Introduction
The DS18B20 is a digital temperature sensor manufactured by Dallas Semiconductor, now a part of Maxim Integrated. It is widely used in hobbyist, industrial, and scientific applications due to its compact size, high resolution, and ease of integration with microcontrollers. The device delivers temperature measurements over a one‑wire interface, allowing multiple sensors to share a single data line while still maintaining unique identification through a 64‑bit serial address. It operates over a wide temperature range, typically from −55 °C to +125 °C, and offers a 12‑bit resolution, translating to 0.0625 °C increments.
Because the DS18B20 communicates digitally, it eliminates the need for analog-to-digital conversion stages that are common in other temperature sensing solutions. This feature simplifies system design and reduces cost. The sensor is available in various package types, including surface‑mount (SOT‑23‑5) and through‑hole (TSSOP). The following sections provide a comprehensive examination of the device, covering its historical context, technical specifications, application areas, and practical considerations for designers.
History and Development
Origins of Dallas Semiconductor
Dallas Semiconductor, founded in 1980, was a pioneer in one‑wire communication technology. The company introduced the first 1‑wire bus system in the early 1990s, targeting temperature and energy monitoring applications. The DS18S20, a 9‑bit resolution predecessor to the DS18B20, first appeared in 1994. Subsequent iterations improved accuracy, resolution, and power efficiency.
Introduction of the DS18B20
The DS18B20 entered the market in 2002. It was designed to provide higher resolution and improved accuracy compared to earlier models while maintaining the same low‑power, single‑wire communication protocol. Its adoption was accelerated by the proliferation of microcontroller platforms such as Arduino, Raspberry Pi, and ESP32, which could easily interface with the device via software libraries. The DS18B20 remains in production and continues to be a staple in temperature‑sensing circuits.
Physical Principles and Design
Sensing Element
The sensor’s core is a semiconductor thermistor, specifically a silicon di‑metallic resistor that exhibits a predictable change in resistance with temperature. The thermistor is embedded in a silicon substrate and is calibrated during manufacturing to match the datasheet specifications. The design allows for a linear relationship between resistance and temperature within the operational range.
Analog-to-Digital Conversion
The DS18B20 incorporates an internal analog-to-digital converter (ADC). After the thermistor’s voltage is sampled, the ADC converts the value to a digital representation at 12‑bit resolution. The ADC is clocked at a 3.125 kHz internal oscillator, ensuring that conversion takes a predictable amount of time. The resulting digital temperature code is stored in a temperature register, ready for retrieval over the bus.
Unique Addressing
Each DS18B20 contains a 64‑bit ROM address unique to the device. The address comprises a 48‑bit family code, a 48‑bit serial number, and a 8‑bit CRC for error detection. The address is transmitted during the ROM search sequence, allowing multiple sensors to coexist on the same bus without collision. The CRC is computed using a standard 8‑bit polynomial algorithm, facilitating robust error checking during communication.
Package Variants
Common DS18B20 packages include:
- SOT‑23‑5 (through‑hole) – 5 leads for supply, ground, data, and optional parasitic power
- SOT‑23‑5 (surface‑mount) – same pinout but for surface mounting
- TSSOP (through‑hole) – 8‑pin, provides a low profile for compact boards
Electrical and Communication Interfaces
Power Supply
The sensor operates on a supply voltage between 3.0 V and 5.5 V. Parasitic power mode is supported, allowing the device to draw power from the data line when a dedicated VDD line is not present. In parasitic mode, the sensor draws up to 125 µA during normal operation and up to 1 mA during temperature conversion, sufficient for many low‑power applications.
One‑Wire Protocol
The DS18B20 uses a one‑wire bus for communication. The protocol defines reset, presence detection, read/write slots, and data packet framing. Each byte is transmitted least significant bit first, and the bus is driven by a pull‑up resistor typically between 4.7 kΩ and 10 kΩ. The bus is designed to support up to 100 mA of current, allowing for multiple sensors and peripheral devices.
Timing Diagram and Commands
The device supports a set of standard commands:
- Read ROM (0x33) – retrieves the 64‑bit address
- Match ROM (0x55) – selects a particular device for subsequent commands
- Skip ROM (0xCC) – addresses all devices on the bus
- Convert T (0x44) – initiates temperature conversion
- Read Scratchpad (0xBE) – reads 9 bytes containing temperature, configuration, and CRC
- Write Scratchpad (0x4E) – writes temperature resolution configuration
- Copy Scratchpad (0x48) – copies RAM to EEPROM
- Recall EEPROM (0xB8) – restores settings from EEPROM
- Read Power Supply (0xB4) – checks for parasitic power mode
Each command sequence requires precise timing, with typical timeouts of 750 µs for reset and 15 ms for temperature conversion at maximum resolution.
Measurement Accuracy and Calibration
Resolution and Accuracy
The DS18B20 offers four selectable resolutions: 9 bit (0.5 °C), 10 bit (0.25 °C), 11 bit (0.125 °C), and 12 bit (0.0625 °C). The default is 12 bit. Accuracy is specified as ±0.5 °C over the full scale, improving to ±0.25 °C for the lower end of the range and to ±0.75 °C near the extremes.
Calibration Procedure
Manufacturing calibration ensures that the device meets the specified accuracy. For applications requiring higher precision, a user may perform in‑field calibration by comparing sensor output against a calibrated reference. Calibration typically involves recording the difference between sensor output and reference at several points, then adjusting the resolution or applying an offset in software.
Temperature Coefficient of Resistance (TCR)
The thermistor’s TCR is approximately 400 ppm/°C, which is relatively high compared to platinum RTDs. This high TCR allows for high sensitivity but requires careful handling of power dissipation to avoid self‑heating errors.
