Application of DS18B20 Digital Temperature Sensor in Temperature Measurement

Photocoupler

1. Introduction

In modern industrial environments, accurate temperature monitoring and control are essential for maintaining efficiency and safety. The use of the 51 series microcontroller for temperature control offers advantages such as ease of programming, flexible configuration, and cost-effectiveness. This paper explores the practical application of the DS18B20 digital temperature sensor in real-world scenarios, highlighting its high accuracy and reliability. It is particularly suitable for industries like chemical production and power engineering, where precise temperature readings are critical.

2. Temperature Control System

The DS18B20, a digital temperature sensor from Dallas Semiconductor, converts measured temperatures into serial digital signals that can be easily processed by microcontrollers. With simple programming, it supports 9-bit temperature readings and allows multiple DS18B20 sensors to be connected via a single data line using the 1-Wire protocol. However, the AT89S51 microcontroller does not natively support this protocol, requiring software-based simulation of the 1-Wire timing for communication with the DS18B20.

The DS18B20 uses a time-sharing communication method, which requires strict timing constraints for both reading and writing operations. All interactions must follow a specific sequence: initialization (reset pulse), ROM command, memory operation command, and data processing. For example, within a 0–70°C range, the DS18B20 has an error margin of ±0.5°C, with typical accuracy reaching up to 0.25°C.

3. System Software Design

This section outlines the software implementation for the microcontroller, written in C language. It includes key components such as display functions, reset routines, read/write subroutines, and interrupt handling. Proper timing and synchronization are crucial for reliable communication with the DS18B20.

3.1 DS18B20 Software Design

The DS18B20 operates through a sequence of steps: initialization, ROM instruction, memory instruction, and data exchange. Each step involves precise timing, including the reset pulse, which lasts 500 microseconds. After a successful reset, the DS18B20 responds with a low pulse, allowing the microcontroller to proceed with further commands.

3.2 Writing Data to DS18B20

Data writing requires the host to pull the data line low, generating two types of write pulses: one for '1' and another for '0'. Both pulses must last at least 60 microseconds, with a recovery time of at least 1 microsecond between cycles. For a '0' write, the bus must remain low for at least 60 microseconds, while a '1' write requires the bus to return to high within 15 microseconds.

3.3 Reading Data from DS18B20

To read data, the host initiates a read sequence by pulling the data line low. The DS18B20 outputs valid data for 15 microseconds after the falling edge. The host must sample the data during this window and then release the line, allowing it to return to high via an external pull-up resistor. All read operations must also follow strict timing rules.

3.4 Interrupt Service Program Design

Interrupts allow the microcontroller to respond to urgent events without halting the main program. When an interrupt occurs, the CPU pauses its current task, processes the interrupt, and returns to the original task. This is essential for real-time systems where timely responses are required. The AT89C51 microcontroller supports interrupts based on specific conditions, such as enabling the interrupt source and setting the global interrupt flag (EA = 1).

3.5 Main Program Flowchart

The system starts with initialization, followed by a reset and detection signal. If a signal is detected, the microcontroller reads the data from the DS18B20 and displays the result on a seven-segment display. The entire process must adhere to strict timing requirements to ensure accurate and stable operation.

4. Conclusion

This paper presents a comprehensive temperature monitoring system that integrates advanced information processing techniques and single-bus communication. By using modular design and the 1-Wire protocol, the system ensures efficient and accurate temperature readings. Its real-time capabilities enable early problem detection and prompt corrective actions, making it ideal for applications requiring high precision and reliability.