In the early 1990s, an electronic patrol product was produced in the United States, which was followed by people in China. It used touch buttons to automatically record time and card numbers and was a contact electronic patrol product. In the late 1990s, with the maturation of radio frequency identification technology (RFID), non-contact, inductive patrol products emerged and gradually occupied the market. Since 2001, the electronic patrol system consists of an inspection device, an information button, and a computer management system. In this mode, its products have been continuously improved. The technology is widely used in coal mines, education,*, grain storage, railways, telecommunications, factories, and residential communities, resulting in a new technology.
1 Electronic patrol system based on RFID technology
The electronic patrol system has only been developing for more than 10 years, and it has formed a fixed model, namely offline, non-contact patrol system, and has become the mainstream product in the market. Designers are limited by the technology, leaving out the advantages of real-time monitoring that the online non-contact patrol system has, even though it eliminates the way touch buttons read information and replace it with non-contact radio frequency identification (RFID) technology. Sensing to read information, but the maximum recognizable distance is only within 13cm, which brings great inconvenience to the normal work of inspection personnel. This article is based on RFID technology designed patrol system, and use nRF2401 wireless transceiver chip to establish the system, can better both have the advantages. The system's operating frequency is 2.4GHz and the identification distance can reach 5-20in.
2 system composition
The system consists of inspection probes, inspection cards, inspection controllers, and computer system management systems.
(1) Inspection probe. The inspection point consists of an inspection probe. The inspection probe can receive the data code sent by the inspection card and send it to the next inspection probe. The communication network is composed of wireless communication between every two probes, and the information data is finally sent to the inspection. Controller. The inspection probe is actually an independent wireless contact, and the communication distance between the two probes is limited by the wireless transmission distance. In order to ensure the reliability of the communication data, it is actually less than the maximum transmission distance. The point-to-point communication method is adopted between each inspection probe, and a communication protocol is written by software to realize relay transmission. The patrol probe is an active device that requires power supply. If a regulated power supply is used, a 220V power supply is required. Dry batteries or rechargeable batteries may also be used to provide power. Installation is convenient.
(2) inspection card. The inspection card is a kind of active card carried by inspectors and can also be made into a key chain and hung on the waist. Built-in 3V button battery, because it is active launch, the role of distance is greatly enhanced, usually can be set in the range of 5-10In distance, no directional requirements. It can be carried on the body or inside the bag without removing it.
(3) inspection controller. The inspection controller receives the data sent by each inspection probe through the master-slave wireless communication method. This is composed of the inspection personnel code, the inspection probe code and the current time, and the data is stored in the flash memory (FLASHMEMORY). Inside, communicate with the computer through the RS232 interface. The inspection controller, the inspection probe and the inspection card are self-contained systems, which do not need to be connected or communicated with the microcomputer at ordinary times, and are only operated by software when communication and real-time monitoring are required.
(4) Microcomputer management system. The data stored in the flash memory (FLASH MEMORY) of the inspection controller is transmitted through the RS232 interface, and is stored in the file system as a database. According to the frequency and time interval of the patrol, each record can be compared item by item to confirm whether it is valid. The results of each record can be queried in multiple ways, statistics can be made and various reports used by managers can be made, and the conditions of each inspection probe can also be monitored in real time as required.
3 Chip Configuration and ShockBurstM Transceiver Mode
Before the wireless communication, no matter whether the chip is transmitting or receiving, it needs to be configured first after power-on. The configuration word of l4J4 bit specifies the receiving address, transceiver frequency, transmit power, wireless transmission rate, wireless transceiver mode, and CRC check length. And effective data length. When the nRF2401 is set in ShockBurst. When the M transceiver mode is in operation, there is a feature that a low-speed MCU can be used to transmit data, temporarily stored in the on-chip first-in-first-out stack (FIFO), and then transmitted to the air at a high-speed (1 Mbps) rate. The use of ShockBurst technology has three major advantages: it reduces the average operating current of the system (only when the launch, the short-time current is larger); short-time high-speed transmission, the data in the air for a short residence time, high anti-interference; low system costs ( Low-speed microprocessors can also perform high-speed RF emissions.
