Wiring and Test

In this step we'll wire up the assembled breakout board to an Arduino. Any 1-Wire capable microcontroller can be used but we have example code for Arduino only.

You can wire up 1-Wire devices in two modes parasitic powered and externally powered
  • Parasitic power lets you have all data and power on a single data line + ground wire. Its more minimal but we believe it is a little more sensitive to power fluctuations
  • Externally powered has data on the single data line + ground wire, and then a separate power supply. It requires more wires but we think it is more stable in readings.
BOTH require level shifting on the data line if you are connecting up to a 5V microcontroller like an Arduino. If you are using a 3V logic microcontroller, you can skip the 4-channel level shifter we have in these images

We show 2 sensor boards in these photos, but you can connect as many as you like, 1-Wire supports any number of shared devices on a single data line.

External power

In this wiring style, each board is powered externally. Connect:

  1. GND to the Arduino Ground pin (black wires)
  2. Vin to the Arduino 5V pin (can also connect to an external battery of 3-5VDC) (red wires)
  3. Data shared connection to A1 on the level converter (green wire)
  4. A single 4.7K resistor connects from the shared data line to 3V
  5. B1 of the level converter connects to Arduino #2 (blue wire)
  6. Level shifter HV connects to Arduino 5V (red wire)
  7. Level shifter LV connects to Arduino 3V (yellow wire)
Click to see a bigger wiring photo

Parasitic Power


Alternatively you can use parasitic power to connect up MAX31850's - to do that basically follow the above except do not connect the VIN wires on the breakout boards

  1. GND to the Arduino Ground pin (black wires)
  2. Vin does not get connected
  3. Data shared connection to A1 on the level converter (green wire)
  4. A single 4.7K resistor connects from the shared data line to 3V
  5. B1 of the level converter connects to Arduino #2 (blue wire)
  6. Level shifter HV connects to Arduino 5V (red wire)
  7. Level shifter LV connects to Arduino 3V (yellow wire)

If you have the sensor far from the Arduino, you can extend the Data and GND lines going to each sensor by up to 10 meters!

Click to see a bigger wiring photo

Download Arduino libraries


For 1-Wire devices, we'll be using the OneWire library and a modified version of the DallasTemp library (Dallas was the name of the original company making 1-Wire devices, Maxim bought them later)

The original version of the DallasTemp library doesn't have support for the MAX31850, so we had to modify it! If you're having difficulty sensing the breakout sensors make sure you have completely removed any old copies of the libraries from your libraries and replaced them with ours

Start by downloading both OneWire and DallasTemp libraries from the GitHub repositories, or better yet, just click these buttons here:

Rename the uncompressed folder OneWire. Check that the OneWire folder contains OneWire.cpp and OneWire.h and an examples folder

Place the OneWire library folder your sketchbookfolder/libraries/ folder. You may need to create the libraries subfolder if its your first library. Restart the IDE. You can figure out your sketchbookfolder by opening up the Preferences tab in the Arduino IDE.

If you're not familiar with installing Arduino libraries, please visit our tutorial: All About Arduino Libraries!
Rename the uncompressed folder DallasTemp. Check that the DallasTemp folder contains DallasTemperature.cpp and DallasTemperature.h and an examples folder (you can ignore other files in the archive).

Place the DallasTemp library folder in your sketchbookfolder/libraries/ folder like you did with OneWire - and restart the IDE

Now you are ready to run the DallasTemp multiple example from the File->Examples->DallasTemp->multiple menu. Upload this sketch to your Arduino
OK now open up the serial console

First up, you should see how many sensors were detected. In our case its 2
Also whether parasite power is being used or not, its on the third line
You'll also see the device addresses, these are the unique 64-bit addresses for each sensor. You have a promise from Maxim that they will never recycle these numbers! All MAX31850 sensors start with 3B which is the family address. You can see the temperature printed out afterwards
Note that this address is not connected to the ADDR pins on the breakout! those are different address pins. You cannot change the 64-bit address, its permanently burned into the chip!

External vs Parasite power


Here is the same setup under external power. The temperature is much closer to the true temp (room temp, about 72 degrees F) because the power supply is more stable. If you are using parasite power you may need to calculate the temperature offset (calibrating the sensor) to get the true sensor at the location.

Writing your own sketch


OneWire and DallasTemp are very powerful but for most people, they just want to get temperatures printed out in their project!
Here is some super-basic code based on the Simple example to handle any number of sensors, simply printing out the temperature and the last two bytes of the unique ID number. You can see we figure out how many sensors are attached with
sensors.getDeviceCount()
which will let us know the # of connected sensors, and then can get the temperature from each one starting from index #0 up with
sensors.getTempCByIndex(index #)
The index #'s will always be sorted by address number so every time you start, the index #0 sensor will be the same as last time you started up. If you swap the sensors with another breakout, the index # may change so that's when you would have to check the code to figure out whether the index #'s are different
Download: file
#include <OneWire.h>
#include <DallasTemperature.h>

// Data wire is plugged into port 2 on the Arduino
#define ONE_WIRE_BUS 2

// Setup a oneWire instance to communicate with any OneWire devices (not just Maxim/Dallas temperature ICs)
OneWire oneWire(ONE_WIRE_BUS);

// Pass our oneWire reference to Dallas Temperature. 
DallasTemperature sensors(&oneWire);
DeviceAddress addr;

void setup(void)
{
  // start serial port
  Serial.begin(9600);
  Serial.println("Dallas Temperature IC Control Library Demo");

  // Start up the library
  sensors.begin();
}

void loop(void)
{ 
  // call sensors.requestTemperatures() to issue a global temperature 
  // request to all devices on the bus
  Serial.print("Requesting temperatures...");
  sensors.requestTemperatures(); // Send the command to get temperatures
  Serial.println("DONE");
  
  for (uint8_t s=0; s < sensors.getDeviceCount(); s++) {
    // get the unique address 
    sensors.getAddress(addr, s);
    // just look at bottom two bytes, which is pretty likely to be unique
    int smalladdr = (addr[6] << 8) | addr[7];
    
    Serial.print("Temperature for the device #"); Serial.print(s); 
    Serial.print(" with ID #"); Serial.print(smalladdr);
    Serial.print(" is: ");
    Serial.println(sensors.getTempCByIndex(s));  
  }
}

The Address pinouts


So if you're wondering how you can read those address pins, you can do so but the DallasTemp library doesn't support it, instead, you'll have to go with the lower-level OneWire library.

Open up the OneWire->MAX31850_Temperature example and load it into your Arduino.
Please Note - this example uses pin 10 instead of pin 2, for consistancy with the other OneWire examples. Either change OneWire ds(10); to OneWire ds(2); or switch your wiring
On the back of your MAX31850 breakout, cut the pads between the jumpers
. You can solder the jumpers on the back but we'll be showing wiring with colored wires. In this case, we connect A2 to 3V and the rest to ground, That will make a binary address of 0100 = 0x4
Now if you open up the serial console you should see the OneWire example code print out the data, address and temperature of the sensor. If you mess with the Ax wires you'll see this address value change from 0x00 to 0x0F. This can be a good way to deal with 'hot-swapping' in sensors with unique ROM addresses

More about OneWire and DallasTemp


Arduino Playground has some good resources on OneWire at http://playground.arduino.cc/Learning/OneWire and PJRC has documented it as well over at http://www.pjrc.com/teensy/td_libs_OneWire.html

This guide was first published on Feb 26, 2014. It was last updated on Feb 26, 2014.
This page (Wiring and Test) was last updated on Aug 10, 2020.