How to Use DS18B20: Examples, Pinouts, and Specs

The DS18B20 is a digital temperature sensor manufactured by DS18B20. It communicates over a 1-Wire interface, requiring only one data line (and ground) for communication. This sensor provides temperature readings with a resolution of 9 to 12 bits and operates within a temperature range of -55°C to +125°C. Its compact design and ease of use make it ideal for a wide range of applications, including HVAC systems, weather monitoring, industrial temperature control, and home automation.

• Manufacturer: DS18B20
• Part ID: DS18B20
• Temperature Range: -55°C to +125°C
• Accuracy: ±0.5°C (from -10°C to +85°C)
• Resolution: Programmable from 9 to 12 bits
• Interface: 1-Wire
• Operating Voltage: 3.0V to 5.5V
• Current Consumption:
  • Active: 1 mA (typical)
  • Standby: 750 nA (typical)
• Response Time: <750 ms (12-bit resolution)
• Package Types: TO-92, SOIC, or waterproof probe

The DS18B20 typically comes in a 3-pin TO-92 package. Below is the pin configuration:

Note: The DS18B20 can operate in "parasite power mode," where it draws power from the data line (DQ) instead of requiring a dedicated VDD connection.

1. Wiring the Sensor:

   • Connect the GND pin to the ground of your circuit.
   • Connect the DQ pin to a digital I/O pin on your microcontroller.
   • Connect the VDD pin to a 3.3V or 5V power supply (or leave it unconnected for parasite power mode).
   • Place a 4.7 kΩ pull-up resistor between the DQ pin and the power supply (VDD). This is required for proper 1-Wire communication.

2. Communication Protocol:
   The DS18B20 uses the 1-Wire protocol, which allows multiple devices to share the same data line. Each sensor has a unique 64-bit serial code, enabling individual addressing.

3. Reading Temperature:

   • Send a "Convert T" command to initiate a temperature measurement.
   • Wait for the conversion to complete (up to 750 ms for 12-bit resolution).
   • Read the temperature data from the sensor's scratchpad memory.

• Use a decoupling capacitor (e.g., 0.1 µF) between VDD and GND to stabilize the power supply.
• Avoid long wires for the data line to minimize signal degradation. If long wires are necessary, consider using shielded cables.
• In parasite power mode, ensure the pull-up resistor is properly sized to provide sufficient current during temperature conversion.
• When using multiple DS18B20 sensors on the same bus, ensure each sensor's unique address is correctly identified.

Below is an example of how to interface the DS18B20 with an Arduino UNO using the popular OneWire and DallasTemperature libraries:

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

// Pin connected to the DS18B20 data line
#define ONE_WIRE_BUS 2

// Create a OneWire instance to communicate with the sensor
OneWire oneWire(ONE_WIRE_BUS);

// Pass the OneWire reference to DallasTemperature library
DallasTemperature sensors(&oneWire);

void setup() {
  Serial.begin(9600); // Initialize serial communication
  sensors.begin();    // Start the DS18B20 sensor
  Serial.println("DS18B20 Temperature Sensor Example");
}

void loop() {
  sensors.requestTemperatures(); // Request temperature measurement
  float temperatureC = sensors.getTempCByIndex(0); // Get temperature in Celsius

  // Check if the reading is valid
  if (temperatureC != DEVICE_DISCONNECTED_C) {
    Serial.print("Temperature: ");
    Serial.print(temperatureC);
    Serial.println(" °C");
  } else {
    Serial.println("Error: Sensor not detected!");
  }

  delay(1000); // Wait 1 second before the next reading
}

Explanation of the Code:

• The OneWire library handles communication with the DS18B20 over the 1-Wire protocol.
• The DallasTemperature library simplifies temperature measurement and data retrieval.
• The getTempCByIndex(0) function retrieves the temperature from the first sensor on the bus.

1. Sensor Not Detected:

   • Ensure the wiring is correct and the pull-up resistor is properly connected.
   • Verify that the data pin is connected to the correct Arduino pin.
   • Check for loose connections or damaged components.

2. Incorrect Temperature Readings:

   • Verify the power supply voltage is within the specified range (3.0V to 5.5V).
   • Ensure the pull-up resistor value is 4.7 kΩ.
   • Avoid placing the sensor near heat sources or in direct sunlight.

3. Multiple Sensors on the Same Bus Not Working:

   • Ensure each sensor's unique address is correctly identified in the code.
   • Use a separate pull-up resistor for each sensor if necessary.

Q1: Can the DS18B20 operate without a dedicated power supply?
Yes, the DS18B20 can operate in parasite power mode, drawing power from the data line. However, this mode may not work reliably in all setups, especially with long wires or multiple sensors.

Q2: What is the maximum cable length for the DS18B20?
The maximum cable length depends on factors such as wire quality, pull-up resistor value, and power supply. In general, lengths up to 30 meters are achievable with proper wiring and shielding.

Q3: How do I increase the resolution of the temperature readings?
The resolution (9 to 12 bits) can be configured by writing to the sensor's configuration register. Refer to the DS18B20 datasheet for detailed instructions.

Q4: Can the DS18B20 measure negative temperatures?
Yes, the DS18B20 can measure temperatures as low as -55°C. Negative temperatures are represented in two's complement format in the sensor's data output.