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1 Introduction
With the development of urban economy and scale, various types of roads are getting longer and longer, the number of motor vehicles is increasing rapidly, and the traffic flow at night is also increasing. The quality of road lighting directly affects traffic safety and urban development. How to improve the quality of road lighting, reduce energy consumption, and achieve green lighting has become a key issue for urban lighting. The primary task of road lighting is to provide safe and comfortable lighting brightness on the basis of saving public energy to achieve the purpose of reducing traffic accidents and improving transportation efficiency. Due to the limitations of the infrastructure, there is currently a lack of street lamp-level communication links. The street lamp control method generally can only control the entire road in a unified way, and it is impossible to measure and control each lamp. Based on the Internet of Things, this paper designs an embedded wireless street lamp control module, which realizes the wireless autonomous networking of each street lamp, so that each street lamp can be remotely measured and remotely controlled, and is connected to some units in the street lamp facility (such as electronic ballast The brightness (or illuminance) of the street lamp is infinitely adjustable from 30% to 100%. Under the condition of ensuring the quality of road lighting, improving the recognition reliability and visual comfort, according to the ambient light intensity and time period, it can save electric energy by 20～ 30%.
2 System structure
The structure of the road lighting system based on the Internet of Things is shown in Figure 1. By embedding a wireless communication module in each street lamp, making them self-organize the network, accept the command of the control center and feedback the state of the street lamp to the control center; HG-2 control The box uses ZigBee technology to communicate with all street lights on the road under its jurisdiction, and uses GPRS to communicate with the control center. According to the control center’s instructions or time and daily illuminance, it sends control commands to each street light (street lights on, off, illuminance (power size), etc. ), automatically adjust the power balance of the entire road; the control center is composed of a server, a large-screen display, and the CenterView central control system software platform. The CenterView central control system software platform adopts a 3D design. The lighting conditions of an entire city, a street, a road, or even a street lamp; mobile computing tools (laptops, PDAs, mobile phones) and street lamp maintenance vehicles can also be remotely telemetered and controlled through the control center.
3 Wireless communication module
3.1 Module design
The MCU of the wireless communication module is Freesclae’s MC13213. The MC13213 uses SiP technology to integrate the MC9S08GT master MCU and MC1320x radio frequency transceiver in a 9×9mm LGA package. MC13213 has 4KB RAM, 60KB FLASH, 1 serial peripheral interface (SerialPeripheralInterface, SPI), 2 asynchronous serial communication interfaces (SerialCommunicationsInterface, SCI), 1 keyboard interrupt module (KeyboardInterrupt, KBI), 2 Timer/Pulse Width Modulation Module (Timer/PWM, TPM), an 8-channel 10-bit analog-to-digital converter (Analog/DigitalConverter, ADC), and up to 32 GPIO ports, etc. as shown in picture 2.
The wireless communication module adopts ZigBee technology, IEEE802.15.4 protocol, and the communication coverage radius can reach 150m. It can communicate with any street lamp node in its coverage area by self-organizing network and communication. In addition to realizing the object-to-object connection of the street lamp, it also has adjustment The power output of the electronic ballast (30%～100%) can realize energy saving and green lighting. It can detect the current, voltage, power factor and the working status of each lamp of the power supply line. When rod impact, man-made destruction), real-time alarm to the monitoring center and related departments and other functions.
The wireless communication module is also designed for rain, moisture, lightning, and electromagnetic interference, and fully considers the convenience of installation, simple maintenance and recoverability (the two wires are connected to achieve street lamp-level wireless control, and the removal of the two The root wire returns to its original state) and can be embedded in different positions of the street lamp (the bottom of the lamp pole, the inside of the lamp post, and the inside of the lamp shade).
3.2 Communication protocol
The communication protocol of the wireless communication module is as follows: the lighting is numbered according to the order of the road sections, and the “hand in hand” communication between nodes is realized through command forwarding and status return. Command forwarding mechanism: each node uses a bitmap structure to record which frames have been forwarded (the bitmap can represent up to 256 frames), if the node receives the command frame, it will determine whether the frame has been forwarded by the node, such as If the frame has been forwarded, the frame is discarded (the node only forwards the received command frame and does not modify the content of the frame), thus ensuring the fastest control of a line, and effectively preventing a node failure from affecting the entire line The work of the line; state return mechanism: after the command frame is sent to the designated node, the designated node will receive the command and return to the state immediately; forwarding rule: only the node number is smaller than the target node number before forwarding, and the state return process is reversed.
3.3 Connection with central monitoring
A transmission communication link is composed of several ZigBee nodes. A cluster node is set in the middle of these nodes (one or more cluster nodes can be set on a road), and its function is to communicate with the control center in GPRS mode (command acceptance and Status return), the cluster node uses Freescale’s 32-bit CodeFire series MCF52223 chip as the control unit, and GTM900B (Huawei GPRS communication module) and EM770W (Huawei WCDMA 3G communication module) as the long-distance wireless communication module. The MCF5222x series are built using the commonly used V2ColdFire core, and the performance is up to 76MIPS (Dhrystone2.1) at 80MHz. The interface functions include: 1 MiniUSB interface, supporting USBOTG function, 3 2-wire serial ports, 1 microphone input interface, 1 HEADSET input/output interface, 1 HANDSET input/output interface, 1 8Ω/16Ω speaker output interface, 1 132*96 dot matrix LED, 1 5*5 key keyboard, support RTC, ADC, PIT&GPT, PWM Etc.; GTM900B and EM770W complete long-distance GPRS communication.
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