Design of RFID Extensible AMR Parking Space Detection System Based on WiFi
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introduction
Real-time detection of parking spaces in parking lots is the key to realize the intelligent management of parking lots and improve the utilization rate of parking spaces. It is also a requirement for modern parking management. The development of the parking space detection system in the parking lot has generally experienced three stages: ground induction coil detection, gate control and real-time parking space detection. Parking space detection is closely related to the level of detection technology, and the rapid development of sensors is the guarantee of the detection level. The basic architecture of the first two parking space detection systems is too large, and the installation is too cumbersome; in terms of reliability, real-time, accuracy, scalability, low energy consumption, and small amount of engineering, they cannot meet the needs of rapid development of parking lots.
WiFi is a short-range wireless technology that connects to the Internet through radio waves and is widely used in indoor wireless local area networks. The outstanding advantages of WiFi are: first, the radio wave coverage is wide, with a radius of about 100 m; second, the transmission speed of WiFi is very fast, which can reach 54 Mb/s; third, the entry barrier is low, as long as the terminal equipment that supports WiFi is available You can join the WiFi network according to certain permissions. In the parking space detection system, WiFi technology is used to collect and transmit the node parameters of the detection system, and to transmit and control the control signal, avoiding cumbersome data lines in the parking lot, which has a certain meaning in reducing costs and energy consumption, and makes the detection The scalability of the system is more flexible.
Radio Frequency IdenTIficaTIon (RFID) technology is a non-contact automatic identification technology realized by radio frequency communication. RFID in the 2.4 GHz frequency band can reduce the requirements for the corresponding equipment in the system and reduce the sensitivity to frequency deviation. The introduction of RFID technology into the parking space detection system is conducive to the development of standard equipment, and the uniqueness of the vehicle detector ID number can be used to quickly locate the parking space, which is conducive to parking space guidance in the parking lot.
In this paper, combining the requirements of parking lots for parking space detection systems, a WiFi-based RFID expandable AMR parking space detection system is designed, which greatly reduces the cost and complexity of the parking space detection system, reduces the energy consumption of the system, and improves the detection accuracy of the system And feasibility, to realize the scalability of the system.
1 System design
1.1 Design of parking space detection system
The parking space detection system consists of a server, a wireless router, a parking space display, an RFID reader and AMR (Anisotropic Magneto ResisTIve) sensor node. The server is responsible for processing the uploaded data, sending the processing results to the display, and is responsible for sending instructions to the reader. The wireless router is an important part of the entire parking space detection system, and it is responsible for forming all parts of the entire system into a local area network. The parking space display is used for real-time display of the current parking space. The RFID reader/writer receives the data uploaded by the AMR sensor node, transmits it to the server via WiFi, and also receives the server’s instructions and forwards it to the AMR sensor node. The AMR sensor node is responsible for detecting the magnetic field on the parking space, judging whether there is a vehicle according to the change of the magnetic field, reflecting the detected situation through data, and transmitting the data to the RFID reader, node and RFID reader through wireless means. Communication is two-way.
When designing the system, the system network structure is a star topology, the system RFID reader is a network controller, and the AMR sensor nodes are all slave nodes. The network topology is shown in the figure. The RFID reader has the function of sending and receiving, and is responsible for the management and control of the uplink and downlink data or instructions of the system; the AMR sensor node is responsible for the magnetic field parameter data collection and data preprocessing.
Network topology diagram
1.2 System circuit design
The circuit design of parking space detection system includes:
(1) AMR sensor node circuit, including node power supply part, parking space magnetic field acquisition part, data preprocessing part and radio frequency transceiver part, etc.;
(2) RFID reader circuit, including radio frequency transceiver part, WiFi part, data processing part and control part.
The basic circuit of the AMR sensor node is shown in the figure. The power supply part is played by TI’s APL5312-33 as the LDU function. The power supply input voltage is 4.2 V and the output is 3.3 V.
Basic circuit of AMR sensor node
Magnetic field strength detection uses MMC2122MG AMR sensor, which has the characteristics of small size, long life, high sensitivity, low energy consumption and stability. It can be widely used in electronic compass, GPS navigation, position sensing, vehicle detection and magnetic measurement. MMC2122MG is a two-axis magnetoresistive sensor. It can complete signal processing on the chip. It also integrates an I2C bus. It does not require A/D conversion and can be directly connected to the microprocessor.
Use the MSP430F2618 with low power consumption and high performance to preprocess the collected data, communicate with the 2.4 GHz radio frequency chip CC2500 through its built-in SPI port, and upload the preprocessed data packet to the RFID reader. Receive instructions from the RFID reader.
The physical object of the AMR sensor node is shown in Figure 4.
The radio frequency transceiver circuit of the RFID reader is shown in Figure 5. CC2500 communicates with the reader control part through SPI. CC2591 increases the link budget by providing a power transmitter to improve the output power; CC2591 has a low noise figure. Noise amplifier (LNA) to improve receiver sensitivity, also has power amplifier (PA), switch RF matcher and balun circuit, which can meet the simple design of high-performance wireless applications.
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