Verify a DS18B20 conversion

Discover one addressed DS18B20, wait for its 12-bit conversion, and verify positive and negative readings without accepting protocol error values.

Physics Phoebe: I want you to prove identity and conversion completion before trusting the temperature., your practice guide

Physics Phoebe: I want you to prove identity and conversion completion before trusting the temperature.
Predict the reading, then compare it with the measurement.

Wokwi ESP32

Third party Tool

Discover one addressed DS18B20, wait for its 12-bit conversion, and verify positive and negative readings without accepting protocol error values.

Tier 1 · Web · No account

Version tested: Compiled and booted by the Wokwi gate (ESP32 Arduino core 3.3.11); captured in the Wokwi web editor on 2026-09-09. Date: 2026-09-09.

Open the ESP32 editor, paste diagram.json, then paste sketch.ino.

Open Wokwi to paste in the files (new tab)

Get the files

Use both prepared files. This is a paste-in setup; saving a project requires a Wokwi account.

diagram.json

774 bytes · Circuit connections

Download

sketch.ino

1,282 bytes · ESP32 program

Download

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

constexpr uint8_t ONE_WIRE_PIN = 4;
constexpr uint16_t CONVERSION_MS_12_BIT = 750;
OneWire oneWire(ONE_WIRE_PIN);
DallasTemperature sensors(&oneWire);
DeviceAddress address;

void printAddress(const DeviceAddress value) {
  for (uint8_t i = 0; i < 8; i++) {
    if (value[i] < 16) Serial.print('0');
    Serial.print(value[i], HEX);
  }
}

void setup() {
  Serial.begin(115200);
  sensors.begin();
  sensors.setResolution(12);
  sensors.setWaitForConversion(false);

const uint8_t count = sensors.getDeviceCount();
  Serial.printf("ONEWIRE FOUND count=%u pin=4 pullup=4.7k\n", count);
  if (count == 1 && sensors.getAddress(address, 0)) {
    Serial.print("ONEWIRE ADDRESS ");
    printAddress(address);
    Serial.println();
  } else {
    Serial.println("ONEWIRE ERROR expected-one-sensor");
  }
}

void loop() {
  sensors.requestTemperatures();
  Serial.println("CONVERT requested resolution=12bit wait=750ms");
  delay(CONVERSION_MS_12_BIT);
  const float temperature = sensors.getTempC(address);
  if (temperature == DEVICE_DISCONNECTED_C) {
    Serial.println("TEMP status=DISCONNECTED sample-discarded");
  } else {
    Serial.printf("TEMP value=%.2fC status=VALID conversion=750ms\n", temperature);
  }
  delay(250);
}

Use the launch button above to open the ESP32 editor in Wokwi.
Select the editor’s diagram.json tab and replace all its text with the supplied diagram.json.
Select the sketch.ino tab, replace all its text with the supplied sketch.ino, then click Start Simulation.

Steps

Screens captured against Wokwi ESP32 Compiled and booted by the Wokwi gate (ESP32 Arduino core 3.3.11); captured in the Wokwi web editor on 2026-09-09 on 2026-09-09; the tool may have moved on — the text steps are the contract.

Step 1
Do
Paste diagram.json and sketch.ino into a new Wokwi ESP32 project, then trace the 1-Wire circuit.
You will see
The DS18B20 data pin reaches GPIO4 and a 4.7 kOhm resistor pulls the shared line to 3.3 V.
Why it matters
The pull-up is part of the digital bus, so discovery evidence is invalid if it is omitted.
Step 2
Do
Inspect device discovery, the nonblocking conversion request, and the 750 ms wait.
You will see
The sketch confirms exactly one address, requests 12-bit conversion, waits 750 ms, and rejects the disconnected sentinel.
Why it matters
Address, conversion completion, and validity are separate protocol claims that should remain visible.
Step 3
Do
Start the simulation and read the bus discovery line.
You will see
ONEWIRE FOUND reports one sensor on GPIO4 with the 4.7 kOhm pull-up.
Why it matters
Counting devices before indexing them prevents an absent sensor from becoming a plausible-looking temperature.
Step 4
Do
Read the discovered sensor's ROM code.
You will see
The sketch prints one 64-bit hexadecimal address.
Why it matters
A stored address is what lets firmware associate a reading with one physical position on a shared bus.
Step 5
Do
Leave the sensor at 24 degrees C and inspect the request and result.
You will see
After the declared 750 ms conversion wait, the result is 24.00 degrees C with status VALID.
Why it matters
The result is accepted only after the resolution-dependent conversion time has elapsed.
Step 6
Do
Select the DS18B20 and set its temperature to 30 degrees C.
You will see
The next completed conversion reports 30.00 degrees C with status VALID.
Why it matters
A controlled positive change checks that new data follows a fresh conversion instead of a cached startup value.
Step 7
Do
Set the DS18B20 temperature to -7 degrees C.
You will see
The next completed conversion reports -7.00 degrees C with status VALID.
Why it matters
A negative test checks signed temperature handling rather than treating the raw word as unsigned.

Chapter checks

These questions refer to the chapter’s examples. Use the return links to review their answers.

Several DS18B20 sensors share one GPIO. What lets the controller distinguish their readings?
Return to the chapter’s knowledge check
The lab sensor returns the documented incomplete-conversion value. What should the firmware check?
Return to the chapter’s knowledge check

Return to Temperature Sensor Labs: Comparing Sensor Types · Browse Labs

Wokwi ESP32

Get the files

diagram.json

sketch.ino

Steps

1 Step 1

2 Step 2

3 Step 3

4 Step 4

5 Step 5

6 Step 6

7 Step 7

Chapter checks

Step 1

Step 2

Step 3

Step 4

Step 5

Step 6

Step 7