Tutorial 17: DS18B20 Digital Temperature Sensor Guide

Introduction to DS18B20

The DS18B20 is a popular digital temperature sensor from Maxim Integrated (now Analog Devices). Unlike the DHT22, it measures temperature only (no humidity), but offers excellent accuracy, a wide temperature range, and a unique feature: multiple sensors can share the same data pin!

Pinout and Wiring

The DS18B20 comes in two common form factors: TO-92 transistor package (3 pins) and waterproof probe (3 wires).

TO-92 Package (Through-Hole)

DS18B20 TO-92 Pinout (flat side facing you, pins down):
            
    ┌─────────────────┐
    │   ┌─────────┐   │
    │   │ DS18B20 │   │
    │   └─────────┘   │
    │                 │
    │  ┌───┐ ┌───┐   │
    │  │ 1 │ │ 2 │   │  ← Pin 1: GND, Pin 2: DATA
    │  └───┘ └───┘   │
    │      ┌───┐     │
    │      │ 3 │     │  ← Pin 3: VDD
    │      └───┘     │
    └─────────────────┘

Waterproof Probe Version

DS18B20 Wiring with 4.7kΩ Pull-up Resistor:

    3.3V ──────┬────────────────────── VDD (Pin 3 / Red)
               │
              4.7kΩ
               │
    GPIO ──────┼────────────────────── DATA (Pin 2 / Yellow)
               │
               │
    GND ───────┴────────────────────── GND (Pin 1 / Black)

Wiring to ESP8266 (D1 Mini)

ESP8266 D1 Mini + DS18B20 Wiring:
┌─────────┐                    ┌──────────┐
│ D1 Mini │                    │ DS18B20  │
├─────────┤                    ├──────────┤
│   3.3V  ├────┬───────────────┤ VDD (3)  │
│         │    │               │          │
│    D2   ├────┼───────────────┤ DATA (2) │
│         │    │    4.7kΩ      │          │
│   GND   ├────┼────[====]─────┤ GND (1)  │
│         │    │               │          │
└─────────┘    │               └──────────┘
               └────────────────┘

Wiring to ESP32

Wiring to Raspberry Pi Pico W

Installing Required Libraries

DS18B20 requires two libraries: OneWire (communication protocol) and DallasTemperature (high-level functions).

1. Open Arduino IDE
2. Go to Sketch → Include Library → Manage Libraries
3. Search for "OneWire"
4. Find "OneWire by Jim Studt" (or Paul Stoffregen version) and click Install
5. Search for "DallasTemperature"
6. Find "DallasTemperature by Miles Burton" and click Install

Testing Your DS18B20

Before flashing the full OceanRemote firmware, test your DS18B20 with this simple sketch:

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

#define ONE_WIRE_BUS 4    // Change to your GPIO pin (ESP8266 D2 = GPIO4)

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

void setup() {
  Serial.begin(115200);
  sensors.begin();
  Serial.println("DS18B20 Test Started");
}

void loop() {
  sensors.requestTemperatures();
  float temp = sensors.getTempCByIndex(0);
  
  if (temp == -127.0) {
    Serial.println("DS18B20 read failed! Check wiring and pull-up resistor.");
  } else {
    Serial.print("Temperature: ");
    Serial.print(temp);
    Serial.println("°C");
  }
  delay(2000);
}

Multiple DS18B20 Sensors on One Pin

The DS18B20's superpower is that you can connect multiple sensors to the same GPIO pin. Each sensor has a unique 64-bit ROM address, and the library automatically detects all connected sensors.

Wiring Multiple DS18B20 Sensors (Parasite Mode Not Recommended):
            
    3.3V ──────┬──────────────────────────────────────┐
               │                                      │
              4.7kΩ                                   4.7kΩ
               │                                      │
    GPIO ──────┼──────────────────────────────────────┼──────┐
               │                                      │      │
               │                    ┌──────────┐     │      │
               │                    │ DS18B20  │     │      │
               │                    │    #1    │     │      │
               │                    └──────────┘     │      │
               │                         │           │      │
               │                    ┌──────────┐     │      │
               │                    │ DS18B20  │     │      │
               │                    │    #2    │     │      │
               │                    └──────────┘     │      │
               │                         │           │      │
    GND ───────┴─────────────────────────┴───────────┴──────┘

Detecting Multiple Sensors

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

#define ONE_WIRE_BUS 4
OneWire oneWire(ONE_WIRE_BUS);
DallasTemperature sensors(&oneWire);

void setup() {
  Serial.begin(115200);
  sensors.begin();
  
  int deviceCount = sensors.getDeviceCount();
  Serial.print("Found ");
  Serial.print(deviceCount);
  Serial.println(" DS18B20 sensors");
  
  for (int i = 0; i < deviceCount; i++) {
    DeviceAddress address;
    sensors.getAddress(address, i);
    Serial.print("Sensor ");
    Serial.print(i);
    Serial.print(" Address: ");
    printAddress(address);
  }
}

