Realization of motor vehicle parking lot control management system solution through automation network
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The networked motor vehicle parking lot control and management system makes full use of the highly decentralized nature of the modern Internet network, no matter the scale of the expansion system. The convenience of users has been maximized. The bottom equipment is connected through the already mature RS 485 industrial bus, which has the characteristics of high reliability and low development cost. Through the collection of sensor data, the user is allowed to enter the parking lot to park the parking space in a simple, safe and efficient environment. The user is completely self-service to the parking lot, and the management of the parking lot is also monitored by the computer automatically.
1 System scheme design
The system is divided into three modules: network, upper computer, and lower computer. The system structure is shown in Figure 1.
Network module The network module refers to the network connection of each management machine or server host through the network adapter, and the user makes reservations for parking spaces and online payment through the webpage. A large-scale parking lot management system can be built through computer management, which is suitable for modern large-scale property companies to centrally and uniformly manage multiple geographically distributed parking lots; RS 485 serial communication bus is used to add parking lot execution units, such as monitoring hosts , Access control machines, toll collection machines, identification equipment and other low-speed equipment, and communicate with the upper computer.
The upper computer module refers to the management computer of each distributed parking lot or the expanded server. Manage the parking lot database through the management software, receive the user’s network reservations and the administrator’s management, communicate with the lower computer after the signal level is converted to the RS 485 communication level through the RS 232 communication interface, and control the various execution units of the parking lot , The upper computer is connected with the closed-circuit image monitoring unit to monitor the real-time safety dynamics of the parking lot.
The lower computer module parking space monitoring unit is composed of a monitoring main controller composed of two single-chip microcomputers and a hot backup machine; the parking space monitoring circuit composed of photoelectric sensors is controlled by the photoelectric coupling module to monitor the parking space in real time; due to the use of bus technology, the parking space of the parking lot The number can be expanded according to needs. The access control unit includes a single-chip microcomputer, real-time clock, memory, LCD display, keyboard, and control output circuit. The hot backup machine is running out of time. The identity recognition unit for warehouse entry and exit includes radio frequency identification and infrared barcode identification, which are used to identify the user’s identity information. An automatic charging unit is connected to the bus, which is similar to the current vending machine.
2 Circuit design of lower access control machine
The access control module of the lower-level computer is the first and last link of entering and exiting the parking lot. Only when the design structure is reasonable and the humanized system is used will it be welcomed. The module adopts a modular design and consists of a power supply circuit, a control machine host, an access control clock circuit, a parking space information storage circuit, an access control communication circuit, an access control execution control circuit, an access control information input circuit, an access control information output circuit, etc. The structure block diagram is shown in the figure 2 shown.
2.1 Main circuit of access control machine
The controller chip adopts the low-power, high-performance CMOS 8-bit microcontroller AT89S51 produced by Atmel, USA. The chip contains a 4 KB instruction system. It is not only used in many cost-effective circuits, but also can be flexibly used in various control fields. , So its control core uses AT89S51 chip. The working principle of the main circuit of the control machine is shown as in Fig. 3.
To control the external clock of the host, the system uses serial communication, the baud rate of communication is set to 9 600 b/s, 11.059 2 MHz quartz crystal is selected, and two fine-tuning capacitors between 20 and 30 pF are connected to form the clock source. The effective reset circuit of the single-chip microcomputer adopts two methods: the power-on reset of the single-chip microcomputer and the manual level reset of the single-chip microcomputer. According to the data of AT89S51, the reset time is when the RST pin appears at a high level for more than two machine cycles to reset the single-chip microcomputer. Choose 11.059 2 MHz crystal oscillator to confirm that its machine cycle is less than 1μs, so choose a power-on reset circuit with a capacitance of 22μF and a resistance of 1 kΩ, and use a manual level reset to choose a 200 Ω resistor. Use a resistance of 10 kΩ as a pull-up resistor at port P0. Liquid crystal LCD display uses P0 port; input keyboard uses P1 port; part of P2 port is used for the control pin output of liquid crystal display, and the rest is used to connect access control motor drive signal or alarm signal drive terminal; part of P3 port is used for clock and data storage The I2C pins of the chip are pulled up by resistors, some are connected to TTL-RS 485 circuits for communication, some are used for interrupts, and the excess is used for output control.
