Abstract: With the rapid development of science and technology, traditional water meter technology is no longer suitable for today's property management needs. Compared with wireless automatic water meter technology, wireless automatic water meter technology has the advantages of not entering the household, low management cost, fast and avoiding mis-copying and mis-copying. . Based on this, a wireless meter reading system is designed. The design consists of two parts: the remote user terminal module and the wireless transceiver module. These two parts are composed of the RF chip CC2480 and the corresponding circuit, and adopt the latest Z-Z1 launched by T1. Aeee1 series processor. Read the water meter data by binary counting method. This data is then collected through the RF section. Realize multi-user data collection without going to the home, and the cost is lower.
Keywords: Zigbee; wireless network; IEEE 802.15.4 specification; CC2480; traditional water meter; wireless water meter
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0 Introduction With the rapid development of modern technology, wireless meter reading systems are increasingly favored by people and gradually replace the traditional meter reading system. Traditional meter reading systems can be roughly divided into three categories: smart card water meters, wired automatic meter reading systems. , wireless smart water meter. Among them, the wired automatic meter reading system can be divided into a centralized line meter reading system and a bus system centralized meter reading table. Due to the disadvantages of the first two methods, wireless automatic meter reading systems are attracting more and more attention from the industry.
l Zigbee technology introduction
1.1 Zigbee Technology Overview Zigbee adopts the IEEE 802.15.4 communication standard and works in the 2.4 GHz band free of application and free use. It is an emerging short-range, low-power, low data rate, low-cost, Low-complexity wireless network technology, mainly used for short-distance transmission, suitable for wireless data acquisition, wireless industrial control, consumer electronics, automotive automation, home and building automation, medical equipment control, remote network control and other occasions. Zigbee technology has the following advantages over Bluetooth and Wi-Fi:
Low data transfer rate: 10 to 250 KB/s, focusing on low transmission applications.
Low power consumption: In the low-power standby mode, two ordinary 5th batteries can be used for 6 to 24 months.
Low cost: Zigbee has a low data transfer rate and a simple protocol, which greatly reduces the cost.
Large network capacity: The network can hold 65,000 devices.
The delay is short: the typical search device delay is 30 ms; the sleep activation delay is 15 ms; the active device channel access delay is 15 ms.
The network has self-organization, self-healing ability and reliable communication.
Data Security: Zigbee provides data integrity checking and authentication capabilities. The AES-128 encryption algorithm allows each application to flexibly determine its security attributes.
1.2 Zigbee network topology Zigbee technology has powerful networking capabilities, which can form a star, tree and MESH mesh network as shown in Figure 1. In practice, choose the appropriate network structure as needed.
The network coordinator is the central node in the network, the organizer of the network, responsible for network formation and information routing; the full-featured device FFD can be used as a coordinator, is a network node with routing and relay functions, and can communicate with the RFD node. It can also communicate with other FFD nodes; the reduced functional device RFD nodes act as network terminal nodes, which cannot communicate directly with each other, can only send and receive information through the FFD node, and have no routing and relay functions. But the hardware structure of FRD and FFD is exactly the same, but the network layer is different.
2 Design scheme This design is mainly used for automatic meter reading of building water meters, and meter reading personnel can read back the table data without entering each household. Figure 2 is a block diagram of the Zig-bee communication in the unit building. The overall design is to first install a Zigbee data acquisition module in the unit building, which is convenient for the meter reader to collect the data of each household water meter; at the same time, a Zigbee remote user terminal module is installed in each household, which is mainly used for reading the water meter. The data is then transmitted to Zigbee's data acquisition module via the Zigbee's RF section.
2.1 CC2480 introduces Zigbee remote user terminal module and Zigbee data acquisition module. Zigbee part adopts Texas Instruments (TI) to announce the first product in the latest Z-Accel series 2.4 GHz Zigbee certified network processor - CC2480 To complete, the CC2480 requires very few peripherals (the peripheral circuitry is shown in Figure 3) and the device does not need to understand the cumbersome full-featured Zigbee protocol stack, which reduces development time and simplifies Zigbee functionality. The CC2480 can communicate with a variety of MCUs via SPI or UART interfaces, as well as with TI's MPS430 ultra-low-power MCUs. The Z-stack software Zigbee-2006 protocol stack can run on Zigbee processors, while applications can run on external MCUs. The CC2480 is capable of handling all timing-critical and processing-intensive Zigbee protocol tasks, freeing up the space occupied by the application MCU's resources to meet the requirements of other programs. Figure 2 Zigbee communication block diagram in the unit building
2.2 Zigbee Remote User Terminal Module The Zibbee Remote User Terminal Module is installed in each household in the unit building. The data line is read by using 8 data lines in the remote user terminal module, and the connection between the 8 data lines and the water meter is not discussed here. The Zigbee remote user terminal module is shown in Figure 4. Among them, the data lines 1, 2, 3 are used to control a certain position of the water meter data through three-line decoding; the data lines 4, 5, 6, 7 are used to display data on a certain position of the water meter; 8 is a ground line. For example, if the data lines 1, 2, and 3 are in the state of 000, the 4, 5, 6, and 7 digits display the first digit reading of the water meter; the data lines 1, 2, and 3 are 111, and 4, 5, 6, The 7-digit display number is the eighth digit reading of the water meter. After each reading, it is sent to the Zigbee module for processing.
2.3 Zigbee data acquisition module Zigbee data acquisition module (see Figure 5) is installed in a layer in the unit building or more convenient for the reader to read the table. When the Zigbee module receives the data, it outputs the data to the LED display through the LED driver chip, so that the reading staff can clearly read the reading, wherein the first two digits are used to display the room number of each household, and the last six digits are used to display the corresponding room number. Water meter data. The keyboard is used to control the LED display. Among them, the smart keyboard and LED driver and USB driver use chip RIC16C63 and chip USBN9602 respectively.
The RIC16C63 is a high performance 8-bit microprocessor with a superior RISC architecture and a command system with only 35 instructions. With UARST, SPI, I2C multiple serial drive functions, there are three timers on the chip. Its characteristics are as follows:
(1) The I2C interface is used for the link mode with the CPU (the USART serial communication interface method or the three-wire SPI interface method can also be used).
(2) Up to 16 keyboard inputs provide keyboard interrupt signal.
(3) 8 LED digital tubes can be provided, BCD code digital drive mode or segment drive mode can be selected, and LED brightness software setting function is available.
(4) Simultaneously perform keyboard and display operations.
The USBN9602 is a standard dual in-line 28-pin chip. The chip has a total of 7 transmit/receive FIFO buffers, 1 bidirectional transmit and receive FIFO buffer, 3 unidirectional transmit FIFO buffers, and 3 unidirectional receive FIFO buffers. USBN9602 is widely used in measurement and control technology, data acquisition, signal processing and so on.
3 Conclusion The wireless automatic water meter system supported by Zigbee network technology greatly reduces the running cost and power consumption compared with manual meter reading or other automatic water meter system, and the work efficiency is obviously improved. The node hardware is also easy to implement, avoiding the cable. Various problems caused by the construction and wiring of the meter reading system. The solution proposed by the design, the hardware has been realized, when the user uses the water wheel of the user water meter to scroll, the Zigbee remote terminal user module collects the water meter data through the decoding method, and then transmits the data to the Zigbee data acquisition module through the RF part of the module. The collected data sometimes has a delay, which may be caused by the RF part of Zigbee. Therefore, a lot of experiments are needed to adjust the RF part of Zigbee to make the collected data more accurate.
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