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

void loop() {
  sensors.requestTemperatures();
  
  int deviceCount = sensors.getDeviceCount();
  for (int i = 0; i < deviceCount; i++) {
    float temp = sensors.getTempCByIndex(i);
    Serial.print("Sensor ");
    Serial.print(i);
    Serial.print(": ");
    Serial.print(temp);
    Serial.println("°C");
  }
  
  delay(2000);
}

How OceanRemote Uses DS18B20

When you select DS18B20 in the device configuration, OceanRemote firmware automatically:

• Initializes the OneWire bus on the specified pin
• Searches for the first DS18B20 sensor (index 0)
• Reads temperature every 5 seconds
• Sends the temperature value to the server with each poll
• Displays temperature on your dashboard
• Allows temperature calibration via offset (dashboard setting)

// How OceanRemote reads DS18B20 (firmware snippet)
#include <OneWire.h>
#include <DallasTemperature.h>

#define ONE_WIRE_BUS 4    // GPIO4 on ESP8266 (D2)
OneWire oneWire(ONE_WIRE_BUS);
DallasTemperature sensors(&oneWire);

void setupSensor() {
  sensors.begin();
}

void readSensor() {
  static unsigned long lastRead = 0;
  unsigned long now = millis();
  
  if (now - lastRead >= 5000) {
    lastRead = now;
    sensors.requestTemperatures();
    float temp = sensors.getTempCByIndex(0);
    
    if (temp == -127.0 || temp == 85.0) {
      temperature = -999;  // Invalid reading
    } else {
      temperature = temp;
    }
  }
}

Calibrating DS18B20 Readings

OceanRemote allows you to calibrate temperature readings using an offset. The DS18B20 is quite accurate (±0.5°C), but calibration can correct for installation-specific errors.

How to Calibrate:

1. Place a known-accurate thermometer next to your DS18B20
2. Note the difference between the two readings
3. In your OceanRemote dashboard, find your device's temperature card
4. Enter the offset value in the "Calibration Offset (±°C)" field
5. The formula is: Calibrated = Raw Reading + Offset

Example:
Raw reading: 23.5°C
Actual temperature: 22.8°C
Difference: -0.7°C
Enter offset: -0.7

Result: 23.5 + (-0.7) = 22.8°C ✓

Parasite Mode (Advanced)

The DS18B20 can operate in "parasite mode" where it draws power from the DATA line, eliminating the need for a separate VDD connection. This is useful for 2-wire installations.

Troubleshooting DS18B20

Problem: Temperature reads -127°C

• Most likely: Missing or incorrect pull-up resistor! Add 4.7kΩ between DATA and 3.3V.
• Check wiring - DATA must be connected to the correct GPIO pin
• Verify VDD is connected to 3.3V or 5V
• Try a different GPIO pin

Problem: Temperature reads 85°C

• This is the power-on reset value of the DS18B20
• Usually means the sensor is powered but communication is failing
• Check DATA connection and pull-up resistor value
• Try a shorter cable (long cables can cause signal issues)

Problem: Erratic or jumping readings

• Check pull-up resistor (4.7kΩ is recommended)
• Check for loose connections
• Avoid running DATA wire near power lines (60Hz interference)
• For long cables (>10m), use a lower pull-up value (2.2kΩ) and shielded cable

Problem: No sensors found

• Run the address detection sketch to verify sensor is responding
• Check that VDD is getting power (3.3V or 5V)
• Verify pull-up resistor is installed
• Try a different DS18B20 (sensor may be damaged)

DS18B20 Best Practices

• Pull-up Resistor: Always use a 4.7kΩ resistor between DATA and VCC. This is not optional!
• Waterproof Version: Great for aquariums, outdoor sensors, refrigerators, and soil temperature monitoring.
• Cable Length: Keep wires under 10-20 meters for reliable communication. Use shielded cable for longer runs.
• Multiple Sensors: You can connect dozens of DS18B20 sensors to one pin! Each has a unique address.
• Power: Use 3.3V for consistency with ESP boards, or 5V if needed (both work).
• Resolution: Default 12-bit resolution gives 0.0625°C precision. OceanRemote uses default settings.

Next Steps

Now that you understand the DS18B20 sensor, continue with:

• Tutorial 18: NTC 10kΩ Thermistor Guide
• Tutorial 19: Understanding the NTC Voltage Divider Circuit
• Tutorial 20: Calibrating Temperature Sensors with Offset
• Return to Tutorial 02: Generate firmware with DS18B20 support!