Design of WiFi-based RFID scalable AMR parking space detection system

introduction

Real-time detection of parking spaces in parking lots is the key to realizing intelligent management of parking lots and improving parking space utilization. It is also a requirement for modern parking management. The development of the parking space detection system in the parking lot has generally gone through three stages: ground sensing coil detection, gate control and real-time parking space detection. Parking space detection is closely related to the level of detection technology. The rapid development of sensors is the guarantee of detection level. The basic architecture of the first two parking space detection systems is too large and the installation is too cumbersome; they cannot meet the needs of the rapid development of parking lots in terms of reliability, real-time, accuracy, scalability, low energy consumption and small amount of Engineering.

WiFi is a short-range wireless technology that connects to the Internet through radio waves and is widely used in the establishment of indoor wireless LANs. The outstanding advantages of WiFi are: first, the coverage of radio waves is wide, with a radius of up to about 100 m; second, the transmission speed of WiFi is very fast, which can reach 54 Mb/s; third, the entry threshold is low, as long as the terminal device supports WiFi You can join the WiFi network according to certain permissions. In the parking space detection system, WiFi technology is used to collect and transmit node parameters of the detection system, and to transmit and control control signals. This avoids laying out cumbersome data lines in the parking lot, which has certain significance for reducing costs and energy consumption, and makes detection more efficient. The system's scalability is more flexible.

Radio Frequency Identification (RFID) technology is a non-contact automatic identification technology that uses radio frequency communication. RFID in the 2.4 GHz frequency band can reduce the requirements for corresponding equipment in the system and reduce the sensitivity to frequency deviations. The introduction of RFID technology into the parking space detection system is conducive to the development of standard equipment. The unique ID number of the vehicle detector can be used to quickly locate parking spaces, which is beneficial to parking space guidance in the parking lot.

This paper combines the requirements of the parking space detection system in the parking lot to design a WiFi-based RFID expandable AMR parking space detection system, which greatly reduces the cost and complexity of the parking space detection system, reduces the energy consumption of the system, and improves the system detection accuracy. and feasibility to achieve system scalability.

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 an AMR (Anisotropic Magneto Resistive) sensor node. The server is responsible for processing the uploaded data, sending the processing results to the display screen, and is responsible for sending instructions to the reader/writer. The wireless router is an important part of the entire parking space detection system. It is responsible for organizing all parts of the entire system into a local area network. The parking space display screen is used to display the current status of the parking space in real time. The RFID reader receives the data uploaded by the AMR sensor node and transmits it to the server through WiFi. It also receives the server's instructions and forwards them to the AMR sensor node. The AMR sensor node is responsible for detecting the magnetic field in the parking space, judging whether there is a vehicle based on the changes in the magnetic field, reflecting the detected situation through data, and packaging the data and transmitting it wirelessly to the RFID reader, node and RFID reader. Communication is two-way.

When designing the system, the system network structure is a star topology, the system RFID reader and writer is the network controller, and the AMR sensor nodes are all slave nodes. The network topology is as shown in the figure. The RFID reader has a transceiver function and is responsible for the management and control of the system's uplink and downlink data or instructions; the AMR sensor node is responsible for magnetic field parameter data collection and data preprocessing.

1.2 System circuit design

The parking space detection system circuit design 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/writer 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 uses TI's APL5312-33 to function as an LDU. The input voltage of the power supply is 4.2 V and the output is 3.3 V.

Magnetic field strength detection uses the MMC2122MG AMR sensor. This sensor has the characteristics of small size, long life, high sensitivity, low energy consumption and stability. It can be widely used in electronic compasses, GPS navigation, position sensing, vehicle detection and magnetometry. MMC2122MG is a two-axis magnetoresistive sensor. It can complete signal processing on the chip and integrates the I2C bus. It does not require A/D conversion and can be directly connected to the microprocessor.

The MSP430F2618, which has low power consumption and high performance, is used to preprocess the collected data, communicate with the 2.4 GHz radio frequency chip CC2500 through its own SPI port, and upload the preprocessed data packets to the RFID reader. Receive instructions from the RFID reader.

The RF 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, power amplifier (PA), switching RF matcher and balun circuit to meet the simple design of high-performance wireless applications.