In order to reduce the construction and operation cost of the urban-level parking induction system, a system architecture that does not need to establish a management control center, using LPC11C14 and CC2530 as an important part of the system in the system - regional ZigBee network. Through the experiment of the test system developed, the ZigBee network can accurately receive the parking request issued by the user's mobile phone, and can feed back the best parking space information from the user according to the parking space status, from the user sends a request to receive feedback information. Time does not exceed 10s.
The parking-inducing system is a multi-level information to be published as a carrier, which can provide information such as parking lot, parking space, and information systems such as the parking lot, guiding the driver's effective parking. Based on the size of the coverage, parking induced systems can generally be divided into two types and parking lots. In order to save the construction and operational cost of urban-level parking induced systems, this paper proposes a system architecture that does not require the establishment of a management control center. On this basis, this paper focuses on important components in the architecture - the hardware and software design of regional ZigBee networks.
1 research status
The parking-inducing system is a smart transportation system for mitigating the phenomenon of parking in the city. In the past 40 years of development, the development effect of NAC in 1971 was remarkable. my country's construction has risen in 2001, and the development of nearly 10 years has also achieved good results. After analysis, it was found that although there were various systems at home and abroad, their system structure and working principle were basically similar, all consistently consistently consisting of data acquisition, data transmission, central management, and data released. Therefore, it is necessary to build and maintain a city-level management control center. The operations also need long-term payment data acquisition and data release between the two parts and management controls, which leads to the construction of the system and the high cost of the operation.
2 system overall architecture
By deploying a "regional" ZigBee network in each outdoor parking lot and each of the roadside parking area, each outdoor parking area is separately deployed, and it can be completed in the entire city with the smartphone of the parking user. Realize parking-induced features. In the above architecture, there is no need to build a city-level management control center, which can greatly save the construction of the system and the post-operating costs. The design system architecture is shown in Figure 1, and its approximate workflow is:
Figure 1 A general structure diagram of a low-cost urban parking induction system
1) All terminal nodes of each ZigBee network periodically capture the parking space status information transmitted by the connected sensors.
2) If the collected parking position is different from the last state, the current parking position is sent to the adjacent router node, and the feedback of the coordinator node is waited. If you have not received feedback for more than a certain period of time, it is returned until feedback is received.
3) Each router node forwards the data of the received terminal node to the coordinator node.
4) After the coordinator node receives a message with changes in a parking position, feedback to the terminal node and updates the database.
5) When the car is driving to a certain point, the user triggers a smartphone to find a request for a parking space, and the prior installed smartphone software is operated according to the current location of the vehicle to determine the optimal parking lot (or roadside parking area) .
6) Smartphone software with the optimal parking lot (or roadside parking area), the coordinator node queries the current parking status database. If there is no vacant park, please feed back all the parking spaces to smartphone software; otherwise, the system runs the parking space search algorithm to determine the optimal parking space.
7) After determining the optimal parking space, the smartphone software first guides the vehicle to the destination parking lot (or the roadside parking area). Continue to guide the vehicle to the purpose of parking space.
3 hardware design of regional zigbee network
Regional ZigBee network consists of three types of coordinators, routers, terminals. The terminal node is responsible for the timing to collect parking status and transmit information change in the parking position; the router node is responsible for forwarding the status change information; the task of the coordinator node includes: receiving the parking status change information and updating the database, receive the user through smartphone Announced parking request, query the parking status in the database, run the parking space search algorithm, feedback to the user, and the best parking space information.
In the coordinator node, the following primary devices are required: 1) A embedded controller chip for managing embedded databases; 2) a ZigBee communication chip for communication with router node; 3) a GPRS module, used Communicate with the user's smartphone.
The embedded controller uses NXP's LPC11C14 chip. The chip uses a Cortex-M0 kernel processor with a maximum operating frequency of 50 MHz. In the memory, 32KB Flash and 8KB SRAM are configured; in terms of interface, there is a serial port, a 2-channel 10-bit ADC, two SPI interfaces, an I2C interface, a SWD interface, and the like.
The ZigBee communication chip uses N company CC2530. This chip is suitable for applications such as 2. GHz IEEE 802.15.4 and ZigBee. The interior of the chip includes a radio frequency transceiver, programmable flash, enhanced 8051MCU, 8KB RAM, etc. Since the time consumption from the sleep mode to the working mode is very short, the chip is particularly suitable for low power applications.
Since the internal connection inside the LPC11C14 chip does not contain an EEPROM, the AT24C02 chip is external to the I2C interface in the embedded database in the inside of the LPC11C14 chip. Communication between LPC11C14 and CC2530 is to communicate with serial ports. Because the LPC11C14 has only one serial resource, to implement serial communication of the LPC11C14 and the GPRS module, the SPI serial port chip MAX3100 is converted.
