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ESP32-S3 · DS18B20

ESP32-S3 DS18B20 Simulator: Wiring, Code and a Live Circuit

This is a DS18B20 digital temperature sensor wired to an ESP32-S3 DevKitC-1 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 3V3, GND, and DQ to GPIO 4 with the pull-up from DQ to 3V3. In the editor, drag the sensor’s temperature slider and the next reading follows.

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  • 3.3 V logic
  • Library: DallasTemperature.h
  • DQ on GPIO 4
  • 4.7 k pull-up
ESP32-S3 · DS18B20live0.000 s 0.00x
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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 ESP32-S3

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

DS18B20 pinESP32-S3 pinWhy
VDD (right leg)3V3The DS18B20 runs from 3.0 to 5.5 V.
DQ (middle leg)GPIO 4The one data wire, shared by every sensor on the bus.
GND (left leg)GGround, with the flat face toward you.
4.7 k resistorDQ to 3V3The pull-up the bus needs: the sensor only ever pulls the line low.

On the ESP32-S3 the sensor and its pull-up go to 3V3, so the data line idles at 3.3 V. With a long cable, drop the pull-up to 2.2 k.

Pins to leave alone on the ESP32-S3

GPIO 19 and 20 are the USB port’s data lines, GPIO 35 to 37 belong to the PSRAM on octal-PSRAM boards such as the N8R8, and GPIO 0, 3, 45 and 46 are strapping pins.

On a real bench

The DevKitC-1 has two USB sockets: UART for uploading and the serial monitor, USB for the S3’s own USB device. Plug into UART while you work with the DS18B20. The board is wide, so a single breadboard leaves only one row free on one side.

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 ESP32-S3 GPIO 4
#include <OneWire.h>
#include <DallasTemperature.h>

const int ONE_WIRE_PIN = 4;   // DQ, GPIO 4, with 4.7 k to 3V3

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

void setup() {
  Serial.begin(115200);
  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(115200) opens the serial monitor. Serial is UART0 on the board’s UART socket, at 115200 baud in this sketch.

Common mistakes with the DS18B20 on the ESP32-S3

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 the USB or PSRAM pins

GPIO 19 and 20 are the USB port’s data lines and GPIO 35 to 37 belong to the PSRAM on N8R8 boards. Wire the 1-Wire bus to one of those and the USB socket or the memory stops working on a real board, even though the simulator carries on. Stay on GPIO 4 to 18.

Questions and answers

Can I simulate a DS18B20 with an ESP32-S3 DevKitC-1?

Yes. The circuit at the top of this page is an ESP32-S3 DevKitC-1 with a DS18B20, running in your browser on a simulated ESP32-S3 (Xtensa LX7). 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 GPIO 4, 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.

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