Urban roads are staggered, vehicles are combed, and pedestrians are bustling. So what is it to achieve this order? It relies on the automatic command system of traffic lights. Traffic lights are an important command system for urban traffic. As an effective means to control traffic flow and improve road traffic capacity, traffic lights have obvious effects on reducing traffic accidents. This paper designs an intelligent traffic light system with STC89C52 single-chip microcomputer as the core and wireless control through Zigbee module remote control. Traffic police can realize the change of traffic light length by wireless remote control to adapt to different traffic conditions and crowds, and digital tube display The remaining time of the traffic lights fully reflects the control idea of ​​the Internet of Things and has certain application value and market prospects.
1, system designThe article designed a wireless control system for intersection traffic lights with the STC89C52 single-chip microcomputer as the core. The Zigbee module remote control is used to change the length of the traffic lights, and the two digital tubes are used to display the control status. The system mainly includes three parts: the handheld device module, the traffic signal control module and the digital display module. In the actual traffic scene, the distance from the center of the intersection to the traffic lights is generally no more than 300 meters, and the communication distance of the Zigbee module can be reliably transmitted within 800 meters. By constructing the Zigbee network into a Mesh network structure, nodes can also forward data, further enhancing the reliability of the system. Traffic police at the center of the intersection can be connected directly to the traffic light module via a handheld device.
Figure 1 Wireless terminal layout
2, system hardware design 2.1, wireless handheld device hardware designThe hardware of the handheld device mainly includes a single chip microcomputer, a liquid crystal display, a wireless communication, a clock control module, etc., as shown in FIG. 2 . After the traffic police inputs the signal and time to be controlled through the button circuit, it is packaged by the MCU and sent to the traffic light control module through the Zigbee module. Among them, CN3065 is used for system calibration and time prompt, Zigbee module uses cc2430.
Figure 2 Wireless handheld device hardware topology
2.2, traffic light control module hardware designThe main function of the traffic light control module is to identify the data packet and issue a control command to switch the signal light. The serial communication is used to connect with the microcomputer to transmit the field data to the city monitoring center, which is convenient for the city monitoring center to perform remote control under special circumstances. In traffic lights at intersections, the traffic lights in the same road are shown to be identical. Therefore, the digital tube display circuit uses two common anode seven-segment digital tubes, two in one group, and one digital tube can display numbers between 0 and 99. Each pin of the P1 port of the STC89C52 is connected to a resistor of 300 ohms, and then connected to a seven-segment digital tube.
Figure 3 Traffic light control module hardware topology
3, system software designThe software design of the system includes two parts: software design of the handheld device and software design of the traffic light control module. The article develops software programs for handheld devices and signal control modules based on the IAREmbeddedWorkbench development platform.
3.1, handheld device software designThe main function of the handheld device is to let the traffic police input the traffic signal ID and status to be controlled and send the control signal. The wireless communication module CC2430 has a protocol stack Z-STACK conforming to the Zigbee specification. The Zigbee module of the handheld device is a coordinator whose main function is to start the Zigbee network and update the network node, so that the control can be performed only when the handheld device is activated. In order to prevent the malfunction and refusal caused by the packet loss, the data packet adopts the MODBUS protocol, and the check mode selects CRC-16. After the Zigbee network is established, the latest list of semaphores that can be controlled is displayed on the LCD. After the traffic police enters the command, the control information is sent out.
Figure 4 Handheld software communication flow chart
3.2. Traffic Light Control Module Software DesignThe main function of the traffic light control module is to join the established Zigbee network of the handheld device and receive the control commands sent by the handheld device. When applying to join the network, send your ID number and date to the handheld terminal to facilitate unified school time. If it is not added to the Zigbee network, it will be executed according to the original traffic light control logic.
Figure 5 control module flow chart
4 ConclusionThe article starts with the actual demand of the traffic police to control the traffic lights, combined with the control idea of ​​the Internet of Things, designed a set of traffic police wireless handheld traffic light control system. Through the Zigbee network, the system can transmit the control information of the traffic police to the control module, and finally realize the demand for the traffic light of the traffic police on duty. The whole system is designed with low power consumption and low cost. The work is stable and reliable, and the wireless network is flexible and reliable, which is suitable for large-scale promotion.
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