The GPRS module uses universal module SIM_300S. The power supply chip of the LPC11C14 board uses the MIC5209, the power supply chip of the CC2530 board adopts HT7533. The overall hardware block diagram of the coordinator node is shown in Figure 2.
Figure 2 Coordinator Node Hardware Structure
The hardware block diagram of the terminal node and the router node is very similar to the block diagram of the CC2530 in the coordinator node. The difference is that the terminal node is connected to a parking space detection sensor, and the terminal node and the router node are powered by lithium batteries.
4 Software Design of Regional ZigBee Network
The main program flow chart of LPC11C14 in the coordinator node is shown in Figure 3. First complete the initialization first after power-on. If the parking status change information transmitted by the CC2530 is received, feedback is sent to the CC2530, and the database is updated. If the parking request is received, it is judged that there is no vacant park according to the current state in the database. If there is a free parking space, run the parking space search algorithm to determine the optimal parking space. Thereafter, feedback from the user through the GPRS module.
Figure 3 Main program flow chart of LPC11C14
Figure 4 Main program flow chart of the coordinator CC2530
The main program flow chart of the CC2530 in the coordinator node is shown in Figure 4. After initialization, first determine whether the parking status change message is received. If you have not received, go to sleep; if you receive it, you will return from the sleep state to normal. Next, in order to prevent parking status, it is necessary to be temporarily stored in the Flash memory inside the CC2530. Thereafter, feedback is sent to the terminal node via the router node. Finally, send the change information to the LPC11C14 and wait for feedback. If you do not receive feedback within the specified time; if you receive feedback, you will enter the sleep state.
The main program flow chart of the terminal node is shown in Figure 5. After initialization, data acquisition of the parking space detection sensor is initialized, and the obtained data is converted through the A / D module comes with the CC2530, and then stores the Flash inside the CC3530 in a loop coverage. Thereafter, it is determined whether the current state is the same as the previous state. If the parking status changes, the zigbee RF module sends data to the coordinator node via the router node, and waits for feedback from the coordinator node. If there is no feedback of the coordinator node in the specified time, the data is retransmitted; if feedback is received, the time is turned on and then enters the sleep state. Next, wait until the timing interrupt wake up, perform the next data acquisition.
Figure 5 Main program flow chart of terminal nodes
Figure 6 Main program flow chart of router node
The main circuit diagram of the router node is shown in FIG. Then store the Flash inside the CC3530 in a loop covered. Then, the information change in the parking status is then sent to the coordinator node, and the feedback of the coordinator node is waited. If feedback is not received within a specified time; otherwise, forward the feedback sent by the Terminal Node Adjustment, after entering the sleep state, waiting for the external interrupt wake-up.
5 physical display and simulation results
Figure 7 is a real display diagram of the test system developed. In the middle upper portion of Figure 7, the left is the LPC11C14 board of the coordinator node, and the right side is the CC2530 board of the coordinator node. In the LPC11 C14 board, the part with an antenna on the left is a commercial GPRS module. In the CC2530 board, the middle upper portion is part of the antenna is commercialized ZigBee RF module. Since the frequencies of these two parts are in the microwave band, the commercial mature module is used to ensure reliability. In the middle and lower part of Fig. 7, the left is the router node, and the right is the terminal node. In order to ensure the test effect, the two nodes use the commercial ZigBee module when testing, and the bottom plate can be replaced with the bottom plate developed (ie: the bottom plate used in the CC2530 board in the current coordinator node). .
Figure 7 Test system real display diagram
In order to test the regional ZigBee network soft, hardware design validity, the test data as shown in Table 1 is deposited in the embedded database of the LPC11C14 board. Thereafter, the mobile phone request is proposed to the GPRS module of the LPC11C14 board with the mobile phone. Next, the LPC11C14 runs a parking space search algorithm. According to the data in Table 1, it concludes that the annual parking space is optimized. Then, the GPRS module of the LPC11C14 will then reply to the mobile phone. The send and reception interface of the SMS are shown in Figure 8. According to the results of the timing, the time from the trigger SMS send button to the received feedback does not exceed 10 seconds.
Figure 8 Display interface for mobile phone sends and receive information
Note: 1) When the current state is 0, it means that the parking space is occupied; the current state is 1, indicating the parking space. 2) When the occupation of the two-sided parking space is 0, it means that both the parking space is not occupied; 1, indicates that there is an occupation; 2, indicating that both sides are occupied.
6 conclusion
The embedded chip LPC11C14 and the ZigBee communication chip CC2530 are main components, and a hardware circuit for parking-induced regional ZigBee networks is designed, while developing control and communication programs for three-class nodes of coordinators, routers and terminals. Test experiments show that the ZigBee network designed can accurately receive user parking requests, and feedback to the best parking space information in time, from the user request to receive feedback, no more than 10 s.
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Source: Wiku Electronic City
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