**1. Introduction**
Urban traffic congestion is becoming increasingly severe, posing significant challenges to urban mobility and road efficiency. To address this issue, optimizing traffic signal control has become a critical task. However, traditional traffic light systems rely on fixed-time control methods, which are unable to dynamically adjust the green light duration based on real-time traffic conditions. This inflexibility leads to inefficient use of road resources and contributes to unnecessary delays.
To tackle these problems, an adaptive traffic light control system based on a wireless sensor network has been developed. This system uses ultrasonic transceiver modules embedded in sensor nodes installed on each lane to detect vehicle flow. The collected data is transmitted wirelessly to a centralized controller, which processes the information and runs a scheduling algorithm to adjust the traffic light timings accordingly. This approach enhances road utilization by adapting to real-time traffic demands.
The wireless communication between the controller and sensor nodes eliminates the need for physical wiring, making installation more flexible and cost-effective. These densely distributed sensor nodes can accurately monitor the number of vehicles and the occupancy of each lane, providing reliable data for intelligent traffic management. Additionally, the system ensures robustness by allowing the controller to switch to a pre-set timing mode if wireless communication is disrupted, preventing system failure.
**2. System Design**
As illustrated in Figure 1, the system comprises three main components: the centralized controller, wireless sensor nodes, and traffic lights. It supports communication with a remote monitoring computer via a metropolitan area network, enabling both data transmission and remote control commands.
The centralized controller serves as the core of the system, responsible for communicating with the sensor nodes, running the scheduling algorithm, controlling the traffic lights, and interfacing with the remote monitoring system. Due to its high performance requirements, it is built using an ARM processor.
Wireless sensor nodes are essential for collecting traffic data. Each node is equipped with multiple ultrasonic transceivers to detect vehicles. While they can be powered via cables or batteries, battery-powered nodes require higher maintenance costs.
The traffic lights are standard devices placed at intersections, with no special modifications required. The wireless communication between the controller and the sensor nodes significantly reduces installation complexity. In contrast, a wired connection is used between the controller and the traffic lights to ensure reliability during potential radio interference.
**3. Hardware Design**
**3.1 Wireless Sensor Node Design**
The wireless sensor node consists of three parts: the processor board, backplane, and sensor board. The hardware architecture is shown in Figure 2.
**3.1.1 Processor Board Design**
The processor board is built around the CC2430 chip, which integrates an RF transceiver and a microcontroller. It offers low power consumption, strong anti-interference capabilities, and support for various power modes. To enhance transmission range, an RF power amplifier (CC2591) is added, increasing the transmit power to 18 dBm and extending the communication distance to 500 meters.
**3.1.2 Ultrasonic Sensor Board Design**
The sensor board includes an ultrasonic transmitter, receiver, and associated circuits. The transmitter uses a piezoelectric ceramic sensor T:40:12, while the receiver uses a paired R:40:12. The transmitting circuit employs the LM386 amplifier, offering adjustable gain and low power consumption. The receiving circuit uses the CX20106 infrared detector, which can also function as an ultrasonic sensor due to its adjustable center frequency. The internal circuit is shown in Figure 4.
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