![](https://csdnimg.cn/release/download_crawler_static/88159376/bg4.jpg)
1.1 System design
The automobile security examination uses the ultrasonic
sensor. The ultrasonic sensor is composed by the ultrasonic
wave transmission circuit and the supersonic reception electric
circuit, in the automobile cab appropriate position, installs the
ultrasonic wave launch/receiver, as well as switch electric circuit
T1. When the automobile parks the vehicle owner person must
leave the automobile, with remote control closed switch T1, the
automobile alarm system sat garrisons the condition, around
the system use ultrasonic wave examination vehicle obstacle.
Launches the partial electric circuits likes chart 1 to show. When
its P1 mouth P1.1, P1.2 to the D trig , the P1.0 control ultrasonic
wave launch, are 0, the photo electricity coupler outputs the
TP1 end is 1, the permission ultrasonic wave launch,
launches/the receive ultrasonic wave in turn, the circulation
repeatedly carries on. Simultaneously the monolithic integrated
circuit interior counter starts to count. The steam distance
between vehicles obstacle distance is the time which sends out
through the sound navigation and ranging reflects spends
determines and carries on the computation. The reflection
signal causes the D trigger to produce interrupt request signal
INT1,simultaneously stops counting, reads takes counts the