1. /**********************************
2.  * name:Building a Quiz Buzzer System
3.  * function: first press button 4 to start. If you press button 1 first, you will see the corresponding LED light up and the buzzer will beep. Then press button 4 again to reset before you press other buttons.
4.  **********************************/
5.  
6.  
7. #define button1 2  //the number of the button 1
8. #define button2 3  //button2 attach to
9. #define button3 4  //button3 attach to
10. #define button4 9  //button4 attach to
11. #define buzzerPin 5  //the buzzer attach to    
12. #define LED1 6  //LED 1attach to      
13. #define LED2 7  //LED2attach to    
14. #define LED3 8  //LED3 attach to
15. #define LED4 10  //LED4 attach to
16. #define uint8 unsigned char
17. uint8 flag = 0;  //used to indicate the state of button4 key
18. uint8 b1State,b2State,b3State,b4State = 0;
19.  
20. void setup()
21. {
22.   //initialize buzzer,LED1, LED2, LED3 and LED4 as output
23.   pinMode(buzzerPin, OUTPUT);    
24.   pinMode(LED1, OUTPUT);
25.   pinMode(LED2, OUTPUT);    
26.   pinMode(LED3, OUTPUT);
27.   pinMode(LED4, OUTPUT);
28.   //initialize button1,button2 andbutton3 as input,combined with pullup
29.   pinMode(button1, INPUT_PULLUP);
30.   pinMode(button2, INPUT_PULLUP);
31.   pinMode(button3, INPUT_PULLUP);    
32.   pinMode(button4, INPUT_PULLUP);
33.   //turn all the led off
34.   digitalWrite(LED1, LOW);
35.   digitalWrite(LED2, LOW);  
36.   digitalWrite(LED3, LOW);
37.   digitalWrite(LED4, LOW);
38. }
39. void loop()
40. {
41.   //turn all the led off
42.   digitalWrite(LED1, LOW);
43.   digitalWrite(LED2, LOW);  
44.   digitalWrite(LED3, LOW);  
45.   digitalWrite(LED4, LOW);
46.   //read the state of the button4
47.   b4State = digitalRead(button4);
48.   //when button4 pressed
49.   if(b4State == 0)
50.   {
51.     if(b4State == 0)  //confirm that the button4 is pressed
52.     {
53.       flag = 1;  //if so,flag is 1
54.       digitalWrite(LED4, HIGH);  //turn the host LED on
55.       delay(200);  
56.     }
57.   }
58.   if(1 == flag)
59.   {
60.     //read the state of the button of buttons
61.     b1State = digitalRead(button1);  
62.     b2State = digitalRead(button2);
63.     b3State = digitalRead(button3);
64.     //If the button1 press the first
65.     if(b1State == 0)
66.     {
67.       flag = 0;
68.       digitalWrite(LED4, LOW);
69.       Alarm();  //buzzer sound
70.       digitalWrite(LED1,HIGH);  //turn the LED1 on only
71.       digitalWrite(LED2,LOW);
72.       digitalWrite(LED3,LOW);
73.       while(digitalRead(button4));  //detect the button4,if pressed,out of the while loop
74.     }
75.     //If the button2 press the first
76.     if(b2State == 0)
77.     {
78.       flag = 0;
79.       digitalWrite(LED4, LOW);
80.       Alarm();
81.       digitalWrite(LED1,LOW);
82.       digitalWrite(LED2,HIGH);
83.       digitalWrite(LED3,LOW);
84.       while(digitalRead(button4));
85.     }
86.     //If the button3 press the first
87.     if(b3State == 0)
88.     {
89.       flag = 0;
90.       digitalWrite(LED4, LOW);
91.       Alarm();
92.       digitalWrite(LED1,LOW);
93.       digitalWrite(LED2,LOW);
94.       digitalWrite(LED3,HIGH);
95.       while(digitalRead(button4));
96.     }
97.   }
98. }
99. //buzzer sound
100. void Alarm()        
101. {
102.   for(int i=0;i<100;i++){
103.     digitalWrite(buzzerPin,HIGH); //the buzzer sound
104.     delay(2);
105.     digitalWrite(buzzerPin,LOW);  //without sound
106.     delay(2);                     //when delay time changed,the frequency changed
107.   }
108. }
109.  
110.