File content as of revision 0:41dfb0b1f108:

#include "mbed.h"
#define pwm_period_us 500
//#define pwm_pulsewidth_us 400
//實驗說明:利用鍵盤+-符號來控制馬達速度
PwmOut pwm_1(D9);
PwmOut pwm_2(D10);
PwmOut pwm_3(D11);
float pwm = 0.5;
DigitalIn button(USER_BUTTON);
int main()
{
    char a;
    pwm_1.period_us(pwm_period_us);
    pwm_2.period_us(pwm_period_us);
    pwm_3.period_us(pwm_period_us);

    pwm_1.write(0.5);
    pwm_2.write(0.5);
    pwm_3.write(0.5);
    printf("PWM all RESET to %.1f %%\n", pwm_1.read() * 100);

    while(1) {
        scanf("%c",&a);
        switch (a) {
            case '+':
                pwm += 0.05;
                pwm_1.write(pwm);
                pwm_2.write(pwm);
                pwm_3.write(pwm);
                printf("%c ; PWM all set to %.1f %%\n", a, pwm_1.read() * 100);
                break;
            case '-':
                pwm -= 0.05;
                pwm_1.write(pwm);
                pwm_2.write(pwm);
                pwm_3.write(pwm);
                printf("%c ; PWM all set to %.1f %%\n", a, pwm_1.read() * 100);
                break;
            /*case '3':
                pwm_3.write(pwm);
                printf("%c ; pwm_3 set to %.1f %%\n", a, pwm_3.read() * 100);
                break;
                
                case '0':
                    pwm_1.write(0.5);
                    pwm_2.write(0.5);
                    pwm_3.write(0.5);
                    printf("%c ; pwm all reset to %.1f %%\n", a, pwm_1.read() * 100);
                    break;
                */
            default:
                pwm_1.write(0.5);
                pwm_2.write(0.5);
                pwm_3.write(0.5);
                printf("PWM all RESET to %.1f %%\n", pwm_1.read() * 100);
                break;
        }
    }
}