Open the editorEditor
Arduino Uno · DS18B20

Arduino Uno DS18B20 Simulator: Wiring, Code and a Live Circuit

This is a DS18B20 digital temperature sensor wired to an Arduino Uno with its 4.7 k pull-up, read live with the OneWire and DallasTemperature libraries: one reading a second, to a hundredth of a degree.

Three legs and one resistor: VDD to 5V, GND, and DQ to pin 2 with the pull-up from DQ to 5V. In the editor, drag the sensor’s temperature slider and the next reading follows.

Run it in the editorRead the code
  • 5 V logic
  • Library: DallasTemperature.h
  • DQ on pin 2
  • 4.7 k pull-up
Arduino Uno · DS18B20live0.000 s 0.00x
Click to open it in the editor
The circuit itself, running on the simulator with the sketch below. Press what can be pressed; click anything else to open it in the editor.

Wiring the DS18B20 to the Arduino Uno

Every connection in the circuit above, with the board’s own pin names.

DS18B20 pinArduino Uno pinWhy
VDD (right leg)5VThe DS18B20 runs from 3.0 to 5.5 V.
DQ (middle leg)pin 2The one data wire, shared by every sensor on the bus.
GND (left leg)GNDGround, with the flat face toward you.
4.7 k resistorDQ to 5VThe pull-up the bus needs: the sensor only ever pulls the line low.

On the Arduino Uno the sensor and its pull-up go to 5V. A long cable may need a stronger pull-up, 2.2 k, to keep the edges sharp.

Pins to leave alone on the Arduino Uno

Pins 0 and 1 are the USB serial port on a real Uno, so anything wired there fights the upload and the serial monitor. Pin 13 carries the onboard LED.

On a real bench

On a real bench the Uno stands beside the breadboard: the DS18B20 goes into the breadboard and male-to-male jumpers run from the Uno’s female headers to its rows. Power the Uno from USB while you build, and unplug it before you move a wire.

The code

The sketch the circuit above runs. Open it in the editor, change a line and press Run: it compiles in your browser.

DS18B20 on Arduino Uno pin 2
#include <OneWire.h>
#include <DallasTemperature.h>

const int ONE_WIRE_PIN = 2;   // DQ, pin 2, with 4.7 k to 5V

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 conversion on every sensor
  float celsius = sensors.getTempCByIndex(0);
  if (celsius == DEVICE_DISCONNECTED_C) {
    Serial.println("Sensor not found");
  } else {
    Serial.print("Temperature: ");
    Serial.print(celsius, 2);
    Serial.println(" C");
  }
  delay(1000);
}

OneWire oneWire(ONE_WIRE_PIN) runs the 1-Wire protocol on the pin, and DallasTemperature sensors(&oneWire) speaks to DS18B20s over it. sensors.begin() searches the bus, and getDeviceCount() says how many sensors answered.

requestTemperatures() starts a conversion on every sensor at once and waits for it: 750 ms at the default 12 bits. getTempCByIndex(0) then reads the first sensor found. DEVICE_DISCONNECTED_C, -127, means no sensor answered.

Each DS18B20 has a unique 64-bit address, so several can share this one pin. Serial.begin(9600) opens the serial monitor. Serial goes over the USB cable, and the serial monitor in the editor reads it at whatever baud rate the sketch sets.

Common mistakes with the DS18B20 on the Arduino Uno

No pull-up resistor

Without the 4.7 k from DQ to the supply, the line never goes high, sensors.begin() finds nothing and every reading is -127. In the simulator, delete the resistor and you get exactly that.

The sensor in backwards

With the flat side facing you, the legs are GND, DQ, VDD from left to right. Reversed, a real DS18B20 gets hot fast. Waterproof probes use red for VDD, black for GND and yellow or white for DQ.

Using pins 0 and 1

Pins 0 and 1 carry the USB serial port on a real Uno. the 1-Wire bus wired there fights every upload and every Serial.print(). Start at pin 2.

Questions and answers

Can I simulate a DS18B20 with an Arduino Uno?

Yes. The circuit at the top of this page is an Arduino Uno with a DS18B20, running in your browser on a simulated ATmega328P. The simulated sensor speaks real 1-Wire, timing and addresses included, so the libraries run unchanged. Press Run it in the editor to change the wiring or the code; it is free and needs no account.

Why do I get -127?

That is DEVICE_DISCONNECTED_C: no sensor answered. The pull-up is missing, DQ is on a different pin from the sketch, or the sensor is wired backwards.

Can I connect several DS18B20s to one pin?

Yes. Wire them all in parallel to pin 2, with one pull-up for the bus, and read each with getTempCByIndex(0), (1) and so on, or by its address.

What is parasite power?

A mode where VDD is tied to GND and the sensor draws power from the data line through the pull-up. It saves a wire but needs a strong pull-up during conversions; three wires, as here, is more reliable.

Build your own DS18B20 project

Open this circuit in the editor, change the wiring or the code, and keep your version in a free account.

Start building freeOpen the editor