Measure temperature precisely with the DS18B20

The DS18B20 is a digital temperature sensor that talks over a single data wire, called the 1-Wire bus. It's accurate to about ±0.5 °C, much better than simple analog sensors, so it's great for aquariums, fridges and weather stations.

What you'll learn

• How the 1-Wire bus works
• How to use two libraries together
• How to print temperatures with decimals

What you need

• UNO R3 board (or any Arduino-compatible board) and USB cable
• DS18B20 temperature sensor module from the 45-in-1 kit
• 3 jumper wires

Step 1: Install the libraries

In Tools → Manage Libraries, install OneWire (by Paul Stoffregen) and DallasTemperature (by Miles Burton).

Step 2: Wiring

The 1-Wire bus needs a pull-up resistor (usually 4.7 kΩ) on the data line. The module has one on board, so you don't need to add it.

Step 3: The sketch

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

const int ONE_WIRE_PIN = 2;

OneWire oneWire(ONE_WIRE_PIN);
DallasTemperature sensors(&oneWire);

void setup() {
  Serial.begin(9600);
  sensors.begin();
  Serial.print("Sensors found: ");
  Serial.println(sensors.getDeviceCount());
}

void loop() {
  sensors.requestTemperatures();            // start a measurement
  float celsius = sensors.getTempCByIndex(0); // first sensor on the bus

  if (celsius == DEVICE_DISCONNECTED_C) {
    Serial.println("Sensor not found, check the wiring");
  } else {
    Serial.print("Temperature: ");
    Serial.print(celsius, 2); // 2 decimals
    Serial.println(" °C");
  }
  delay(1000);
}

How it works

Every DS18B20 has a unique 64-bit address, so many sensors can share one data wire. requestTemperatures() tells all sensors to measure, and getTempCByIndex(0) reads the first one found. A measurement at full resolution takes up to 750 ms, so one reading per second is a good rhythm.

Try this next

• Hold the sensor between your fingers and watch it climb towards body temperature.
• Compare it with the analog temperature sensor from the kit. Which one reacts faster, and which is steadier?

Troubleshooting

• "Sensors found: 0": check the wiring, especially that S is on pin 2.
• The reading is always -127 °C: that's the "disconnected" value. Check the power and ground pins.
• The reading is always 85 °C: that's the sensor's power-on value. Make sure requestTemperatures() is called before reading.