Vehicle inspection device design based on variable counting threshold (1)

With the increase of road speed and the rapid increase of the number of vehicles, the vehicle inspection device must have fast response time, accurate judgment ability and stable working state. Car inspection technology mainly includes: video [1], toroidal coil [2], digital microwave [2], laser and infrared. Although there are many types of detection technologies, there are still many shortcomings: on the one hand, the anti-interference ability is poor, and the product cost is relatively high; on the other hand, the detection response time is long, and it is difficult to detect the high-speed passing vehicle in time and accurately.

For the road environment and vehicle traffic conditions of conventional highways, the vehicle inspection device introduced in this paper adopts the toroidal coil detection technology. The technical principle is simple, the implementation cost is low, and the work is stable and reliable. In terms of signal analysis and processing, the ATmega16A microcontroller with stable performance is used [3]. The vehicle detection signal is directly analyzed and processed by the MCU. The detection response time of each channel is controlled within 2.5 ms. The detection result is indicated by the indicator light on the front panel of the vehicle inspection device, and the RS485 bus is used to send the detection to the host computer or other monitoring equipment. Result packet.

1 System working principle

1.1 Loop coil detection principle

The toroidal coil buried under the road surface is connected to the vehicle inspection device through the feeder, and the LC resonance circuit is formed with the capacitor and the triode on the vehicle inspection device, and the generated sinusoidal oscillation signal is arranged into a square wave signal and sent to the single chip microcomputer. When no vehicle passes, it can be considered that the inductance value formed by the toroidal coil is stable, so the resonant frequency of the LC resonant circuit is also unchanged, and the single-chip microcomputer receives a square wave of a fixed frequency, which is denoted as F1. When there is a passing through the buried toroidal coil, since the motor vehicle is a large metal body, the inductance generated by the buried coil will change, so that the frequency of the LC resonant circuit also changes, and the square wave frequency received by the single chip microcomputer is recorded as F1+ΔF; When the motor vehicle leaves the buried coil, the LC resonance frequency will return to F1, thereby realizing the change of the vehicle's passing frequency to the square wave frequency sent to the single chip microcomputer.

1.2 Working principle of variable counting threshold

For the counting mode using the fixed threshold [4], the main counter is given a fixed time counting time, and the detection signal is used as the counting clock, as shown in FIG.

[1] [2]