Digital temperature sensors

Fig. 1: DS18B20 pinout.


The Dallas DS18B20 is a low cost temperature sensor with a digital interface.

It has three pins:

There must be a resistor (typically 4.7k) connected between the data line and the power line (Fig. 2). In electronics terminology, we say that the data line is “pulled up” by the resistor.


Fig. 2: Breadboard layout for temperature sensor circuit.

Fig. 2: Breadboard layout for temperature sensor circuit.


#include <OneWire.h>
#include <DallasTemperature.h>

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

// Set up the necessary objects to interface with the sensors
OneWire oneWire(2); // Data wire is connected to pin 2 on the Arduino
DallasTemperature sensors(&oneWire); // The data wire contains Dallas temperature sensors

// How many sensors to support?
#define MAX_SENSORS 5

// Create variables to hold the device addresses
int num_sensors;
DeviceAddress addresses [MAX_SENSORS];

 * Setup function. Here we do the basics
void setup(void)
  // put your setup code here, to run once:

  // Set the baud rate

  // Scan for temperature sensors
  num_sensors = sensors.getDeviceCount();

  // Print out how many sensors we found
  Serial.print("Found ");
  Serial.print(" device(s).");

  // Every DS18B20 sensor has a globally unique serial number,
  // called an address. We need the address to speak to a
  // particular sensor. Here we scan for the addresses of each
  // connected device. 
  for (int i = 0; i < num_sensors; i++) {
    // Read its address
    sensors.getAddress(addresses[i], i);

    // Instruct it to use 12 bit precision, which is the maximum.
    // Other choices are 9, 10, 11 and 12.
    sensors.setResolution(addresses[i], 12);

    // Print out a message
    Serial.print("Device ");
    Serial.print(" address is ");

void loop(void)
  // put your main code here, to run repeatedly:

  // Request temperature from all sensors
  sensors.requestTemperatures(); // Send the command to get temperatures

  // Read the temperature from every sensor
  for (int i = 0; i < num_sensors; i++) {
    float tempC = sensors.getTempC(addresses[i]);
    Serial.print("Sensor ");
    Serial.print(" temp: ");
    Serial.print(" C");


// Function to print a device address
void printAddress(DeviceAddress deviceAddress)
  for (int i = 0; i < 8; i++)
    if (deviceAddress[i] < 16) {
    Serial.print(deviceAddress[i], HEX);
    if (i < 7) {


Experiment with the above code.

Extension task

Sharing a sensor with the person next to you, connect two sensors (Fig. 3).

Fig. 3: Breadboard layout for two sensor circuit.

Fig. 3: Breadboard layout for two sensor circuit.

How similar are the temperature measurements of the two different sensors when they are adjacent?

Application ideas

These sensors can be daisy-chained to make a long string. You use a single pull-up resistor for the whole string (Fig. 4).

Fig. 4: Breadboard layout for temperature sensor circuit.

Fig. 4: Breadboard layout for temperature sensor circuit.

These can be used to examine microclimates, e.g. the temperature every 30 cm up the bank of a dry creek bed from shade to sun. You can also deploy the “sensor strings” in built environments, e.g. to look at the vertical temperature gradients in buildings.

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