Noise and Stability
The sensor’s internal ADC is subject to Johnson–Nyquist noise, which is mitigated by the digital filtering inherent in the 12‑bit conversion. Long‑term drift is minimal, typically less than 0.01 °C per year, making the DS18B20 suitable for continuous monitoring applications.
Power Management and Consumption
Dynamic Power Modes
During idle periods, the DS18B20 enters a low‑power state, consuming less than 1 µA. When a temperature conversion is triggered, power consumption rises to approximately 125 µA in normal mode and up to 1 mA in parasitic mode. The device can be commanded to reduce resolution to save power; for instance, a 9‑bit conversion consumes roughly 50 % less current than a 12‑bit conversion.
Dynamic Power Table
- 9‑bit resolution: 125 µA
- 10‑bit resolution: 150 µA
- 11‑bit resolution: 175 µA
- 12‑bit resolution: 200 µA
These figures refer to normal power mode. In parasitic mode, each value is multiplied by approximately 4.
Battery‑Powered Applications
Because the DS18B20 can operate from a single 3.3 V or 5 V supply, it is ideal for battery‑powered devices such as remote weather stations. Careful scheduling of temperature conversion intervals can extend battery life; typical systems sample once every minute or less frequently, balancing accuracy with energy usage.
Typical Applications
Consumer Electronics
Smart thermostats, home automation hubs, and air‑conditioner controllers often integrate the DS18B20 to provide ambient temperature data. The sensor’s one‑wire interface allows for simplified wiring inside enclosures.
Industrial Monitoring
Process control systems, HVAC monitoring, and equipment health diagnostics utilize the DS18B20 for temperature monitoring of machinery. Its durability and accuracy make it suitable for harsh environments, provided that temperature extremes stay within the specified limits.
Environmental Sensors
Weather stations, greenhouse monitoring, and climate research stations employ DS18B20 sensors to gather temperature data. The low cost and widespread library support enable rapid prototyping of distributed sensor networks.
Embedded Systems
Microcontroller‑based projects such as Arduino and ESP32 hobby kits benefit from the DS18B20’s simple API. Many firmware examples exist, illustrating how to implement bus scanning, temperature conversion, and data logging.
Medical Devices
Non‑invasive temperature monitoring devices, such as wearable thermometers, use DS18B20 sensors for body‑temperature measurement. The sensor’s low power consumption and small size are advantageous for wearable form factors.
Automotive Applications
Vehicle interior climate control and engine temperature monitoring can incorporate DS18B20 sensors. The sensor’s resistance to vibration and electrical noise makes it a reliable choice for automotive environments.
Software and Libraries
Embedded Firmware
Many microcontroller platforms provide native libraries for the DS18B20. These libraries encapsulate the one‑wire protocol, provide bus scanning, and offer temperature conversion functions. Typical functions include:
- initializeBus()
- searchDevices()
- readTemperature(sensorAddress)
- setResolution(sensorAddress, resolution)
Operating System Support
Linux distributions often include a kernel driver that exposes DS18B20 sensors as files in the /sys/bus/w1 directory. Applications can read temperature values directly from the file system, simplifying integration with higher‑level software.
Programming Languages
Popular languages such as Python, C, and C++ have wrappers or libraries to interface with DS18B20 sensors. For instance, the Adafruit Unified Sensor library for Python includes classes to manage the bus and read temperature.
Calibration and Conversion Utilities
Utility functions are available to convert raw sensor codes to Celsius or Fahrenheit. Conversion formulas include:
- Celsius = (rawCode / 16) / 2resolution-12
- Fahrenheit = Celsius × 9/5 + 32
Troubleshooting and Common Issues
No Presence Pulse Detected
Possible causes include a broken data line, incorrect pull‑up resistor value, or damaged sensor. Verify continuity, ensure a pull‑up resistor between 4.7 kΩ and 10 kΩ, and check for proper supply voltage.
CRC Mismatch
When reading data, the CRC field may not match. Common reasons include electrical noise on the bus or insufficient pull‑up. Adding shielding, increasing the pull‑up resistance, or using a higher‑quality cable can resolve the issue.
Slow Conversion Time
Excessive conversion time can be caused by a high resolution setting or a faulty sensor. Reducing resolution from 12 bit to 9 bit cuts conversion time by approximately 75 %. Ensure the sensor’s temperature register is being read promptly.
Temperature Drift
Long‑term drift may indicate aging of the thermistor or improper calibration. Performing an in‑field calibration against a reference device can correct for drift.
Parasitic Power Failure
In parasitic mode, the sensor may fail to power if the data line does not provide sufficient current. Providing a dedicated VDD supply ensures reliable operation.
Future Trends
Integration into System‑on‑Chip
Emerging SoCs for IoT devices incorporate temperature sensing capabilities directly into the chip, reducing the need for discrete sensors. However, the DS18B20 remains relevant for applications requiring a robust, standalone sensor that can be replaced or added independently.
Higher Resolution Sensors
Newer sensors offering 14‑bit or 16‑bit resolution are entering the market, providing sub‑0.01 °C increments. These devices compete with the DS18B20 on accuracy and may replace it in high‑precision use cases.
Wireless Sensor Networks
Integrating DS18B20 sensors into low‑power wireless networks (e.g., Zigbee, Thread) enhances remote monitoring capabilities. Advances in ultra‑low‑power microcontrollers allow for longer battery life while maintaining frequent temperature updates.
Machine‑Learning‑Enabled Calibration
Software frameworks that automatically calibrate sensors based on environmental data can reduce the need for manual calibration. These systems may use historical temperature trends to refine sensor output over time.
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