File content as of revision 1:3778bb7e3cf9:

#include "mbed.h"
#define SLIT_NUM 70
#define COUNT_NUM 10

Timer timer;
PwmOut pwm(p21);
InterruptIn Photo_int(p30);

int counter = 0;
int Cadence = 0;
int beforetime = 0;
int temp_time = 0;

double calcPulse(int deg)
{
    return (0.00093+(deg/180.0)*(0.00235-0.00077));
}

void servo(int d)
{
    if(d < 70)
        pwm.pulsewidth_us(0);
    if(d > 110)
        pwm.pulsewidth_us(180);
    else
        pwm.pulsewidth_us((d - 70) * (180 / 40));


}
        void Photo() {
        counter++;
    }

    int main() {
        Photo_int.fall(Photo);
        timer.start();
        while(1) {
            if(counter >= COUNT_NUM) {
                temp_time = timer.read_ms();
                Cadence =  (60 / ((SLIT_NUM / COUNT_NUM) * (temp_time) - beforetime)) * COUNT_NUM;
                beforetime = temp_time;
                counter = 0;

            }
                 servo(Cadence);
        }
   

    }