect an open circuit thermocouple and flag an error to the operator.

Raspberry Pi

The project is based on a Raspberry Pi which drives the Serial Peripheral Interface (SPI) to set the Thermocouple being read and to read the temperatures. Any device capable of SPI transactions could be used if the end user prefers


Software is written for the Raspberry Pi in Python which can read and display temperatures to the screen. It can also periodically log to a file in comma separated variable form. That file can then be imported to a spreadsheet and graphed if wanted.

Software is available for download in the Files area of this project. Software is in a Tarball format and a discussion on setting up your environment will be available in the Build Instructions area soon.

Screen Output

When running the screen is updated with the readings from all active thermocouples. The names provided for each channel in the .INI file will also be shown in brackets on the screen. This screen update occurs periodically as set in the variable display_interval in the .INI file.


In this example one of the thermocouples is showing a Fault condition.  Channel 1 with the name of Tc 1. This occurs if the thermocouple becomes open circuit or disconnected.

The outputted header shows the time and the number of seconds until the display will update and the number of seconds until the next time temperatures are logged to file. These times are set within the .INI file and a further discussion of that file is shown below.

Configuration (INI) file

Configuring the software to read Thermocouples is done in a text based configuration file. Any text editor is able to edit this file. There are a number of sections which are described below.


These are the global level configuration parameters.

# Aquisition and Logging intervals in seconds
display_interval = 300
logging_interval = 600

# Logging On/Off
logoutput = On

# Maximum Log file size in Megabytes When the maximum size is reached a new file will be created and the previous file renamed with a date/time suffix.
logfile_maximum = 1

Much of these settings are self evident. display_interval...

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Gerbers TC

Gerber files for PCB fabrication

Zip Archive - 90.17 kB - 08/23/2019 at 07:32



KiCad PCB file ver 1.3

kicad_pcb - 288.32 kB - 08/23/2019 at 07:30


x-kicad-schematic - 18.93 kB - 08/20/2019 at 07:30



Circuit Diagram Version 1.2 in PDF

Adobe Portable Document Format - 57.83 kB - 08/20/2019 at 07:29



Python Code to run board.

gzip - 12.52 kB - 05/04/2019 at 13:16


View all 7 files

  • 2 × U1,U2 ADG1607 Analogue Multiplexer
  • 1 × U3 MAX31856 Thermocouple A/D-SPI interface
  • 8 × C1,C2,C3,C4, C5,C6,C7,C8 100nF Ceramic 1206
  • 1 × C9 10uF Tantalum B Case
  • 2 × R1,R2 0 Ohm 1206

View all 7 components

  • Update PCB to Version 1.3 (part 2)

    piplay08/30/2019 at 07:23 0 comments

    The Ver.1.3 PCBs arrived today. I sent the Gerber files on Monday night and the PCBs were on my doorstep Friday afternoon. The price was AU$2.00 for the boards and AU$27.00 for DHL delivery. 

    I will attempt to get one assembled and tested over the week end.

    I just noticed looking at them that I have the +- symbols on the overlay around the wrong way..........Bugger!

  • Update PCB to Version 1.3

    piplay08/23/2019 at 07:41 0 comments

    Posted version 1.3 PCB file and compressed Gerber files. The PCB has been modified but is untested. It "Should" work but it will b e a couple of weeks before I get around to testing it. If you are not feeling brave, the version 1.2 PCB is still available. It works but has 2 unnecessary resistors that have been removed in 1.3. You can fit any value from 0 to a few hundred ohms and it will work.

  • Update Circuit diagram to Ver. 1.2

    piplay08/20/2019 at 07:43 0 comments

    Updated circuit diagram to Ver 1.2

    The circuit has been revised to reflect the removal of the two series resistors. This is as a result of the observation by Hwansoo Suh questioning the function of these components. They are there to protect the input of the converter chip from excess common mode voltage. As the multiplexer will be destroyed by anything much over +3/-0.6 volts the resistor seems a bit pointless. 

    The PCB is yet to be updated. At this stage if you use the Ver 1.1 PCB any value between 0 Ohm to 1K will work. I will publish an updated version as time permits.

  • Hardware Assembly Instructions

    piplay06/10/2019 at 11:52 0 comments

    Video of Maxim Thermocouple chip added.

  • Software Configuration Uploaded

    piplay05/02/2019 at 11:50 0 comments

    Software configuration instructions have been uploaded.

  • Minor Software Update

    piplay05/01/2019 at 08:18 0 comments

    A minor software update was uploaded to fix a problem with display when temperatures drop from 3 digit to two digit. Version number was not updated only date suffix.

  • Software Uploaded, INI file described.

    piplay04/28/2019 at 06:56 0 comments

    An upload of the Python code to log from the board and display to screen has been uploaded. Details on how to install it and the supporting libraries needed will be added to the Build Instructions soon

  • Update to Description & Component lists.

    piplay04/25/2019 at 06:12 0 comments

    Component lists and Circuit Diagrams uploaded. General project description added.

  • Project Start Info

    piplay04/22/2019 at 12:19 0 comments

    Project is fundamentally complete at a hardware level. Software is in progress but should be completed within a month. More details on assembly of the PCB will be posted soon.

View all 9 project logs

  • 1
    Hardware - Attaching the Maxim chip

    The video demonstrates the start of some experiments in improving the performance of the device by improving the thermal coupling of the MAX31856 to the PCB.This will be tested in comparison to an earlier board, eventually.

  • 2
    Software - Setup your Raspberry Pi to run the Thermocouple read program.

    Make sure the SPI subsystem is Enabled

    Run the Raspberry Pi configuration tool

    sudo raspi-config

    When this starts go to the Interfacing Options, then to SPI section. You will be prompted to enable or disable the interface.

  • 3
    Software - Install the needed package libraries.

    Using the Python Package Installer (pip) install the packages required for the project.

    sudo pip install psutil
    sudo pip install configparser
    sudo pip install spidev
    sudo pip install spi

View all 4 instructions

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