上一次使用了有源蜂鳴器，只能發出固定的”滴滴“聲，當然不能滿足於此呀。使用無源蜂鳴器，只要輸出不同頻率的PWM波，即可發出不同的音符。
不同的音符組合起來就是一個曲子了。
改變PWM的音調，可以輸出Do re mi fa so la si do這樣的7個音符，還可以輸出不同音調的Do re mi fa so la si do。
在實例程序里面，我定義了低中高三個音階。音符的頻率則是mbed提供的。已經宏定義好了。
只要改變PWM的輸出周期，即可發出不同的音調（頻率是周期的倒數）。
為了方便起見，寫了一個音階類（Pitch），虛基類。里面有一個perform函數，參數是音符和持續時間。例如要發出Do這個聲音，持續0.5s，只要perform(1,0.5)就好。
還有一個Stop函數，停止響聲0.5s則stop（0.5），無參數則直接停止。后面的Low、Mid、High類則是派生類，實現了Pitch的虛函數。
程序里面包括：
1、發出低中高三個聲調的Do re mi fa so la si do音。
2、中音版的小星星。
3、低音版的小星星。
#include "mbed.h" #define NOTE_B0 31 #define NOTE_C1 33 #define NOTE_CS1 35 #define NOTE_D1 37 #define NOTE_DS1 39 #define NOTE_E1 41 #define NOTE_F1 44 #define NOTE_FS1 46 #define NOTE_G1 49 #define NOTE_GS1 52 #define NOTE_A1 55 #define NOTE_AS1 58 #define NOTE_B1 62 #define NOTE_C2 65 #define NOTE_CS2 69 #define NOTE_D2 73 #define NOTE_DS2 78 #define NOTE_E2 82 #define NOTE_F2 87 #define NOTE_FS2 93 #define NOTE_G2 98 #define NOTE_GS2 104 #define NOTE_A2 110 #define NOTE_AS2 117 #define NOTE_B2 123 #define NOTE_C3 131 #define NOTE_CS3 139 #define NOTE_D3 147 #define NOTE_DS3 156 #define NOTE_E3 165 #define NOTE_F3 175 #define NOTE_FS3 185 #define NOTE_G3 196 #define NOTE_GS3 208 #define NOTE_A3 220 #define NOTE_AS3 233 #define NOTE_B3 247 #define NOTE_C4 262 #define NOTE_CS4 277 #define NOTE_D4 294 #define NOTE_DS4 311 #define NOTE_E4 330 #define NOTE_F4 349 #define NOTE_FS4 370 #define NOTE_G4 392 #define NOTE_GS4 415 #define NOTE_A4 440 #define NOTE_AS4 466 #define NOTE_B4 494 #define NOTE_C5 523 #define NOTE_CS5 554 #define NOTE_D5 587 #define NOTE_DS5 622 #define NOTE_E5 659 #define NOTE_F5 698 #define NOTE_FS5 740 #define NOTE_G5 784 #define NOTE_GS5 831 #define NOTE_A5 880 #define NOTE_AS5 932 #define NOTE_B5 988 #define NOTE_C6 1047 #define NOTE_CS6 1109 #define NOTE_D6 1175 #define NOTE_DS6 1245 #define NOTE_E6 1319 #define NOTE_F6 1397 #define NOTE_FS6 1480 #define NOTE_G6 1568 #define NOTE_GS6 1661 #define NOTE_A6 1760 #define NOTE_AS6 1865 #define NOTE_B6 1976 #define NOTE_C7 2093 #define NOTE_CS7 2217 #define NOTE_D7 2349 #define NOTE_DS7 2489 #define NOTE_E7 2637 #define NOTE_F7 2794 #define NOTE_FS7 2960 #define NOTE_G7 3136 #define NOTE_GS7 3322 #define NOTE_A7 3520 #define NOTE_AS7 3729 #define NOTE_B7 3951 #define NOTE_C8 4186 #define NOTE_CS8 4435 #define NOTE_D8 4699 #define NOTE_DS8 4978 //7個音符組成了美妙的音樂 //低 Do re mi fa so la si do int melody[] = { NOTE_C4, NOTE_D4,NOTE_E4, NOTE_F4, NOTE_G4,NOTE_A4,NOTE_B4,NOTE_C5}; //中 Do re mi fa so la si do int melody2[] = { NOTE_C5, NOTE_D5,NOTE_E5, NOTE_F5, NOTE_G5,NOTE_A5,NOTE_B5,NOTE_C6}; //高 int melody3[] = { NOTE_C6, NOTE_D6,NOTE_E6, NOTE_F6, NOTE_G6,NOTE_A6,NOTE_B6,NOTE_C7}; //PWM輸出口 PwmOut m(PB_13); //音調類 class Pitch{ public: virtual void perfrom(int,double)=0; void stop(double time = 0){ if(time==0) m = 1; else{ m = 1; wait(time); }//end else }//end stop }; class Low:public Pitch{ public: void perfrom(int index,double time){ m.period_us(1000000/melody[index-1]); m.write(0.5); wait(time); } }; class Mid:public Pitch{ public: void perfrom(int index,double time){ m.period_us(1000000/melody2[index-1]); m.write(0.5); wait(time); } }; class Hig:public Pitch{ public: void perfrom(int index ,double time){ m.period_us(1000000/melody3[index-1]); m.write(0.5); wait(time); } }; int main() { /*試音 for (int thisNote = 0; thisNote < 8; thisNote++) { m.period_us(1000000/melody[thisNote]); m.write(0.5); wait(0.5); } for (int thisNote = 0; thisNote < 8; thisNote++) { m.period_us(1000000/melody2[thisNote]); m.write(0.5); wait(0.5); } for (int thisNote = 0; thisNote < 8; thisNote++) { m.period_us(1000000/melody3[thisNote]); m.write(0.5); wait(0.5); } m = 1; */ /*中音版 Mid mid; //11 55 66 5 mid.perfrom(1,0.5); mid.perfrom(1,0.5); mid.perfrom(5,0.5); mid.perfrom(5,0.5); mid.perfrom(6,0.5); mid.perfrom(6,0.5); mid.perfrom(5,0.8); mid.stop(0.2); //44 33 22 1 mid.perfrom(4,0.5); mid.perfrom(4,0.5); mid.perfrom(3,0.5); mid.perfrom(3,0.5); mid.perfrom(2,0.5); mid.perfrom(2,0.5); mid.perfrom(1,0.5); mid.stop(0.2); //55 44 33 2 mid.perfrom(5,0.5); mid.perfrom(5,0.5); mid.perfrom(4,0.5); mid.perfrom(4,0.5); mid.perfrom(3,0.5); mid.perfrom(3,0.5); mid.perfrom(2,0.5); mid.stop(0.2); //55 44 33 2 mid.perfrom(5,0.5); mid.perfrom(5,0.5); mid.perfrom(4,0.5); mid.perfrom(4,0.5); mid.perfrom(3,0.5); mid.perfrom(3,0.5); mid.perfrom(2,0.5); mid.stop(0.2); //11 55 66 5 mid.perfrom(1,0.5); mid.perfrom(1,0.5); mid.perfrom(5,0.5); mid.perfrom(5,0.5); mid.perfrom(6,0.5); mid.perfrom(6,0.5); mid.perfrom(5,0.5); mid.stop(0.2); //44 33 22 1 mid.perfrom(4,0.5); mid.perfrom(4,0.5); mid.perfrom(3,0.5); mid.perfrom(3,0.5); mid.perfrom(2,0.5); mid.perfrom(2,0.5); mid.perfrom(1,0.5); mid.stop(); */ //低音版 Low low; //11 55 66 5 low.perfrom(1,0.5); low.perfrom(1,0.5); low.perfrom(5,0.5); low.perfrom(5,0.5); low.perfrom(6,0.5); low.perfrom(6,0.5); low.perfrom(5,0.8); low.stop(0.2); //44 33 22 1 low.perfrom(4,0.5); low.perfrom(4,0.5); low.perfrom(3,0.5); low.perfrom(3,0.5); low.perfrom(2,0.5); low.perfrom(2,0.5); low.perfrom(1,0.5); low.stop(0.2); //55 44 33 2 low.perfrom(5,0.5); low.perfrom(5,0.5); low.perfrom(4,0.5); low.perfrom(4,0.5); low.perfrom(3,0.5); low.perfrom(3,0.5); low.perfrom(2,0.5); low.stop(0.2); //55 44 33 2 low.perfrom(5,0.5); low.perfrom(5,0.5); low.perfrom(4,0.5); low.perfrom(4,0.5); low.perfrom(3,0.5); low.perfrom(3,0.5); low.perfrom(2,0.5); low.stop(0.2); //11 55 66 5 low.perfrom(1,0.5); low.perfrom(1,0.5); low.perfrom(5,0.5); low.perfrom(5,0.5); low.perfrom(6,0.5); low.perfrom(6,0.5); low.perfrom(5,0.5); low.stop(0.2); //44 33 22 1 low.perfrom(4,0.5); low.perfrom(4,0.5); low.perfrom(3,0.5); low.perfrom(3,0.5); low.perfrom(2,0.5); low.perfrom(2,0.5); low.perfrom(1,0.5); low.stop(); }
蜂鳴器比較刺耳其實，聽久了還是很難受。
在代碼里面是不能調節音量的，要調低音量，加個電阻就好。最大的音量是無電阻+高電壓。
沒法錄音，所以還是上圖。
效果可以上秒拍聽一下：http://video.weibo.com/show?fid=1034:aee9c2288407e28eca7eb89d5ecc8a1d