4 wireless network structure
Each patrol probe forms a wireless communication network with each other through radio waves. The system uses a wireless mesh network, that is, point-to-point communication. Since each contact has a microprocessor, wireless communication between one point and another point is not required without a wireless router. Each wireless contact can not only send and receive data, but also can forward data to adjacent wireless contacts. There are multiple wireless contacts. The mutual connection can make the transmission distance farther. When a contact in a wireless network fails, adjacent contacts automatically replace the failed contact, keeping the network communication normal.
5 hardware components
The connection between the MCU and the NRF2401DE1 is shown in Figure 7. The single-chip microcomputer adopts AT89CL51, and the wireless transceiver chip selects nRF2401 chip. These two kinds of chips all work at a low voltage of +3V. Microcontroller software is written in KEILC51 or assembly language. ShockBurstTM transceiver mode can be set before data transmission and reception. Theoretically, 100nl can be transmitted, which can reach 20-50nl in the experiment, depending on the high-frequency performance of the device used in the circuit, the arrangement of components, and the grounding of the circuit board.
6 inspection process
As shown in Figure 1, when the patrolman is carrying the card on the specified tour route. At this point, the inspection probe receives the identification code sent by the inspection card, sends it to the next probe for relay transmission, and sends a signal to the inspection card at the same time, so that the receiving and sending circuits of the card are in a dormant state (power saving). When the inspector arrives at point b, the inspection probe mouth may not receive a signal (the inspector card is still in a dormant state), or may receive a signal, and will not do any work after the judgment, (taken the first time The data arrived shall prevail. When the inspector arrives at point c, the inspection probes 0 and b may receive signals, but the inspection probe should judge that the probe b is working and inspect the probe. Still based on the data received for the first time, the data received and transmitted by each inspection probe is finally transmitted to the inspection controller and stored in the flash memory.
7 inspection probe software process
8 Communication Protocol
Wireless communication is different from wired communication, and the probability of wireless communication errors is higher than that of wired communication systems. Wireless communication uses a common propagation medium, which determines that wireless communication must design a large number of wireless communication protocols to solve the problem of reliably sending and receiving data in the same propagation medium and preventing collision of data packets in the air. Using the nRF2401 wireless transceiver chip, you only need to design point-to-point, point-to-multipoint, multi-node processing communication protocols.
(1) The peer-to-peer communication method is adopted between the inspection card and the inspection probe. The inspection probe and the inspection controller also adopt a peer-to-peer communication method, and a point-to-multipoint communication method is adopted between the inspection probes.
(2) The RS232 serial communication mode is used for data exchange between the PC and the inspection controller.
(3) When the nRF2401 wireless transceiver chip works in the ShockBurstIII transceiver mode, it automatically processes the header and the CRC to ensure the accuracy of the transmitted and received data. When receiving data, the header and CRC are automatically removed. When sending data, prefixes and CRC checksums are automatically added. After the transmission is completed, the data is ready for the pin to notify the microprocessor that the data has been transmitted.
9 Conclusion
The hardware verification experiment was first performed on the system, and then the software design experiment was performed. The desired result was achieved.
VB6.0 serial communication programming, database management system using Delphi5.0 to design a visual graphical interface, database access and real-time monitoring interface. In the database, it is necessary to design the basic data sheet, duty schedule sheet, and work record sheet of the patrol personnel. The system is based on RFID technology, the use of wireless channels for data transmission, the current widely used mobile phone technology is also the use of wireless channels for data transmission, its easy to use, flexible and well-known. The wireless communication channel is the worst one of all communication media, and the transmission characteristics are not as mature as using RS485 and CAN bus. It is undoubted that the wireless communication channel is undoubtedly highly competitive in places where the conditions are not particularly strict. Easy to install, easy to expand, is an ideal communication solution.
