树莓派 超声波测距

超声波模块工作原理：

通过原理图，我们首先要让Trig工作至少10us发出超声波，根据初中物理知识，dis = v（声）* t / 2 即可知距离

在库中有一个timeval的结构体：

struct timeval {
	time_t      tv_sec;     /* seconds */
    suseconds_t tv_usec;    /* microseconds */
};

实现代码：

#include <stdio.h>
#include <sys/time.h>
#include <wiringPi.h>
#define Trig 4
#define Echo 5

void Init(){
    pinMode(Trig,OUTPUT);
    pinMode(Echo,INPUT);
}
float Distance(){
    struct timeval start_time,end_time;
    long start,end;
    float dis;

    digitalWrite(Trig,LOW);
    delayMicroseconds(2);

    digitalWrite(Trig,HIGH);
    delayMicroseconds(10);
    digitalWrite(Trig,LOW);

    while(digitalRead(Echo) != HIGH);
    gettimeofday(&start_time,NULL);

    while(digitalRead(Echo) != LOW);
    gettimeofday(&end_time,NULL);

    start = start_time.tv_sec * 1000000 + start_time.tv_usec;
    end = end_time.tv_sec * 1000000 + end_time.tv_usec;
    dis = (float)(end - start) / 1000000 * 34000 / 2;

    return dis;
}

int main(){
    if(wiringPiSetup() == -1){
        printf("WiringPi starts failure!\n");
        return -1;
    }
    Init();
    while(1){
        printf("Distance = %.2fcm\n",Distance());
        delay(500);
    }
    return 0;
}

运行结果：
用手遮挡和不用手遮挡的测距