Introduction Does your family encounter the following problems: rust, sediment, or other substances in your tap water? Stubborn scale builds up after boiling? An unpleasant odor in your tap water? Is your once clear tap water becoming increasingly turbid? With rapid economic development, environmental pollution is becoming increasingly serious, especially in drinking water. Water contains various components, such as sulfur and sulfuric acid. Timely monitoring is crucial for environmental protection. Currently, China's tap water testing methods still rely on manual sampling and experimental analysis. This method has a low frequency, cannot accurately reflect the actual water quality, and is not easily integrated into a unified monitoring network. While network communication is rapidly developing and networking technologies are becoming more diverse and mature, considering the characteristics of a large number of monitoring points, small data transmission volume, and high cost-effectiveness requirements, we have developed an automatic tap water composition monitoring system based on a telephone network. 1. System Composition and Functions This system mainly consists of three parts: on-site monitoring, a communication network (telephone network), and a central monitoring and control unit. Figure 1 below shows the overall system structure. Figure 1 shows the system structure. The field monitoring module is placed at various locations requiring monitoring. It consists of various sensors and a microprocessor, used to collect various water parameters such as color, pH value, turbidity, total hardness, and sulfur content. The collected data are processed by the microprocessor and stored in corresponding storage units. Data is transmitted to the central control unit via the telephone network on a timed basis, or as directed by the central control unit. Communication between the field monitoring module and the central control unit is achieved through the existing telephone network. Data is transmitted in DTMF signal mode. Most current keypad telephones use DTMF dialing. DTMF selection uses eight frequency bands, including four low-frequency bands (679Hz, 770Hz, 852Hz, 941Hz) and four high-frequency bands (1209Hz, 1336Hz, 1477Hz, 1633Hz). Each key corresponds to the sum of a low-frequency and a high-frequency sine wave. The main functions of the central monitoring and control unit are: First, to manage information from various locations and the types of sensors. Second, to set parameters for the field monitoring modules, such as the sensor sampling frequency and data upload method. Third, to perform analysis, storage, display, report generation, printing, and output functions for the data uploaded by the field monitoring modules. 2. Hardware and Software Implementation of the System 2.1 Hardware Implementation of the Field Monitoring Module The main components of the field monitoring module are a multi-channel sensor, a DTMF signal transceiver, and a microprocessor based on the 89S51 microcontroller, as shown in Figure 2. Figure 2 Hardware Schematic Diagram of the Field Monitoring Module The multi-channel sensor collects water indicators. The sensor type is represented by codes 01, 02, and 03, such as 01 representing color, 02 representing pH value, and 03 representing total hardness. Different sensor types can be used to adapt to different regions. The voltage signal collected by the sensor is processed by a signal conditioning circuit, a multiplexer, and converted into a digital signal by an A/D converter. It is then processed by the CPU and stored in the AT45DB011 memory. The AT45DB011 is a serial FLASH memory manufactured by Atmel, with 1MB of storage space. The data collected by the sensors is stored in partitions for easy CPU access. The microprocessor selected is the AT89C51. It is a low-power, high-performance processing chip manufactured by Atmel, with 4K of on-chip memory and a wide operating frequency range. 2.2 Hardware Implementation of the Central Measurement and Control Unit The central measurement and control unit consists of a DTMF transceiver, the AT89C51, and a host computer, as shown in Figure 3: Figure 3 Hardware Schematic Diagram of the Central Measurement and Control Unit The AT89C51 communicates with the host computer via an RS-232 interface. Its main task is to receive and analyze the data uploaded by the field monitoring module and display it in a visual interface, and to set the sensor parameters. 2.3 Transmission and Hardware/Software Implementation of DTMF Signals The MT8880 manufactured by Atmel can realize DTMF data transmission and reception, and signal tone judgment. It has the following basic functions: 1. Provides complete DTMF transmission or reception functions. 2. Has the function of receiving signal tones and bandpass filtering. 3. Can directly interface with the microprocessor. The CPU uses the AT89C51 chip, which can control the sending, receiving, and operating modes of the MT8880. The format of data sent from the field detection module to the host computer in DTMF format is shown in Table 1. For example, "#05101809080212*" represents: at 9:08 AM on October 18, 2005, sensor 02 collected data showing a rainfall of 12 mm in a certain area. The format of control commands sent from the central control unit to the field monitoring module in DTMF format is shown in Table 2. Different command codes represent different control commands sent from the host computer to the field monitoring module, and different control commands have different command value formats. MT8880 sends subroutine: SEND: MOV DPTR, #2100H SETB P1.0 MOV A, #0CH MOVX @DPTR,A MOV A, #00H MOVX A, R0 MOV DPTR, #2000H MOVX @DPTR,A CLR P1.0 S1: MOV DPTR, #2100H MOVX A, @DPTR JB ACC.1,W_1 RET RECEIVE:MOV DPTR,#2100H SETB P1.0 MOV A,#0CH MOVX @DPTR,A MOV A,#00H MOVX @DPTR,A MOVX DPTR,#2100H CLR P1.0 R_1: MOVX A,&# 64;DPTR JNB ACC.2,R_1 SETB P1.0 MOV DPTR,#2000H MOVX A,@DPTR ANL A,#0CH MOV R0,A RET 3 Summary Through the above scheme, using the telephone network, real-time online monitoring of water components in various locations can be achieved. This system features convenient networking, security, and high cost-effectiveness. It enables environmental workers to understand the water situation in various locations in a timely and accurate manner, realizing remote monitoring. [b]References:[/b] 1. Li Chaoqing. Single-chip microcomputer principle and interface technology. Beijing: Beijing University of Aeronautics and Astronautics Press, 2002 2. Wan Fujun. Single-chip microcomputer principle system design and application. Beijing: University of Science and Technology of China Press, 2003 3. Fu Jiacai. Single-chip microcomputer control engineering practice technology. Beijing: Chemical Industry Press, 2004 4. Zhang Zhengwei. Sensor principle and application. Beijing: Central Radio and Television University Press, 2001 Editor: He Shiping