Wireless communication operating at 2.4 GHz places high demands on designers' hardware and software design. In high frequency environments, design experience becomes very important. Wireless communication channel In the current trial patrol system, the utilization rate is very low, most of them are idle, and the diversified development of the inspection system is an inevitable trend. Wireless voice, camera, and image processing functions will be applied to Inspect the system. The patrol probe is bound to develop into a "smart" probe, plus a computer network function to form a new generation of electronic patrol inspection system.
1 Electronic patrol system based on RFID technology
The electronic patrol system has only been developing for more than 10 years, and it has formed a fixed model, namely offline, non-contact patrol system, and has become the mainstream product in the market. Designers are limited by the technology, leaving out the advantages of real-time monitoring that the online non-contact patrol system has, even though it eliminates the way touch buttons read information and replace it with non-contact radio frequency identification (RFID) technology. Sensing to read information, but the maximum recognizable distance is only within 13cm, which brings great inconvenience to the normal work of inspection personnel. This article is based on RFID technology designed patrol system, and use nRF2401 wireless transceiver chip to establish the system, can better both have the advantages. The system's operating frequency is 2.4GHz and the identification distance can reach 5-20in.
2 system composition
The system consists of inspection probes, inspection cards, inspection controllers, and computer system management systems.
(1) Inspection probe. The inspection point consists of an inspection probe. The inspection probe can receive the data code sent by the inspection card and send it to the next inspection probe. The communication network is composed of wireless communication between every two probes, and the information data is finally sent to the inspection. Controller. The inspection probe is actually an independent wireless contact, and the communication distance between the two probes is limited by the wireless transmission distance. In order to ensure the reliability of the communication data, it is actually less than the maximum transmission distance. The point-to-point communication method is adopted between each inspection probe, and a communication protocol is written by software to realize relay transmission. The patrol probe is an active device that requires power supply. If a regulated power supply is used, a 220V power supply is required. Dry batteries or rechargeable batteries may also be used to provide power. Installation is convenient.
(2) inspection card. The inspection card is a kind of active card carried by inspectors and can also be made into a key chain and hung on the waist. Built-in 3V button battery, because it is active launch, the role of distance is greatly enhanced, usually can be set in the range of 5-10In distance, no directional requirements. It can be carried on the body or inside the bag without removing it.
(3) inspection controller. The inspection controller receives the data sent by each inspection probe through the master-slave wireless communication method. This is composed of the inspection personnel code, the inspection probe code and the current time, and the data is stored in the flash memory (FLASHMEMORY). Inside, communicate with the computer through the RS232 interface. The inspection controller, the inspection probe and the inspection card are self-contained systems, which do not need to be connected or communicated with the microcomputer at ordinary times, and are only operated by software when communication and real-time monitoring are required.
(4) Microcomputer management system. The data stored in the flash memory (FLASH MEMORY) of the inspection controller is transmitted through the RS232 interface, and is stored in the file system as a database. According to the frequency and time interval of the patrol, each record can be compared item by item to confirm whether it is valid. The results of each record can be queried in multiple ways, statistics can be made and various reports used by managers can be made, and the conditions of each inspection probe can also be monitored in real time as required.
3 Chip Configuration and ShockBurstM Transceiver Mode
Before the wireless communication, no matter whether the chip is transmitting or receiving, it needs to be configured first after power-on. The configuration word of l4J4 bit specifies the receiving address, transceiver frequency, transmit power, wireless transmission rate, wireless transceiver mode, and CRC check length. And effective data length. When the nRF2401 is set in ShockBurst. When the M transceiver mode is in operation, there is a feature that a low-speed MCU can be used to transmit data, temporarily stored in the on-chip first-in-first-out stack (FIFO), and then transmitted to the air at a high-speed (1 Mbps) rate. The use of ShockBurst technology has three major advantages: it reduces the average operating current of the system (only when the launch, the short-time current is larger); short-time high-speed transmission, the data in the air for a short residence time, high anti-interference; low system costs ( Low-speed microprocessors can also perform high-speed RF emissions.
