Lesson 14 Quiz Buzzer System

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Introduction

In quiz shows, especially entertainment activities (e.g. competitive answering activities), organizers often apply a quiz buzzer system in order to accurately, fairly and visually determine the seat number of a responder. In this lesson, we will use some buttons, buzzers, and LEDs to make a quiz buzzer system.

Newly Added Components

Schematic Diagram

Button 2, 3 and 4 are answer buttons, and button 1 is the reset button. If button 2 is pressed first, the buzzer will beep, the corresponding LED will light up and all the other LEDs will go out. If you want to start another round, press button 1 to reset.

Build the Circuit

For C Language Users

Command

  1. Go to the folder of the code.

cd /home/pi/electronic-kit/for-raspberry-pi/c/Lesson_14_AnswerMachine

  1. Compile the code.

gcc 14_AnswerMachine.c -lwiringPi

  1. Run the executable file.

sudo ./a.out

Now, first press button 4 to get started. 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.

Code

1.<include <wiringPi.h>  
2.#include <stdio.h>  
3.  
4.#define BeepPin 0  
5.#define ResetBtnPin 1  
6.const int BtnPin[] = {2,3,4};  
7.const int LedPin[] = {21,22,23,24};  
8.  
9.void Alarm()  
10.{  
11.    for(int i=0;i<50;i++){  
12.    digitalWrite(BeepPin,HIGH); //the buzzer sound  
13.    delay(2); //delay 2ms  
14.    digitalWrite(BeepPin,LOW);  //without sound  
15.    delay(2);         
16.  }  
17.}  
18.  
19.int main(void){  
20.    if(wiringPiSetup() == -1){ //when initialize wiring failed, print message to screen  
21.        printf("setup wiringPi failed !");  
22.        return 1;   
23.    }  
24.      
25.     pinMode(BeepPin, OUTPUT);     
26.    for(int j=1;j<4;j++)  
27.    {  
28.        pinMode(LedPin[j], OUTPUT);  
29.        digitalWrite(LedPin[j],LOW);  
30.    }  
31.    pinMode(LedPin[0], OUTPUT);  
32.    digitalWrite(LedPin[0],HIGH);  
33.    for(int k;k<3;k++)  
34.    {  
35.        pinMode(BtnPin[k], INPUT);  
36.    }  
37.  
38.    int flag = 1;  
39.      
40.    while(1){  
41.        // if reset button is pressed  
42.        if(digitalRead(ResetBtnPin) == 1)  
43.        {  
44.                flag = 1;                
45.                digitalWrite(LedPin[0], HIGH);//Reset Led turns on  
46.                digitalWrite(LedPin[1],LOW);  
47.                digitalWrite(LedPin[2],LOW);  
48.                digitalWrite(LedPin[3],LOW);             
49.        }  
50.        if(flag==1)  
51.        {         
52.            //If the button1 press the first  
53.            if(digitalRead(BtnPin[0]) == 1)  
54.            {  
55.                    flag = 0;  
56.                    digitalWrite(LedPin[0],LOW);  
57.                    Alarm();  //buzzer sound  
58.                    digitalWrite(LedPin[1],HIGH);//turn the LED1 on only  
59.                    digitalWrite(LedPin[2],LOW);  
60.                    digitalWrite(LedPin[3],LOW);  
61.                    while(digitalRead(ResetBtnPin));            
62.            }  
63.             if(digitalRead(BtnPin[1]) == 1)  
64.            {          
65.                    flag = 0;  
66.                    digitalWrite(LedPin[0],LOW);  
67.                    Alarm();  //buzzer sound  
68.                    digitalWrite(LedPin[1],LOW);  
69.                    digitalWrite(LedPin[2],HIGH);//turn the LED2 on only  
70.                    digitalWrite(LedPin[3],LOW);  
71.                    while(digitalRead(ResetBtnPin));               
72.            }  
73.             if(digitalRead(BtnPin[2]) == 1)  
74.            {                                
75.                    flag = 0;  
76.                    digitalWrite(LedPin[0],LOW);  
77.                    Alarm();  //buzzer sound  
78.                    digitalWrite(LedPin[1],LOW);  
79.                    digitalWrite(LedPin[2],LOW);  
80.                    digitalWrite(LedPin[3],HIGH);//turn the LED3 on only  
81.                    while(digitalRead(ResetBtnPin));                  
82.            }            
83.        }         
84.    }  
85.    return 0;  
86.}  

Code Explanation

void Alarm()
{
for(int i=0;i<50;i++){
digitalWrite(BeepPin,HIGH); //the buzzer sound
delay(2);
digitalWrite(BeepPin,LOW); //without sound
delay(2);
}
}

Define a function to control the buzzer. The buzzer rings when this function is called in the main function.

int flag = 1;

Define a flag to judge whether the answer device is in the state of answering. When flag = 0, it indicates that someone is currently scrambling, and others cannot continue to answer first; when flag = 1, it means that the reset button has been pressed, and a new round of answer rush can be conducted.

if(digitalRead(ResetBtnPin) == 1)
{
flag = 1;
digitalWrite(LedPin[0], HIGH);//Reset Led turns on
digitalWrite(LedPin[1],LOW);
digitalWrite(LedPin[2],LOW);
digitalWrite(LedPin[3],LOW);
}

If the reset button is detected to have been pressed, it means that the answer begins. Now set flag to 1 and let the referee LED light up, the rest of the LED lights out.

if(digitalRead(BtnPin[0]) == 1)
{
flag = 0;
digitalWrite(LedPin[0],LOW);
Alarm(); //buzzer sound
digitalWrite(LedPin[1],HIGH);//turn the LED1 on only
digitalWrite(LedPin[2],LOW);
digitalWrite(LedPin[3],LOW);
while(digitalRead(ResetBtnPin));
}

In the process of quick answering, if the first button is recognized to have been pressed, the flag is set to 0, and then no other buttons are detected. At this time, the buzzer alarms, indicating that someone has successfully responsed, and the corresponding LED lights up. The identification codes of the remaining buttons are explained as above.

while(digitalRead(ResetBtnPin));

Having executed the instruction of successful quick answer, it enters the loop to judge whether the button reset is pressed. Here, if the button reset is pressed, then the next round of quickfire answering begins.

