DS18B20 1-Wire Digital Temperature Sensor – Pinout, Features, and Applications

Introduction to the DS18B20 Temperature Sensor

The DS18B20 is a digital thermometer that provides 9-bit to 12-bit Celsius temperature measurements. It communicates over a 1-Wire bus, which by definition requires only one data line (and ground) for communication with a central microprocessor. The sensor has an operating temperature range of -55°C to +125°C and is accurate to ±0.5°C over the range of -10°C to +85°C.

Key Features of the DS18B20

• Unique 1-Wire interface requires only one port pin for communication
• Each device has a unique 64-bit serial code stored in an onboard ROM
• Multidrop capability simplifies distributed temperature sensing applications
• Requires no external components
• Can be powered from data line (power supply range is 3.0V to 5.5V)
• Measures temperatures from -55°C to +125°C (-67°F to +257°F)
• ±0.5°C accuracy from -10°C to +85°C
• Temperature-limit alarm system
• Selectable resolution from 9 to 12 bits
• Converts temperature to 12-bit digital word in 750ms (max.)

DS18B20 Pinout and Wiring

The DS18B20 temperature sensor comes in various packages, including TO-92, SO, and µSOP. The most common package is the TO-92, which resembles a small transistor. Below is the pinout for the TO-92 package:

To connect the DS18B20 to a microcontroller, you will need to use a pull-up resistor (typically 4.7kΩ) between the data line and the power supply. This resistor is necessary for proper communication between the sensor and the microcontroller.

Wiring Example with Arduino

Here’s an example of how to wire the DS18B20 to an Arduino:

1. Connect the GND pin of the DS18B20 to the GND pin on the Arduino.
2. Connect the VDD pin of the DS18B20 to the 5V pin on the Arduino.
3. Connect the DQ pin of the DS18B20 to a digital pin on the Arduino (e.g., pin 2).
4. Place a 4.7kΩ pull-up resistor between the DQ pin and the VDD pin.

Communicating with the DS18B20

The DS18B20 uses the 1-Wire protocol for communication, which allows multiple devices to be connected to a single data line. Each DS18B20 has a unique 64-bit serial code, allowing the microcontroller to identify and communicate with individual sensors on the 1-Wire bus.

1-Wire Protocol Overview

The 1-Wire protocol uses a single data line for communication, along with a ground reference. The data line is bidirectional, meaning that both the microcontroller and the DS18B20 can transmit and receive data. The communication follows a master-slave model, where the microcontroller initiates all transactions and the DS18B20 responds accordingly.

The 1-Wire protocol consists of several key operations:

• Reset: The master device initiates communication by sending a reset pulse, which synchronizes all devices on the bus.
• ROM commands: These commands allow the master to identify, select, and address specific devices on the 1-Wire bus.
• Function commands: These commands are used to read from or write to the DS18B20’s scratchpad memory, initiate temperature conversions, and configure the sensor’s settings.

Communicating with Multiple DS18B20 Sensors

One of the key advantages of the 1-Wire protocol is the ability to connect multiple devices to a single data line. This is particularly useful when working with multiple DS18B20 sensors, as it allows you to monitor temperatures at various locations using minimal wiring.

To communicate with multiple DS18B20 sensors, you will need to use the ROM commands to identify and select each sensor individually. The process typically involves the following steps:

1. Send a reset pulse to synchronize all devices on the bus.
2. Issue the “Search ROM” command to discover the unique 64-bit addresses of all connected sensors.
3. Select a specific sensor by sending the “Match ROM” command followed by its unique address.
4. Communicate with the selected sensor using function commands (e.g., initiate a temperature conversion, read the temperature value).
5. Repeat steps 3 and 4 for each additional sensor on the bus.

Configuring and Reading Temperature Data

The DS18B20 stores temperature data and configuration settings in its scratchpad memory. The scratchpad memory consists of nine bytes, which include the temperature value, temperature alarm settings, and configuration data.

Temperature Conversion

To read the current temperature from the DS18B20, you must first initiate a temperature conversion. This is done by sending the “Convert T” function command to the sensor. The conversion time depends on the selected resolution, with higher resolutions requiring more time:

After initiating the temperature conversion, you can either wait for the conversion to complete or use the 1-Wire bus for other tasks and check the conversion status later.

