Abstract: The existing traditional temperature and humidity monitoring systems have been studied and found that they mostly use RS485 transmission mode, which has limitations such as small control range and complicated wiring. In order to build a large-scale cross-regional temperature and humidity monitoring system, the method of combining Ethernet technology with traditional temperature and humidity monitoring system and the idea of ​​hardware and software co-design are adopted to develop a modular and scalable distributed intelligent temperature and humidity monitoring system based on Ethernet. Practice has proved that the system has a large control range and utilizes the existing developed network without rewiring, which can effectively realize remote temperature and humidity monitoring. The overall structure of the system and the working principle of each part are explained in detail in this paper. Keywords: temperature and humidity monitoring; remote control; Ethernet; distributed 1 Introduction Many large enterprises now have multiple warehouses scattered in different locations, which is not conducive to unified management; how to use the widely used Ethernet to transform the traditional temperature and humidity monitoring system based on RS485 bus to build a large-scale remote distributed temperature and humidity monitoring system[1] has become an urgent issue to be solved. This paper proposes a remote distributed intelligent temperature and humidity monitoring system based on existing Ethernet, which is easy to install, requires no rewiring, and is easy to install. The paper details the overall structure and working principle of the system. The system adopts a modular design and can be slightly modified to adapt to a multi-point distributed remote intelligent temperature and humidity monitoring system suitable for various occasions. 2 Hardware System Design and Implementation 2.1 Overall System Composition Each temperature and humidity monitor consists of a microcontroller, temperature sensor, humidity sensor, DS1302, LED digital tube display module, address DIP module, external memory, buzzer, air conditioner, dehumidifier, humidifier, etc. 128 temperature and humidity monitors with independent addresses are connected in parallel via an RS485 bus, and can directly communicate with the microcomputer via an RS485 to TCP/IP protocol converter to form a unit temperature and humidity monitoring system (see Figure 1 for the structure diagram of the unit temperature and humidity monitoring system). [align=center] Figure 1 Unit Temperature and Humidity Monitoring System Structure Diagram[/align] Several unit temperature and humidity monitoring systems can be combined through a hub to form a complete remote distributed intelligent temperature and humidity monitoring system (see Figure 2 for the overall system structure diagram). [align=center] Figure 2 Overall System Structure Diagram[/align] 2.2 Composition and Implementation of the Specific Temperature and Humidity Monitor A specific temperature and humidity monitor consists of an AT89C52 microcontroller with an external clock module, temperature measurement module, humidity measurement module, LED display module, external storage module, address module, air conditioner, humidifier, and dehumidifier driver modules. 2.2.1 MCU Module Each temperature and humidity monitor uses the AT89C52 8-bit microcontroller from Atmel Corporation, USA; it contains 8K bytes of rewritable read-only program memory and 256 bytes of random access data memory. 2.2.2 The DS1302 clock module adds dual power supply pins for main power and backup power, and provides the ability to trickle charge the backup power so that the battery can continue to save time information and data when the main power fails. The connection between the DS1302 and the CPU only requires three lines, namely SCLK, I/O, and RST; the data is written to the DS1302 on the rising edge of the next SCLK clock after the control instruction word is input, and the data input starts from the low bit, i.e., bit 0. Similarly, the data of the DS1302 is read out on the falling edge of the next SCLK pulse following the 8-bit control instruction word [2]. 2.2.3 The DS18B20 temperature measurement module [3] is the latest single-wire digital temperature sensor from DALLAS, which can directly convert the temperature signal into a serial digital signal for microcomputer processing; in this system, the resolution of the DS18B20 is set to 12 bits; therefore, the actual temperature = the integer part of the temperature + the fractional part of the temperature * 0.0625. 2.2.4 The humidity measuring module HS1101 is equivalent to a capacitor in the circuit. Its capacitance increases with the relative humidity of the measured air. It has excellent linear output. In the range of relative humidity (0-100)%RH, its error is no greater than ±2%RH. The annual drift is 0.5%RH/year, and the response time is less than 5S[4]. The humidity-sensitive capacitor is placed in the 555 oscillator circuit, and the change in capacitance value is converted into a voltage frequency signal that is inversely proportional to it, which can be directly collected by the computer[5]. 2.2.5 The LED display module is composed of 10 LED digital switches driven by one SN74LS145N chip to synchronously display the temperature value, humidity value and current time. 2.2.6 External storage module The external storage module adopts the 24C512 chip with a capacity of 64K bytes from ATMEL. It uses the I2C bus for read and write operations and can store 6520 historical data records. 