Adafruit MAX31856 Universal
Thermocouple Amplifier
Created by lady ada
https://learn.adafruit.com/adafruit-max31856-thermocouple-amplifier
Last updated on 2021-11-15 06:47:36 PM EST
©Adafruit Industries
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Table of Contents
Overview
3
Pinouts
5
• Power Pins:
• SPI Logic pins:
• Additional Pins
5
6
6
Assembly
7
• Prepare the header strip:
• Add the breakout board:
• And Solder!
7
7
8
Wiring & Test
•
•
•
•
•
SPI Wiring
Download Adafruit_MAX31856 library
Attach Thermocouple
Load Demo
Library Reference
10
11
11
12
13
15
Python & CircuitPython
17
•
•
•
•
•
•
18
18
19
19
20
20
CircuitPython Microcontroller Wiring
Python Computer Wiring
CircuitPython Installation of MAX31856 Library
Python Installation of MAX31856 Library
CircuitPython & Python Usage
Full Example Code
Python Docs
21
Downloads
21
• Files
• Schematic
• Fabrication Print
21
21
22
©Adafruit Industries
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Overview
Thermocouples are very sensitive, requiring a good amplifier with a coldcompensation reference, as well as calculations to handle any non-linearities. For a
long time we've suggested our MAX31855K breakout, which works great but is only
for K-type thermocouples. Now we're happy to offer a great new thermocouple
amplifier/converter that can handle just about any type of thermocouple, and even
has the ability to give you notification when the temperature goes out of range, or a
fault occurs. Very fancy!
This converter communicates over 4-wire SPI and can interface with any K, J, N, R, S,
T, E, or B type thermocouple
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This breakout does everything for you, and can be easily interfaced with any
microcontroller, even one without an analog input. This breakout board has the chip
itself, a 3.3V regulator and level shifting circuitry, all assembled and tested. Comes
with a 2 pin terminal block (for connecting to the thermocouple) and pin header (to
plug into any breadboard or perfboard). We even added inline resistors and a filter
capacitor onboard for better stability, as recommended by Maxim. Goes great with our
1m K-type thermocouple (http://adafru.it/270) or any other thermocouple, really!
• Works with any K, J, N, R, S, T, E, or B type thermocouple
• -210°C to +1800°C output in 0.0078125° resolution - note that many
thermocouples have about ±2°C to ±6°C accuracy or worse depending on the
temperature and type, so the resolution will be a lot better than the accuracy!
• Internal temperature reading
• 3.3 to 5v power supply and logic level compliant!
• SPI data requires any 4 digital I/O pins.
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Pinouts
Power Pins:
• Vin - this is the power pin. Since the sensor 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
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• 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 / Microcontroller In Sensor Out pin, for data
sent from the MAX31856 to your processor
• SDI - this is the Serial Data In / Microcontroller Out Sensor In pin, for data sent
from your processor to the MAX31856
• 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 MAX31856's to one microcontroller, have them share
the SDI, SDO and SCK pins. Then assign each one a unique CS pin.
Additional Pins
There's two more pins that are available for advanced usage
• FLT - This is the Fault output. If you use the threshhold-notification capabilities of
the MAX31856 you can monitor this pin, when it goes low there's a fault!
• DRDY - This pin is used for advanced uses where you tell the sensor to begin a
reading and then wait for this pin to go low. We don't use it in our library code
because we keep it simple with a delay/wait, but it is available in case you need
it!
©Adafruit Industries
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Assembly
Prepare the header strip:
Cut the strip to length if necessary. It will
be easier to solder if you insert it into a
breadboard - long pins down.
Add the breakout board:
Place the breakout board over the pins
so that the short pins poke through the
breakout pads
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And Solder!
Be sure to solder all 5 pins for reliable
electrical contact.
(For tips on soldering, be sure to check
out ourGuide to Excellent
Soldering (https://adafru.it/aTk))
Now you can do the terminal block, this
is what you'll use to attach the
thermocouple since you cannot solder to
thermocouples
The terminal block goes on the top with
the open ends pointing out
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Solder the two pads as you did with the
plain header. They're quite large and
require a lot of solder
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Insert the thermocouple wires and
tighten down the clamps with a small
Phillips or flat screwdriver
That's it! you are now ready to wire and
test
Wiring & Test
You can easily wire this breakout to any microcontroller, we'll be using an Arduino. For
another kind of microcontroller, as long as you have 4 available pins it is possible to
'bit-bang SPI' or you can use hardware SPI if you like. Just check out the library, then
port the code.
