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 in urban lighting. The primary task of road lighting is to provide safe and comfortable lighting brightness on the basis of saving public energy, so as to reduce traffic accidents and improve transportation efficiency. Due to the limitations of the infrastructure, there is currently a lack of street-level communication links. Street light control methods generally only control the entire road in a unified manner, and cannot measure and control every light. Based on the Internet of Things, this paper designs an embedded wireless street lamp control module to realize the wireless autonomous networking of each street lamp, so that each street lamp can be telemetered and remotely controlled, and some units in the street lamp facility (such as electronic ballast Device, etc.) to achieve steplessly adjustable brightness (or illuminance) of street lamps from 30% to 100%. Under the condition of ensuring road lighting quality, improving identification and visual comfort, according to the ambient light intensity and time period, saving electricity 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 light, they make their own network, accept the command of the control center and feed back the status of the street light to the control center; HG-2 control The box uses ZigBee technology to communicate with all street lamps under the jurisdiction of the road, and uses GPRS to communicate with the control center. According to the instructions or time of the control center and the brightness of the sunlight, each box is issued a control command (street lights on, off, illumination (power level), 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 uses a 3D design, which is observed and controlled from a bird’s-eye view through zoom transformation. The lighting situation of the 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 telemetry and remotely controlled through the control center.
3 wireless communication module
3.1 Module design
The MCU of the wireless communication module is MC13213 of Freesclae Company. MC13213 adopts SiP technology to integrate MC9S08GT main control MCU and MC1320x RF transceiver in 9 & TImes; 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. 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 self-organized network of any street lamp node within its coverage area. In addition to achieving the connection of the street lamp, it also has adjustment The power output of the electronic ballast (30% to 100%) realizes energy saving and green lighting, detects the current, voltage, power factor of the power supply line, and the working status of each lamp. When a failure occurs (such as lamp damage, lamp When the rod hits or is damaged by man-made damage), it can alarm the monitoring center and relevant departments in real time.
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 (connecting two wires to achieve street lamp-level wireless control, removing two The root line is restored to its original state), and can be embedded in different positions of the street lamp (the bottom of the lamp post, the lamp post, and the lampshade).
3.2 Communication protocol
The communication protocol of the wireless communication module is as follows: the lighting is numbered in order of road segments, and "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 (bitmaps can represent up to 256 frames). If a node receives a command frame, it determines whether the frame has been forwarded by the node, such as If it has been forwarded, the frame is discarded (the node only forwards the received command frame without modifying the content of the frame), thereby ensuring the fastest speed of controlling a line, and effectively preventing the failure of a node from affecting the entire line The work of the line; the status return mechanism: after the command frame is sent to the designated node, the designated node receives the command and immediately returns to the state; forwarding rules: only the node number is smaller than the target node number, the status return process is reversed.
3.3 Connection with central monitoring
A transmission communication link is composed of several ZigBee nodes, and a cluster node is set in the middle of these nodes (one or more cluster nodes can be set on a road). Its function is to communicate with the control center by GPRS (command acceptance and Status returns), 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 is built using the commonly used V2ColdFire core, and its performance is up to 76MIPS (Dhrystone2.1) at 80MHz. The interface functions include: 1 MiniUSB interface, support 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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