Design a parking induction system using embedded chips and Zigbee communication chips

In order to reduce the construction and operation costs of city-level parking guidance systems, a system architecture is proposed that does not require the establishment of a management control center. LPC11C14 and CC2530 are used as core chips to design an important component of the system - a regional Zigbee network. Through the experiments of the developed test system, it is shown that the Zigbee network can accurately receive parking requests sent by users’ mobile phones, and can feedback the best parking space information to the user according to the status of the parking spaces in the parking lot. From the time the user sends the request to the time when the feedback information is received, The time does not exceed 10s.

The parking guidance system is an information system that uses multi-level information release as a carrier to provide real-time information such as the location, number of parking spaces, and parking space status of the parking lot to guide drivers to park effectively. According to the size of the coverage area, parking guidance systems can generally be divided into two types: city level and parking lot level. In order to save the construction and operation costs of city-level parking guidance systems, this article proposes a system architecture that does not require the establishment of a management control center. On this basis, this article focuses on the hardware and software design of the regional Zigbee network, an important component of the proposed architecture.

1 Research status

The parking guidance system is an intelligent transportation system used to alleviate parking difficulties in cities. It first appeared abroad in Aachen, Germany in 1971, and has achieved remarkable development results in the past 40 years. my country's construction began in 2001, and the development in the past 10 years has also achieved good results. After analysis, it was found that although various systems at home and abroad have their own characteristics, their system structures and working principles are basically similar, and they are roughly composed of four parts: data collection, data transmission, central management and data release. Therefore, a city-level management control center needs to be built and maintained, and the operation department also needs to pay long-term communication fees between the data collection and data release parts and the management control center, resulting in higher system construction and later operation costs.

2 Overall system architecture

By deploying a "regional" ZigBee network in every indoor parking lot, every outdoor parking lot and every roadside parking area in the city, and cooperating with parking users' smartphones, it can complete the entire city. Realize the function of parking induction. In the above architecture, there is no need to build a city-level management and control center, which can greatly save system construction and later operation costs. The designed system architecture is shown in Figure 1, and its general workflow is:

Figure 1 The overall structure diagram of a low-cost city-level parking guidance system

1) All terminal nodes of each ZigBee network regularly collect parking space status information from connected sensors.

2) If the collected parking space status is different from the last status, send the current parking space status to the adjacent router node and wait for feedback from the coordinator node. If no feedback is received after a certain period of time, it will be resent until feedback is received.

3) Each router node forwards all received data from the terminal node to the coordinator node.

4) After receiving the parking space status change message, the coordinator node sends feedback to the terminal node and updates the database.

5) When the car drives to a certain place, the user triggers the smartphone to make a request to find a parking space. The pre-installed smartphone software runs a parking lot optimization algorithm based on the current location of the vehicle to determine the optimal parking lot (or roadside parking area). .

6) The smartphone software communicates with the coordinator node of the optimal parking lot (or roadside parking area), and the coordinator node queries the current parking space status database. If there are no free parking spaces, information that all parking spaces are full will be fed back to the smartphone software; otherwise, the system will run a parking space optimization 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 roadside parking area). Then continue to guide the vehicle to the destination parking space.

3 Hardware design of regional Zigbee network

The regional Zigbee network consists of three types of nodes: coordinator, router, and terminal. The terminal node is responsible for regularly collecting the parking space status and sending out the parking space status change information; the router node is responsible for forwarding the parking space status change information; the coordinator node's tasks include: receiving the parking space status change information and updating the database, and receiving the user's information via smartphone Send a parking request, query the parking space status in the database, run the parking space optimization algorithm, feedback the best parking space information to the user, etc.

In the coordinator node, the following main components are required: 1) an embedded controller chip for managing the embedded database; 2) a Zigbee communication chip for communicating with the router node; 3) a GPRS module for for communicating with the user’s smartphone.

The embedded controller uses NXP's LPC11C14 chip. The chip uses a Cortex-M0 core processor and operates at a frequency of up to 50 MHz. In terms of memory, it is configured with 32kB FLASH and 8KB SRAM; in terms of interfaces, it is configured with a serial port, a 2-channel 10-bit ADC, two SPI interfaces, an I2C interface, a SWD interface, etc.

The Zigbee communication chip uses n company's CC2530. The chip is suitable for applications such as 2.4 GHz IEEE 802.15.4 and Zigbee. The inside of the chip includes a radio frequency transceiver, programmable flash memory, enhanced 8051MCU, 8KB RAM, etc. Since the transition from sleep mode to active mode takes very little time, the chip is particularly suitable for low-power applications.

Since the LPC11C14 chip does not contain EEPROM inside, in order to store the parking space status data in the embedded database, the AT24C02 chip is externally connected through the I2C interface. The communication between LPC11C14 and CC2530 is designed to use the serial port for communication. Because LPC11C14 has only one serial port resource, in order to realize the serial communication between LPC11C14 and GPRS module, the SPI to serial port chip MAX3100 is used for conversion.

The GPRS module uses the universal module SIM_300S. The power chip of the LPC11C14 board uses MIC5209, and the power chip of the CC2530 board uses HT7533. The overall hardware block diagram of the coordinator node is shown in Figure 2.

Figure 2 Coordinator node hardware structure diagram

The hardware block diagram of the terminal node and router node is very similar to the block diagram of the CC2530 in the coordinator node. The main difference is that the terminal node is connected with a parking space detection sensor. In addition, the terminal node and 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. After power-on, initialization is completed first. If the parking space status change information sent by CC2530 is received, feedback will be sent to CC2530 and the database will be updated immediately. If a parking request is received, it will be determined whether there are free parking spaces based on the current status of the parking spaces in the database. If there are free parking spaces, run the parking space optimization algorithm to determine the optimal parking space. Afterwards, the results are fed back to the user through the GPRS module.

Figure 3 Main program flow chart of LPC11C14

Figure 4 Main program flow chart of coordinator CC2530

The main program flow chart of CC2530 in the coordinator node is shown in Figure 4. After initialization, first determine whether the parking space status change message is received. If it is not received, it will enter the sleep state; if it is received, it will return to the normal state from the sleep state. Next, in order to prevent the parking space status from being lost before being stored in the database, it needs to be temporarily stored in the Flash memory inside the CC2530. Afterwards, feedback is sent to the terminal node through the router node. Finally, send the parking space change information to LPC11C14 and wait for feedback. If no feedback is received within the specified time, it will be retransmitted; if feedback is received, it will enter sleep state.

The main program flow chart of the terminal node is shown in Figure 5. After initialization, data is collected from the parking space detection sensor. The obtained data is AD converted by the A/D module that comes with the CC2530, and then stored in the FLASH inside the CC3530 in a cyclic overlay manner. Afterwards, determine whether the current state is the same as the previous state. If the parking space status changes, the Zigbee radio frequency module sends data to the coordinator node through the router node and waits for feedback from the coordinator node. If no feedback from the coordinator node is received within the specified time, the data will be retransmitted; if feedback is received, the timer interrupt will be enabled and the system will enter the sleep state. Next, wait for the scheduled interrupt to wake up and conduct the next data collection.