©Adafruit Industries
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Fritzing diagram.fzz
https://adafru.it/rAK
SPI Wiring
Since this is a SPI-capable sensor, we can use hardware or 'software' SPI. To make
wiring identical on all Arduinos, we'll begin with 'software' SPI. The following pins
should be used:
• Connect Vin to the power supply, 3V or 5V is fine. Use the same voltage that the
microcontroller logic is based off of. For most Arduinos, that is 5V
• Connect GND to common power/data ground
• Connect the SCK pin to Digital #13 but any pin can be used later
• Connect the SDO pin to Digital #12 but any pin can be used later
• Connect the SDI pin to Digital #11 but any pin can be used later
• Connect the CS pin Digital #10 but any pin can be used later
Later on, once we get it working, we can adjust the library to use hardware SPI if you
desire, or change the pins to other
Download Adafruit_MAX31856 library
To begin reading sensor data, you will need to install Adafruit MAX31856 from the
Arduino library manager.
©Adafruit Industries
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Open up the Arduino library manager:
Search for the Adafruit MAX31856 library and install it
We also have a great tutorial on Arduino library installation at:
http://learn.adafruit.com/adafruit-all-about-arduino-libraries-install-use
Attach Thermocouple
You'll need to attach a thermocouple, for this demo we'll be using a K-type but you
can adjust the demo if you do not have a K-type handy!
©Adafruit Industries
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Load Demo
Open up File->Examples->Adafruit_MAX31856->max31856 and upload to your
Arduino wired up to the sensor. Adjust the max.setThermocoupleType(MAX31856_T
CTYPE_K) line if necessary.
Upload to your Arduino and open up the serial console at 115200 baud to see a print
out of the cold junction temperature (temperature of the microcontroller chip) and the
thermocouple temperature (temperature detected at the end of the thermocouple
probe
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You can also see some of the faults that are detectable by say disconnecting one of
the pins:
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Library Reference
You can start out by creating a MAX31856 object with either software SPI (where all
four pins can be any I/O) using
// Use software SPI: CS, DI, DO, CLK
Adafruit_MAX31856 max = Adafruit_MAX31856(10, 11, 12, 13);
Or you can use hardware SPI. With hardware SPI you must use the hardware SPI pins
for your Arduino - and each arduino type has different pins! Check the SPI reference
to see what pins to use. (https://adafru.it/d5h)
In this case, you can use any CS pin, but the other three pins are fixed
// use hardware SPI, just pass in the CS pin
Adafruit_MAX31856 max = Adafruit_MAX31856(10);
Once started, you can initialize the sensor with
max.begin()
You'll also need to set the thermocouple type, remember there's a lot of options! Set
the type with:
max.setThermocoupleType(MAX31856_TCTYPE_xxx)
Your options for the TCTYPE are:
•
•
•
•
•
•
•
•
•
•
MAX31856_TCTYPE_B
MAX31856_TCTYPE_E
MAX31856_TCTYPE_J
MAX31856_TCTYPE_K
MAX31856_TCTYPE_N
MAX31856_TCTYPE_R
MAX31856_TCTYPE_S
MAX31856_TCTYPE_T
MAX31856_VMODE_G8
MAX31856_VMODE_G32
The last two are not thermocouple types, they're just 'plain' voltage readings (check
the datasheet for more details, we don't use these modes in the library)
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If you're ever not sure which mode you're in, query it with
max.getThermocoupleType()
Once that's set you can read the cold junction temperature, which will return a
floating point Celsius reading. This is the temperature detected inside the MAX31856
chip ('ambient' temp)
max.readCJTemperature()
Or, of course, the temperature at the end/tip of the thermocouple, likewise a floating
point #
max.readThermocoupleTemperature()
Faults
The MAX31856 has a wide-ranging fault mechanism that can alert you via pin or
function when something is amiss. Don't forget to test this functionality before relying
on it!
You can read faults with
max.readFault()
Which will return a uint8_t type with bits set for each of 8 different fault types. You
can test for each one with this set of code:
uint8_t fault = max.readFault();
if (fault) {
if (fault & MAX31856_FAULT_CJRANGE)
Fault");
if (fault & MAX31856_FAULT_TCRANGE)
Fault");
if (fault & MAX31856_FAULT_CJHIGH)
Fault");
if (fault & MAX31856_FAULT_CJLOW)
Fault");
if (fault & MAX31856_FAULT_TCHIGH)
Fault");
if (fault & MAX31856_FAULT_TCLOW)
Fault");
if (fault & MAX31856_FAULT_OVUV)
Fault");
if (fault & MAX31856_FAULT_OPEN)
Fault");
}
©Adafruit Industries
Serial.println("Cold Junction Range
Serial.println("Thermocouple Range
Serial.println("Cold Junction High
Serial.println("Cold Junction Low
Serial.println("Thermocouple High
Serial.println("Thermocouple Low
Serial.println("Over/Under Voltage
Serial.println("Thermocouple Open
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The last two faults are built in. For the low/high threshholds, you can set those with
two functions.
For the cold junction (chip) temp, use:
max.setColdJunctionFaultThreshholds(lowtemp, hightemp)
Where lowtemp and hightemp range between -127 and +127 Centigrade (the chip
wont function down to -127 but that's the lowest number you can put in.
