Software and hardware design of remote meter reading system based on AT89C51 and serial Internet interface equipment

With the improvement of living standards, people's consumption of resources is increasing day by day, and the measurement, management and charging of resource consumption are becoming increasingly complicated. Products that improve the management level and automation level have emerged as the times require. However, in the past, the reading of energy consumption meters was manual, which could not guarantee the accuracy and real-time nature of the data. It would also cause a lot of waste of manpower, material resources and time, and also lead to the phenomenon of wrong reading, missing reading and estimated reading. Therefore, traditional over-standard methods are increasingly unable to adapt to future residential development needs and people's living needs. They will be replaced by outdoor remote meter reading systems, which use sensing, control, network and other technologies to measure the energy consumption of each user. The table data is automatically collected into the collector, and then the collector transmits the data to the outdoor centralized controller, and then transmits the data to the upper monitoring host through the network for analysis, measurement and storage. Finally, the energy supply company charges electronically based on the household consumption costs calculated by the host computer. This method not only saves manpower, material resources, and time, but also ensures accuracy and real-time performance.

System composition and working principle

The remote meter reading system is mainly composed of three parts: PC host computer, centralized controller and collector. The structural block diagram of the system is shown in Figure 1.

Figure 1 General framework diagram of the system

As can be seen from the above figure, the meter reading system is divided into three levels. The top layer is the community central processor, which is used for comprehensive monitoring; the middle layer is composed of the community's internal LAN (Ethernet), which is a large channel for data transmission; the bottom layer It is the four-meter data collection layer, which is composed of RS485 network and completes the function of collecting, concentrating and transmitting the data of the four meters to the host computer. The upper layer is a software system with a friendly interface and easy operation designed using VB language. Users only need simple key operations to realize remote sending and receiving of data through the network port. The command sent is sent to the remote network port to serial port device via the internal LAN. The middle-level central controller is mainly responsible for identifying commands and implementing related operations of the commands, such as full meter reading, single-user meter reading and scheduled meter reading commands. The issued commands are transmitted to the collectors in each user's home via the RS485 bus network, and then the pulse meters (such as gas meters, water meters, electricity meters, etc.) are read and stored, and finally uploaded via the RS485 bus.

System main hardware circuit design

The advantage of this system is that it can transmit the four-meter data through the local area network in the community. It uses the serial Internet interface device NportExpressDE-311 of Taiwan Momo Company. It is a single-chip network access device with two ports, one is an RS232 or RS485 level input interface, and the other is a network interface. It automatically communicates internally. The data is encapsulated by TCP/IP and is completely transparent to the user, as shown in Figure 2. This device has become very popular on the market.

Figure 2 Nport application diagram

The hardware circuit design of the controller mainly includes CPU, peripheral storage module and data upload/download module. Its structure is shown in Figure 3. In this design, the CPU is AT89C51; the peripheral memory module is the serial E2PROM 24C02 chip, which is a storage device based on I2C-BUS and follows the two-wire protocol. It has convenient interfaces, small size, and non-volatile data when power is lost. Features, widely used in instrumentation and industrial automation control. The system design adopts the principle of pulse meter reading. The four meters are all pulse-type digital meters, mainly composed of Hall sensors. The sensor in the digital meter emits a pulse every time it rotates once, making the consumption proportional to the number of pulses. The specific value of the dosage can be determined based on the number of pulses. The acquisition module is mainly composed of four chips, including ULN2003, 74LS378, 7411, and CD40174. It can collect up to 6 channels of data. Since only four tables of data are collected in this design, two channels are left unused.

Figure 3 Hardware circuit of the controller

Q0~Q3 of CD40174 chip are connected to P1.0~P1.3 of AT89C51 respectively. At the same time, the negative pulse signal generated by the 7411 chip is sent to INT0 of the microcontroller, so that when an intelligent terminal pulse is generated, the CPU can generate an interrupt for collection. By cyclically querying P1.0~P1.3, you can know which digital table the collected pulse numbers come from. The acquisition program flow is shown in Figure 4.

Figure 4 Collection program flow chart

System software system design

The software design of the system mainly includes two parts, one is the C language programming of the collector and central controller, and the other is the control program programming of the host computer. Here we mainly introduce the host computer program programming. The upper computer operating platform adopts VB programming, and the connection with the network is completed through a universal control Winsock. The Winsock control is invisible to users. It provides a convenient way to access TCP and UDP network services. You can easily connect to a remote machine by setting the properties of the control and calling it, and you can also exchange data in both directions. It provides two transmission modes, TCP and UDP. Since TCP mode is a connection-oriented transmission method, before transmitting data, both communicating parties must receive the response signal from the other party to start the data transmission. Therefore, it takes up a lot of time to complete the transmission of handshake signals, while UDP mode It is a communication method for fast access to data. There is no need to re-establish the connection between sending and receiving, saving connection time. UDP mode is used in this design. The software system design chose to use Vista transparent form style, which mainly includes software login module, user management module, system setting module, meter reading setting module, data management module, billing setting module, etc., most of which are involved in the module design. Come to the database operation.

Conclusion

This system overcomes the shortcomings of the traditional wired meter reading method and transmits large amounts of data, high accuracy, and low communication costs. Based on Proteus technology, it has flexible networking and easy expansion, which reduces the difficulty and cost of design and construction. It has good openness, reliability and scalability, and has important practical significance and broad development prospects.