Because the access control machine part is connected with a clock circuit and an information storage circuit, another important use of this circuit is to be used as a hot backup machine (hot standby) for temporary emergency control when the upper computer (PC) recovers from a short-term failure. machine).
2.2 Access control machine information storage circuit
If the equipment is running during the peak parking time, it may cause the system to have all the lower equipment accessing the upper computer at the same time, which will cause the system network communication blockage and cause the system monitoring failure and other phenomena. Therefore, adding an information storage circuit to the access control machine can effectively buffer the communication pressure and avoid communication jams. At the same time, the information storage part can be used as a temporary upper computer and a hot backup machine. Even if the upper computer fails for a short time and stops, the monitoring operation of the system is still normal. Such a small redundancy design allows the upper and lower computers to operate complementarily, and the software and hardware complement each other.
The access control system is divided into front/rear access control modules. The circuit design of the front/rear access control module is the same, but the purpose and program are different, and the information stored in the system is also different. The front access control mainly stores parking space information and usage conditions, and the rear access control stores parking space passwords, parking time, amount and other information. The storage density of integrated information uses AT24C08A or AT24C16A as the storage unit. In the design, the address line can be adjusted as needed. The design is to ground the address line. Write permission to ground valid.
2.3 Access control machine information display circuit
The information output of the access control machine can be through two ways, the display output of the control machine and the main screen output of the host computer. The output of the control machine can be used as a backup display screen for host computer failure for temporary use. The LCD liquid crystal display module is used for output in the design. A general liquid crystal display module has 8 data transmission pins and 5 to 8 control pins. The rest are the LCD background power supply and display brightness adjustment pins, which only need to be connected. Use RTl2032 dot matrix liquid crystal display in this design.
2.4 Access control machine information input device circuit
The entry of access control information uses an access control identification system, such as a radio frequency identification module and an infrared barcode identification module. However, it is also possible to enter a password form, which can provide more than one authentication system and can be used flexibly. The information input device uses a 4×4 matrix scanning keyboard, 12 keys are used as input numbers for confirmation and re-entry, and 4 keys are disconnected from the control machine and used as function keys. For example, storage, retrieval, alarm, failure, etc., and use diode isolation to prevent interference.
2.5 Access control machine communication interface level conversion circuit
In the design, the units involved in the RS 485 industrial bus must perform level conversion, which mainly refers to TTL-RS 485 level conversion and RS 232-RS 485 level conversion. Among them, RS 232-RS 485 level conversion is divided into RS 232-TTL, TTL-RS 485 two conversion parts.
Use MAX232 to design RS 232 to TTL level conversion circuit, the power supply in the circuit uses serial port power technology, and the light-emitting diode is used as the power supply and communication indicator in the circuit.
The TTL-RS 485 level conversion circuit is designed with a MAX 485 series integrated circuit that meets the RS 485 communication level standard. The circuit is shown in Figure 4.
When sending data, the data stream flows into the TXD port, after level conversion by MAX 485, the RS 485 high or low differential level signal is output through J6; when receiving data, the RS 485 high or low differential level signal passes After J6 enters the MAX 485 for level conversion, the TTL level signal flows out through the RXD port. As long as the program can ensure that the receiving and sending operations are not performed at the same time, it is guaranteed to transmit data in half-duplex. The program does not need to use instructions to control DE/RE to switch between receiving and sending. The conversion is completed by the hardware circuit itself.
2.6 Execution circuit design of access control machine
Use the I/O port of the access control machine to control the drive signal level. The actuator of the access control machine receives the access control signal, drives the motor to act, controls the opening and closing of the access control, and controls the entry and exit of the vehicle. The MOSFET is connected to form an H-bridge to drive the DC motor, and a diode is connected in parallel at both ends of the MOSFET as a sequence current diode to effectively protect the MOSFET and prolong the life of the device.