Reading Temperature Data

Once the temperature conversion is complete, you can read the temperature value from the DS18B20’s scratchpad memory. This is done by sending the “Read Scratchpad” function command, which returns all nine bytes of the scratchpad, including the temperature value.

The temperature value is stored as a 16-bit signed integer in two’s complement format. The lower 4 bits of the temperature value represent the fractional part of the temperature, with a resolution of 0.0625°C per bit. To convert the raw temperature data to degrees Celsius, you can use the following formula:

Temperature (°C) = (Temp_MSB << 8 | Temp_LSB) / 16

Where Temp_MSB is the most significant byte of the temperature value, and Temp_LSB is the least significant byte.

Configuring Temperature Alarms

The DS18B20 includes a temperature alarm system that allows you to set high and low temperature thresholds. When the measured temperature exceeds the high threshold or falls below the low threshold, the sensor sets an alarm flag in the scratchpad memory.

To configure the temperature alarm settings, you need to write the desired threshold values to the appropriate bytes in the scratchpad memory using the “Write Scratchpad” function command.

Applications of the DS18B20 Temperature Sensor

The DS18B20 temperature sensor is widely used in various applications due to its accuracy, reliability, and ease of use. Some common applications include:

1. Environmental monitoring: The DS18B20 can be used to monitor temperatures in indoor and outdoor environments, such as greenhouses, data centers, and weather stations.

2. Industrial process control: In industrial settings, the DS18B20 can help monitor and control the temperature of liquids, gases, and solid materials, ensuring optimal process conditions and product quality.

3. Home automation: The sensor can be integrated into smart home systems to monitor and control the temperature of rooms, water tanks, and appliances, enabling energy-efficient operation and improved comfort.

4. Medical and healthcare: The DS18B20 can be used in medical devices and equipment to monitor patient body temperature, as well as in laboratory equipment to ensure proper storage conditions for sensitive materials.

5. Automotive and transportation: In vehicles, the sensor can monitor the temperature of engine coolant, exhaust gases, and cabin air, contributing to improved performance, fuel efficiency, and passenger comfort.

Conclusion

The DS18B20 1-Wire digital temperature sensor is a versatile and reliable choice for a wide range of temperature sensing applications. Its unique 1-Wire interface, high accuracy, and multi-drop capability make it an attractive option for projects requiring distributed temperature monitoring. By understanding the sensor’s pinout, communication protocol, and configuration options, you can easily integrate the DS18B20 into your designs and develop efficient temperature monitoring solutions.

Frequently Asked Questions (FAQ)

1. Q: What is the operating voltage range of the DS18B20?
   A: The DS18B20 can operate with a power supply ranging from 3.0V to 5.5V.

2. Q: How many DS18B20 sensors can be connected to a single 1-Wire bus?
   A: The number of DS18B20 sensors that can be connected to a single 1-Wire bus is theoretically unlimited, but practical limitations, such as bus capacitance and power supply, may restrict the number of devices.

3. Q: What is the maximum distance over which the DS18B20 can communicate?
   A: The maximum distance depends on varios factors, such as the wire gauge, the presence of noise, and the number of devices on the bus. In general, the 1-Wire bus can support distances up to 300 meters using twisted pair wiring.

4. Q: Can the DS18B20 be used to measure temperatures below -55°C or above +125°C?
   A: No, the DS18B20 is designed to operate within the temperature range of -55°C to +125°C. Exposing the sensor to temperatures outside this range may damage the device or result in inaccurate readings.

5. Q: How can I interface the DS18B20 with a Raspberry Pi?
   A: To interface the DS18B20 with a Raspberry Pi, you can connect the sensor’s VDD pin to the 3.3V pin on the Pi, the GND pin to a ground pin, and the DQ pin to a GPIO pin (e.g., GPIO4). Remember to use a 4.7kΩ pull-up resistor between the DQ pin and the VDD pin. You can then use the 1-Wire library in Python to communicate with the sensor.