using wiringPi to implement ultrasonic function

有關於wiringPi 的安裝和執行  請參考這篇   wiringPi

然後我發覺我超音波做不出來的原因是因為我理解錯誤....

參考timing diagram

重點是要去數  第三列的pulse為高電位的時間......


int ultrasonic_read(_pin){
        unsigned int  start_time,end_time,duraction;
        pinMode (_pin, OUTPUT) ;
        digitalWrite (_pin, LOW) ;
        delayMicroseconds(3);
        digitalWrite (_pin, HIGH) ;
        delayMicroseconds(11);
        digitalWrite (_pin, LOW);
        pinMode (_pin, INPUT) ;
        while(digitalRead(_pin)==LOW)
            delayMicroseconds(1);
        start_time = micros();
        while(digitalRead(_pin)==HIGH)
            delayMicroseconds(1);
        end_time = micros();
        if(start_time > end_time)
           duraction = (unsigned int)4294967295 - end_time + start_time;
        else
           duraction = end_time - start_time;
        return (0.17 * duraction);
}

把跑出來的資料plot 出來....結果就像下圖一樣