Simple implementation solution for laser rangefinder
Laser ranging has high angular resolution and strong anti-interference ability, which can avoid the multi-path effect and ground object interference problems caused by microwaves close to the ground, and has the advantages of light weight, compact structure, and convenient installation and adjustment. One of the ideal instruments. After the construction of the railway tunnel is completed, the surrounding rock has a slow change trend, and the range finder can be used to measure its convergence.
1.2 Project background/topic motivation
According to our research, the price of ordinary handheld laser rangefinders in the market is about 1,000 yuan, and other communication interfaces such as serial ports are more than 2,000 yuan, and the functions are single and the interface is simple. Therefore, we use the AVR128 processor to construct a new type of laser ranging detection system, which has multi-function, high precision, automation and price advantages, and is applied to the monitoring of the surrounding rock convergence of railway tunnels.
2. Demand analysis
2.1 Functional Requirements
The designed range finder can measure the convergence of railway tunnels around the clock, and can save the data to SD card and transmit it to the monitoring center.
2.2 Performance requirements
The designed rangefinder, the angle is above 0.1mm, the module is stable and reliable, etc.
3. Scheme design
3.1 Principle of system function realization
Taking advantage of the characteristics of extremely short duration of laser pulse and high instantaneous power, even if there is no cooperative target, distance measurement can be performed by receiving the diffuse reflection signal of the measured target. The principle of pulsed laser ranging is similar to radar ranging. A pulsed laser is used to transmit a single laser pulse or laser pulse train to the target, and the counter measures the round-trip time of the laser pulse reaching the target and returning from the target to the receiver, thereby calculating the target's distance. The principle of pulse laser ranging is shown in Figure 1, and the ranging formula is: d=ct/2. Among them, d is the measurement distance, c is the speed of light, and t is the round-trip time of the ranging signal.
3.2 Hardware platform selection and resource allocation
Hardware platform selection: AVR XMEGA-A1 Xplained evaluation kit is based on 8-bit ATMEGA128 chip.
Use on-board resources: SPI interface, temperature sensor, light sensor, language speaker, serial port module.
3.3 System Software Architecture
The system first collects three important information: distance position, temperature and humidity, and external light intensity. Calculate and send according to the corresponding data to eliminate the influence of temperature and external light intensity on the spot position. When the distance position exceeds the set threshold, an alarm sound is sounded using the on-board speaker. The collected data is transmitted to the monitoring center by SD card data storage, LCD liquid crystal display and serial port.