For the thermocouple, use
setTempFaultThreshholds(lowtemp, hightemp)
Where lowtemp and hightemp are floating point numbers with a range of -4096 to
+4096 and a resolution of 0.0625 degrees Centigrade
Python & CircuitPython
It's easy to use the MAX31856 sensor with Python and CircuitPython, and the Adafruit
CircuitPython MAX31856 (https://adafru.it/Gao) module. This module allows you to
easily write Python code that reads the temperature from the thermocouple.
You can use this sensor with any CircuitPython microcontroller board or with a
computer that has GPIO and Python thanks to Adafruit_Blinka, our CircuitPython-forPython compatibility library (https://adafru.it/BSN).
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CircuitPython Microcontroller Wiring
First, wire up a MAX31856 to your board exactly as shown on the previous pages for
Arduino. Here's an example of wiring a Feather M0 to the sensor:
• Board 3V to sensor VIN
• Board GND to sensor GND
• Board SCK to sensor SCK
• Board MISO to sensor SDO
• Board MOSI to sensor SDI
• Board D5 to sensor CS (or any
other free digital I/O pin)
Once wired to the microcontroller, make sure you connect a thermocouple to the
terminal on the breakout board.
Python Computer Wiring
Since there's dozens of Linux computers/boards you can use, this shows wiring for
Raspberry Pi. For other platforms, please visit the guide for CircuitPython on Linux to
see whether your platform is supported (https://adafru.it/BSN).
Here's the Raspberry Pi wired with SPI:
• Pi 3V to sensor VIN
• Pi GND to sensor GND
• Pi SCK to sensor SCK
• Pi MISO to sensor SDO
• Pi MOSI to sensor SDI
• Pi D5 to sensor CS (or any other
free digital I/O pin)
Once wired to the Raspberry Pi, make sure you connect a thermocouple to the
terminal on the breakout board.
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CircuitPython Installation of MAX31856 Library
Next, you'll need to install the Adafruit CircuitPython MAX31856 (https://adafru.it/Gao)
library on your CircuitPython board
First, make sure you are running the latest version of Adafruit CircuitPython (https://
adafru.it/tBa) for your board.
Next you'll need to install the necessary libraries to use the hardware. Carefully follow
the steps to find and install these libraries from Adafruit's CircuitPython library bundle
(https://adafru.it/ENC). For example the Circuit Playground Express guide has a great
page on how to install the library bundle (https://adafru.it/Bf2) for both Express and
non-Express boards.
Remember for non-Express boards like the Trinket M0, Gemma M0, and Feather/
Metro M0 basic you'll need to manually install the necessary libraries from the bundle:
• adafruit_max31856.mpy
• adafruit_bus_device
Before continuing, make sure your board's lib folder has the adafruit_max31856.mpy,
and adafruit_bus_device files and folders copied over.
Next connect to the board's serial REPL (https://adafru.it/Awz) so you are at the
CircuitPython >>> prompt.
Python Installation of MAX31856 Library
You'll need to install the Adafruit_Blinka library that provides the CircuitPython
support in Python. This may also require enabling I2C on your platform and verifying
you are running Python 3. Since each platform is a little different, and Linux changes
often, please visit the CircuitPython on Linux guide to get your computer ready (https
://adafru.it/BSN)!
Once that's done, from your command line run the following command:
• sudo pip3 install adafruit-circuitpython-max31856
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If your default Python is version 3 you may need to run 'pip' instead. Just make sure
you aren't trying to use CircuitPython on Python 2.x, it isn't supported!
CircuitPython & Python Usage
To demonstrate the usage of the sensor, initialize it and read the temperature.
Remember to attach a thermocouple to the terminal on the breakout!
First initialize the SPI connection and library by running:
import board
import digitalio
import adafruit_max31856
spi = board.SPI()
cs = digitalio.DigitalInOut(board.D5)
cs.direction = digitalio.Direction.OUTPUT
thermocouple = adafruit_max31856.MAX31856(spi,cs)
Now you can read the temperature property to retrieve the temperature from the
sensor in degrees Celsius:
print(thermocouple.temperature)
That's all there is to reading temperature with the MAX31856 and CircuitPython code!
Full Example Code
# SPDX-FileCopyrightText: 2021 ladyada for Adafruit Industries
# SPDX-License-Identifier: MIT
import board
import digitalio
import adafruit_max31856
# Create sensor object, communicating over the board's default SPI bus
spi = board.SPI()
# allocate a CS pin and set the direction
cs = digitalio.DigitalInOut(board.D5)
cs.direction = digitalio.Direction.OUTPUT
# create a thermocouple object with the above
thermocouple = adafruit_max31856.MAX31856(spi, cs)
# print the temperature!
print(thermocouple.temperature)
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Python Docs
Python Docs (https://adafru.it/G7C)
Downloads
Files
• Fritzing object in Adafruit Fritzing library (https://adafru.it/c7M)
• EagleCAD PCB files on GitHub (https://adafru.it/rAN)
• Library on GitHub (https://adafru.it/rAL)
• MAX31856 Datasheet (https://adafru.it/rAO)
Schematic
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Fabrication Print
©Adafruit Industries
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