DS18B20 Temperature Sensor

The DS18B20 is a digital temperature sensor from Maxim Integrated that communicates over the 1-Wire protocol. It offers +/-0.5C accuracy, a wide temperature range, and the unique ability to operate multiple sensors on a single data pin — each sensor has a unique 64-bit ROM address for identification on the bus.

For this interfacing you need the following components:

• Arduino board (Uno, Nano, Mega, etc.)
• DS18B20 temperature sensor (TO-92 package or waterproof probe)
• 4.7k ohm resistor (1-Wire pull-up)
• Breadboard and jumper wires
• USB cable to connect Arduino to your computer

Schematic

Connect the DS18B20 to the Arduino as follows:

DS18B20 (TO-92)       Arduino
--------------        -------
VCC (pin 1 - left)   5V
DATA (pin 2 - center) Digital Pin 2
GND (pin 3 - right)  GND

A 4.7k ohm pull-up resistor must be connected between the DATA pin and VCC (5V). For the waterproof probe version (red, yellow, black wires), red = VCC, yellow = DATA, black = GND.

Pin Map

TO-92 Package (flat face toward you, pins down)

Waterproof Probe

Install necessary Library

Install the following libraries via the Library Manager (Tools > Manage Libraries):

1. OneWire by Jim Studt (or Paul Stoffregen)
2. DallasTemperature by Miles Burton

Alternatively, using arduino-cli:

arduino-cli lib install "OneWire"
arduino-cli lib install "DallasTemperature"

Code with complete explanation

This sketch reads temperature from a single DS18B20 sensor and prints the values to the Serial Monitor. It also demonstrates how to request temperatures from multiple sensors on the same bus.

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

#define ONE_WIRE_BUS 2

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

void setup()
{
  Serial.begin(9600);
  Serial.println("DS18B20 Temperature Sensor Test");

  sensors.begin();

  int deviceCount = sensors.getDeviceCount();
  Serial.print("Found ");
  Serial.print(deviceCount);
  Serial.println(" DS18B20 sensor(s)");
}

void loop()
{
  sensors.requestTemperatures();

  float tempC = sensors.getTempCByIndex(0);

  if (tempC == DEVICE_DISCONNECTED_C)
  {
    Serial.println("Error: Could not read temperature data");
  }
  else
  {
    float tempF = sensors.getTempFByIndex(0);

    Serial.print("Temperature: ");
    Serial.print(tempC);
    Serial.print(" C  ");
    Serial.print(tempF);
    Serial.println(" F");
  }

  delay(1000);
}

Code breakdown

• #include <OneWire.h> — provides the low-level 1-Wire protocol communication.
• #include <DallasTemperature.h> — provides the high-level API for DS18B20 sensors.
• OneWire oneWire(ONE_WIRE_BUS) — creates a OneWire instance on the specified pin.
• DallasTemperature sensors(&oneWire) — creates a DallasTemperature instance attached to the OneWire bus.
• sensors.begin() — initializes the library and discovers sensors on the bus.
• sensors.getDeviceCount() — returns the number of DS18B20 devices detected on the bus.
• sensors.requestTemperatures() — sends a conversion command to all sensors. This takes up to 750 ms at 12-bit resolution.
• sensors.getTempCByIndex(0) — returns the temperature in Celsius for the sensor at the given index (0-based, in discovery order).
• DEVICE_DISCONNECTED_C — constant (-127C) returned when the sensor is not responding.

Reading multiple sensors

To read from multiple DS18B20 sensors on the same bus, iterate by index:

for (int i = 0; i < sensors.getDeviceCount(); i++)
{
  float temp = sensors.getTempCByIndex(i);
  Serial.print("Sensor ");
  Serial.print(i);
  Serial.print(": ");
  Serial.println(temp);
}

Addressing a specific sensor by ROM address

For permanent installations where sensor order may change, address sensors by their unique 64-bit address:

DeviceAddress sensorAddr;

sensors.getAddress(sensorAddr, 0);
sensors.setResolution(sensorAddr, 12);

sensors.requestTemperatures();
float temp = sensors.getTempC(sensorAddr);

Steps to perform this interfacing

1. Connect the DS18B20 to the Arduino with a 4.7k ohm pull-up resistor on the data line.
2. Install the OneWire and DallasTemperature libraries via the Library Manager.
3. Copy the code into the Arduino IDE.
4. Select the correct board and port (Tools > Board and Tools > Port).
5. Upload the sketch to the Arduino.
6. Open the Serial Monitor (Tools > Serial Monitor, set baud rate to 9600).
7. Observe temperature readings printed every second.
8. (Optional) Connect additional DS18B20 sensors in parallel on the same data pin — they will be enumerated automatically.

Caution

• A 4.7k ohm pull-up resistor on the data line is required for 1-Wire communication to function. Without it, the sensor will not respond.
• Long cable runs (over 10 m / 30 ft) may require a lower pull-up resistor value (2.2k ohm - 4.7k ohm) and a 100 nF bypass capacitor at the sensor end.
• The conversion time depends on resolution: 9-bit = 94 ms, 10-bit = 188 ms, 11-bit = 375 ms, 12-bit = 750 ms. Allow sufficient time between requestTemperatures() and reading the value.
• When using parasitic power mode (GND and DATA only, no VCC), the data pin cannot drive the sensor during conversion. This mode is not recommended unless you fully understand the 1-Wire parasitic power constraints.
• The DS18B20 is not waterproof on its own. Use the stainless-steel probe version for outdoor, aquariums, or liquid temperature monitoring.
• Avoid bending the TO-92 package leads repeatedly — they can break off at the package body.