With the rapid development of highways, car speeds are increasing, traffic volume is growing, and car collisions are becoming more frequent. Statistical analysis of highway traffic accidents reveals that among the driver, car, and road, the driver is the least reliable link, especially at high speeds. Over 80% of accidents are caused by drivers' delayed reactions or misjudgments. This paper studies a rear-end collision prevention distance measurement and warning device using advanced lidar ranging technology, 32-bit embedded system (ARM) technology for data processing, and a 16-bit microcontroller with powerful voice storage capabilities (128 seconds) to provide voice prompts and sound and light alarms. This device assists drivers at high speeds in real-time monitoring of vehicles ahead, maintaining a safe driving distance and preventing rear-end collisions. 1. Device Design Principle Figure 1 shows the schematic diagram of the device. First, the distance between vehicles is measured by a laser radar rangefinder. The analog signal is transmitted to the A/D converter in the embedded system's RAM via a data cable, and then the digital signal is sent to an 8-bit CMOS memory. One signal is sent to an LCD display, directly showing the actual distance in meters. The driver can see the accurate distance display, which helps them make judgments and take effective measures. The other signal collects and analyzes data from the vehicle speed sensor, and after comparing the actual distance with the safe distance, sends a signal to a 16-bit Lingyang microcontroller to issue a voice alarm "Caution!" or "Danger!", simultaneously emitting an alarm sound or flashing a warning light to alert the driver. The vehicle speed sensor is a magnetoelectric sensor, outputting an alternating current signal. Magnetoelectric sensors are widely used in various automobiles in Europe, North America, and Asia. 2 System Design and Implementation Clearly, the most important part of this ranging device is distance measurement. Currently, the commonly used technologies for determining the safe distance to a car are ultrasonic ranging, microwave radar ranging, and laser ranging. Ultrasonic ranging utilizes the reflection characteristics of ultrasonic waves. An ultrasonic generator continuously emits 40kHz ultrasonic waves, which are reflected back after encountering an obstacle. The ultrasonic receiver receives the emitted wave signal and converts it into an electrical signal. Due to its small ranging range, it is primarily used in car reversing collision avoidance systems. Microwave radar ranging utilizes the reflection of electromagnetic waves by the target to detect and determine its position. Depending on the application of the microwave radar, the targets measured can be aircraft, missiles, vehicles, buildings, clouds, rain, etc. Laser ranging works on a similar principle to microwave radar ranging, with two specific ranging methods: continuous wave and pulse wave. This device uses the pulse wave method of laser ranging. 2.1 Laser Radar Ranging The structure of this device is shown in Figure 2. The device consists of a light-emitting unit, a light-receiving unit, a laser radar for calculating vehicle distance, a signal processing module, a display device, and a vehicle speed sensor. The laser lens illuminates a pulsed infrared laser beam forward, and the distance is detected by the light-receiving device using the reflected light from the rearview mirror of the car, as shown in Figure 3. Using a car rearview mirror, the detection distance exceeds 100m, and the maximum detection width is over 3.5m. Regarding the alarm range, through control circuitry, the left and right laser beams are set to have a detection range of over 315m and a width of 3.5m, while the central laser beam has a detection range of over 100m. This allows for earlier detection of vehicles entering traffic and triggering an alarm. It also suppresses alarms triggered by markers on curves, achieving optimal performance. The width control effectively controls the accuracy of the alarm. See Figure 4 (A, B). 2.2 Signal Processing and Control: The control section, a 32-bit embedded system, performs the following functions: calculates the vehicle speed and distance to the vehicle; and displays this information in real-time on an LCD (the display is mounted on the dashboard for distance display). Based on the comparison between the vehicle's current distance and the safe distance, an alarm sound or flashing alarm light is emitted. Article 80 of the Implementation Regulations of the Road Traffic Safety Law of the People's Republic of China stipulates that when a motor vehicle is traveling on a highway at a speed exceeding 100 km/h, it shall maintain a distance of at least 100 meters from the vehicle in front in the same lane. When the speed is below 100 km/h, the distance from the vehicle in front in the same lane may be appropriately shortened, but the minimum distance shall not be less than 50 meters. Relevant personnel from the traffic management department explained that when the speed of a motor vehicle is 60 km/h, the following distance should be at least 60 meters; when the speed is 80 km/h, the following distance should be at least 80 meters. Therefore, the safe distance depends on the specific speed. The mathematical model for inferring the degree of danger is: when V ≥ 100, S > 100; when 100 > V, S > Vt/1000 > 50; (the minimum distance shall not be less than 50 meters). S is the safe driving distance in meters; V is the vehicle speed in km/h; t is the speed per hour. Signal processing and control utilize a 16-bit Sunplus microcontroller to analyze signals from the vehicle speed sensor and lidar, and issue alarm signals. The specific implementation is shown in the following program: #include "SPCE061V004.HJ uli(); void Sound(int n); void Xianshi(float S); ChuanKOU(); // Data serialized from ARM; main() float v, S, v1, v2; int shisu = 200; * P_IOA_Dir = 0x0fff; // The lower 14 bits of IOA are used as external AD ports; * P_IOA_Data = 0; * P_IOB_Dir = 0x0000; // IOB0~16 are digital tube interfaces; * P_IOB_Data = 0; while (1) {v1 = ChuanKOU(); // The lower 16 bits of data serialized from ARM; v2 = ChuanKOU(); // The higher 16 bits of data serialized from ARM Bit; v = (v1/ 0xffff) * shisu; v = v + (v2/0xffff) * shisu S = Juli(); // Distance measurement subfunction Xianshi (S); // Display subfunction if (v >= 100 &S < 100) {Sound (0); // Voice alarm } if (v < 100 & (50 > S| v/ 1000 > S) ) {Sound (1); // Voice alarm } } } 2.3 Alarm Module The alarm module of this device consists of LEDs and speakers controlled by a Lingyang microcontroller. When the distance between vehicles reaches or exceeds the safe distance, the microcontroller sends a signal: the LEDs flash and a voice alarm sounds. Among them, there are 8 red LEDs; the speaker emits a voice alarm: "Attention!" or "Danger!". 3 Conclusion This research focuses on a vehicle-mounted ranging safety warning device for preventing rear-end collisions. It employs lidar ranging, utilizes ARM technology with powerful data processing capabilities for the control unit, and uses a Sunplus microcontroller for voice prompts and audible/visual alarms. This warning device is characterized by advanced technology, reliable performance, and a high performance-to-price ratio, making it practically valuable.