4 wireless network structure
Each patrol probe forms a wireless communication network with each other through radio waves. The system uses a wireless mesh network, that is, point-to-point communication. Since each contact has a microprocessor, wireless communication between one point and another point is not required without a wireless router. Each wireless contact can not only send and receive data, but also can forward data to adjacent wireless contacts. There are multiple wireless contacts. The mutual connection can make the transmission distance farther. When a contact in a wireless network fails, adjacent contacts automatically replace the failed contact, keeping the network communication normal.
5 hardware components
The connection between the MCU and the NRF2401DE1 is shown in Figure 7. The single-chip microcomputer adopts AT89CL51, and the wireless transceiver chip selects nRF2401 chip. These two kinds of chips all work at a low voltage of +3V. Microcontroller software is written in KEILC51 or assembly language. ShockBurstTM transceiver mode can be set before data transmission and reception. Theoretically, 100nl can be transmitted, which can reach 20-50nl in the experiment, depending on the high-frequency performance of the device used in the circuit, the arrangement of components, and the grounding of the circuit board.
6 inspection process
As shown in Figure 1, when the patrolman is carrying the card on the specified tour route. At this point, the inspection probe receives the identification code sent by the inspection card, sends it to the next probe for relay transmission, and sends a signal to the inspection card at the same time, so that the receiving and sending circuits of the card are in a dormant state (power saving). When the inspector arrives at point b, the inspection probe mouth may not receive a signal (the inspector card is still in a dormant state), or may receive a signal, and will not do any work after the judgment, (taken the first time The data arrived shall prevail. When the inspector arrives at point c, the inspection probes 0 and b may receive signals, but the inspection probe should judge that the probe b is working and inspect the probe. Still based on the data received for the first time, the data received and transmitted by each inspection probe is finally transmitted to the inspection controller and stored in the flash memory.
7 inspection probe software process
8 Communication Protocol
Wireless communication is different from wired communication, and the probability of wireless communication errors is higher than that of wired communication systems. Wireless communication uses a common propagation medium, which determines that wireless communication must design a large number of wireless communication protocols to solve the problem of reliably sending and receiving data in the same propagation medium and preventing collision of data packets in the air. Using the nRF2401 wireless transceiver chip, you only need to design point-to-point, point-to-multipoint, multi-node processing communication protocols.
(1) The peer-to-peer communication method is adopted between the inspection card and the inspection probe. The inspection probe and the inspection controller also adopt a peer-to-peer communication method, and a point-to-multipoint communication method is adopted between the inspection probes.
(2) The RS232 serial communication mode is used for data exchange between the PC and the inspection controller.
(3) When the nRF2401 wireless transceiver chip works in the ShockBurstIII transceiver mode, it automatically processes the header and the CRC to ensure the accuracy of the transmitted and received data. When receiving data, the header and CRC are automatically removed. When sending data, prefixes and CRC checksums are automatically added. After the transmission is completed, the data is ready for the pin to notify the microprocessor that the data has been transmitted.
9 Conclusion
The hardware verification experiment was first performed on the system, and then the software design experiment was performed. The desired result was achieved.
VB6.0 serial communication programming, database management system using Delphi5.0 to design a visual graphical interface, database access and real-time monitoring interface. In the database, it is necessary to design the basic data sheet, duty schedule sheet, and work record sheet of the patrol personnel. The system is based on RFID technology, the use of wireless channels for data transmission, the current widely used mobile phone technology is also the use of wireless channels for data transmission, its easy to use, flexible and well-known. The wireless communication channel is the worst one of all communication media, and the transmission characteristics are not as mature as using RS485 and CAN bus. It is undoubted that the wireless communication channel is undoubtedly highly competitive in places where the conditions are not particularly strict. Easy to install, easy to expand, is an ideal communication solution.
Wireless communication operating at 2.4 GHz places high demands on designers' hardware and software design. In high frequency environments, design experience becomes very important. Wireless communication channel In the current trial patrol system, the utilization rate is very low, most of them are idle, and the diversified development of the inspection system is an inevitable trend. Wireless voice, camera, and image processing functions will be applied to Inspect the system. The patrol probe is bound to develop into a "smart" probe, plus a computer network function to form a new generation of electronic patrol inspection system.
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Specification
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