3 Circuit design of lower locomotive parking space monitoring control machine
The lower locomotive parking space monitoring module constitutes the feedback link of the closed-loop monitoring system. Its design directly affects the stability of the system and is a key link of the parking lot management system. This part also adopts a modular design, which can be specifically divided into a monitoring power supply circuit, a monitoring control machine main circuit, a monitoring coupling circuit, a parking space monitoring and display circuit, and a control machine communication circuit. The principle block diagram is shown in Figure 5.
The design of the level conversion circuit of the communication interface of the monitoring control machine is the same as the design of the level conversion circuit of the communication interface of the access control machine. The power supply of the real-time monitoring and display circuit of the parking space should be designed independently to avoid interference from external signals.
The parking space monitoring control machine circuit also uses the AT89S51 single-chip microcomputer as the controller, but every 64 parking spaces uses two single-chip microcomputers to form the host and hot backup machine structure. Use the P0 and P2 ports of the single-chip microcomputer to form an 8×8 matrix scanning circuit to monitor 64 parking spaces. The P1 port is used as the input port for parking lot status monitoring, and the serial port of the single-chip microcomputer (P3.0, P3.1) is connected with MAX 485 to convert between TTL level and RS 485 level. When the host is working, the hot backup machine enters the dormant state. The function of the monitoring display circuit is to display and feed back the parking space information, which is composed of sensors, seven-segment digital tubes and other components.
Because the photoelectric sensor is affected by dust and installation environment, and considering the high cost of mass production. Therefore, a single-pole double-throw switch is selected as the detection sensor in the system. The mechanical monitoring method has the advantages of stable operation and long life, can be buried in the ground, and is less affected by the external environment. The micro switch is placed in the cylinder, and the light-emitting diode is placed in the square groove and covered with glass to indicate the parking condition. The single-pole double-throw switch is laid on the front tire of the car, and the switch is switched by the gravity of the vehicle. The monitoring display circuit and the monitoring control machine are connected through a signal coupling circuit. The signal coupling circuit uses a photocoupler (model: PLP521), which can well isolate external interference and ensure that the control circuit’s parking information identification is accurate and stable. The block diagram of the parking space monitoring circuit is shown in Figure 6.
In Figure 6, the control circuit power supply of the parking monitoring module and the monitoring display circuit power supply are designed separately to prevent external interference signals during long-distance signal transmission. This is also the purpose of circuit isolation using optical coupling devices. The monitoring display circuit should use a 5 V power supply with a large current output capability to ensure that the display brightness of each parking space is sufficient.
4 System test
The computer virtual demonstration of the vehicle exit/entry prohibition process is shown in Figure 7. After the vehicle enters the access control, it passes the entrance access control identity verification, including infrared barcode scanning, radio frequency card recognition, touch screen soft keyboard or single-chip hard keyboard for identity recognition and then enters the parking space. After the vehicle is in place, it monitors the display circuit action and switches the signal. When the vehicle leaves the garage, the parking space indication circuit will act again, and then the exit access control machine will identify the vehicle in the same way as the entrance access control, and then pay the vehicle to release the vehicle. Each step of the entire work process will be carried out under the full monitoring of the system. Database parking lot The event table records data in real time.
5 Conclusion
The design of the parking lot management system is a closed-loop management and control system that combines single-chip microcomputer technology, computer software technology and network technology, which can comprehensively monitor the dynamics of parking spaces and the operation of the parking lot. The system is simple to control, stable and reliable in work, low in data error rate, and wide in control range. It is a system with modular design, self-checking and self-recovering capabilities, multiple information input types, and multiple display output types. At the same time, the system uses a modular design, which is easy to expand. The system reserves sufficient interface space, which can be connected with the current public security department security system to realize the full use of public security resources. Users can stop at any time, book online, and have various settlement methods. The system is highly user-friendly. It can not only charge by time, but also set free parking time and other functions.
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