2.2.7 The address module consists of an 8-bit DIP switch module, which uses the 8421 encoding method to determine the address of each temperature and humidity meter. 2.3 The RS485 to TCP/IP protocol converter of the unit temperature and humidity monitoring system is mainly responsible for the mutual conversion and transmission between serial port data frames and Ethernet data frames. After the processor receives the Ethernet data packet, it first queues the data packet according to a certain queuing rule. The data is placed in the buffer in a certain order. When a certain limit is reached, the internal data processing chip starts to process the data frame and then sends it out in the form of serial port data frame. Conversely, when serial port data arrives, the converter converts the serial port data frame into an Ethernet data frame. The processing process is similar, and the two processing processes are the inverse of each other [6]. 3 Working principle of temperature and humidity monitor Power-on initialization, read and save the temperature and humidity meter address according to the state of the DIP switch on the board; read the historical values ​​of the previously set upper and lower limits of temperature and humidity and the historical values ​​of the saved sampling interval stored in the external memory. Then, in the main loop, according to the sampling interval time, the temperature, humidity and other data are stored in the external storage, the LED digital tube is lit to display the current time, temperature and humidity, and the buzzer alarm is driven and the air conditioner, humidifier and dehumidifier are controlled to work to adjust the temperature and humidity according to the set upper and lower limits of temperature and humidity [7] (see Figure 3 for the schematic diagram of upper and lower limit control of temperature and humidity). The system has good interactive performance. The time correction value, upper and lower limits of temperature and humidity, sampling interval time value and temperature and humidity correction value can be set online at any time using interrupts and these data can be stored in the external storage; the current temperature and humidity data and the status of the temperature and humidity meter can be extracted online; the historical temperature and humidity data already stored in the external storage can be extracted by the corresponding instructions according to the sampling interval. [align=center] Figure 3 Schematic diagram of temperature and humidity upper and lower limit control[/align] The instruction format sent by the microcomputer is: FF + slave address + instruction code + data. The temperature and humidity controller can receive the instruction according to whether the broadcast slave address matches its own address in the interrupt program, and perform corresponding actions according to the instruction to set the time correction value, temperature and humidity upper and lower limit values, sampling interval time value, temperature and humidity correction value, and store these data in external storage to prevent loss in case of power failure. 4 PC software design The software part of this temperature and humidity monitoring system includes the following five functional modules: I. System settings: (1) Setting temperature and humidity upper and lower limits, date, sampling interval, interface converter parameters, etc.; (2) User password modification, system user information management; (3) Warehouse unit management, temperature and humidity instrument management. II. Data extraction: (1) System users can extract historical temperature and humidity data at any time and store them in the system database; (2) System users can extract current temperature and humidity data and current temperature and humidity working status at any time. II. Data acquisition and analysis: (1) Acquisition of temperature and humidity data; (2) Analysis of current data. IV. Data Query and Analysis: The system allows querying of existing data by year, month, and day, and analysis of the results, displaying the results in tables or graphs. V. Data Backup and Recovery: The system performs backup and recovery operations on historical data in the database. 5. Conclusion This system is highly flexible and interactive, allowing users to set temperature and humidity limits, sampling intervals, correction values, and other parameters online as needed. The system design and development fully utilizes the concept of hardware and software co-design, with modular design in each part. It can be easily modified to become a multi-warehouse distributed remote intelligent temperature and humidity monitoring system suitable for various scenarios. The system is already in operation, stable, reliable, and has strong real-time performance. It fully utilizes existing networks, facilitating the rapid transformation of traditional RS485-based temperature and humidity monitoring systems into large-scale distributed remote intelligent temperature and humidity monitoring systems, achieving significant social and economic benefits. References: [1] Zhang Weimin. Development of intelligent controller in temperature and humidity measurement and control system [J] Journal of Northwest University for Nationalities (Natural Science Edition) 2004, 25 (53): 42-46. [2] Wang Changlong, Wang Zizhang, He Fuyou et al. Serial clock chip DS1302 and its application in sprinkler controller [J] Microcomputer Information, 2000, 16 (6): 62-63. [3] Liang Jibao, Shan Dongsheng, Zhu Bin. 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