For Python Language Users

Command

  1. Go to the folder of the code.

cd /home/pi/electronic-kit/for-raspberry-pi/python

  1. Run the code.

sudo python3 14_AnswerMachine.py

Now, first press button 4 to get started. 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.

Code

1.import RPi.GPIO as GPIO  
2.import time  
3.  
4.BeepPin = 17  
5.ResetBtnPin = 18  
6.BtnPin =(27,22,23)  
7.LedPin =(5,6,13,19)  
8.  
9.def setup():  
10.    GPIO.setmode(GPIO.BCM)  
11.    GPIO.setup(BeepPin, GPIO.OUT, initial=GPIO.LOW)  
12.    GPIO.setup(ResetBtnPin, GPIO.IN)  
13.    GPIO.setup(LedPin[0], GPIO.OUT, initial=GPIO.HIGH)  
14.    for i in range(1,4):  
15.        GPIO.setup(LedPin[i], GPIO.OUT, initial=GPIO.LOW)  
16.    for i in range(0,3):  
17.        GPIO.setup(BtnPin[i], GPIO.IN)  
18.  
19.def Alarm():  
20.    for i in range(0,50):  
21.        GPIO.output(BeepPin,GPIO.HIGH)  
22.        time.sleep(0.003)  
23.        GPIO.output(BeepPin,GPIO.LOW)  
24.        time.sleep(0.003)  
25.  
26.def loop():  
27.    flag = 1  
28.    while True:  
29.        if GPIO.input(ResetBtnPin) == 1:  
30.            flag = 1  
31.            GPIO.output(LedPin[0],GPIO.HIGH)  
32.            GPIO.output(LedPin[1],GPIO.LOW)  
33.            GPIO.output(LedPin[2],GPIO.LOW)  
34.            GPIO.output(LedPin[3],GPIO.LOW)  
35.        if flag == 1:  
36.            if GPIO.input(BtnPin[0]) == 1:  
37.                flag = 0  
38.                GPIO.output(LedPin[0],GPIO.LOW)  
39.                Alarm()  
40.                GPIO.output(LedPin[1],GPIO.HIGH)  
41.                GPIO.output(LedPin[2],GPIO.LOW)  
42.                GPIO.output(LedPin[3],GPIO.LOW)  
43.            elif GPIO.input(BtnPin[1]) == 1:  
44.                flag = 0  
45.                GPIO.output(LedPin[0],GPIO.LOW)  
46.                Alarm()  
47.                GPIO.output(LedPin[1],GPIO.LOW)  
48.                GPIO.output(LedPin[2],GPIO.HIGH)  
49.                GPIO.output(LedPin[3],GPIO.LOW)  
50.            elif GPIO.input(BtnPin[2]) == 1:  
51.                flag = 0  
52.                GPIO.output(LedPin[0],GPIO.LOW)  
53.                Alarm()  
54.                GPIO.output(LedPin[1],GPIO.LOW)  
55.                GPIO.output(LedPin[2],GPIO.LOW)  
56.                GPIO.output(LedPin[3],GPIO.HIGH)  
57.  
58.def destroy():  
59.    # Turn off buzzer  
60.    GPIO.output(BeepPin, GPIO.LOW)  
61.    GPIO.output(LedPin[0],GPIO.LOW)  
62.    GPIO.output(LedPin[1],GPIO.LOW)  
63.    GPIO.output(LedPin[2],GPIO.LOW)  
64.    GPIO.output(LedPin[3],GPIO.HIGH)  
65.    # Release resource  
66.    GPIO.cleanup()      
67.  
68.# If run this script directly, do:  
69.if __name__ == '__main__':  
70.    setup()  
71.    try:  
72.        loop()  
73.    # When 'Ctrl+C' is pressed, the child program   
74.    # destroy() will be  executed.  
75.    except KeyboardInterrupt:  
76.        destroy() 

Code Explanation

def Alarm():
for i in range(0,50):
GPIO.output(BeepPin,GPIO.HIGH)
time.sleep(0.003)
GPIO.output(BeepPin,GPIO.LOW)
time.sleep(0.003)

Define a function to control the buzzer. The buzzer rings when this function is called in the function main.

flag = 1;

Define a flag bit to judge whether the responder is in the state of answering. When flag = 0, it indicates that someone is currently scrambling, and others cannot continue to answer first; when flag = 1, it means that the reset button has been pressed, and a new round of answer rush can be conducted.

if GPIO.input(ResetBtnPin) == 1:
flag = 1
GPIO.output(LedPin[0],GPIO.HIGH)
GPIO.output(LedPin[1],GPIO.LOW)
GPIO.output(LedPin[2],GPIO.LOW)
GPIO.output(LedPin[3],GPIO.LOW)

If the recognition that reset button has been pressed is done, it means that answer begins. Now, set flag to 1, and let the referee LED light up, other LEDs light out.

if GPIO.input(BtnPin[0]) == 1:
flag = 0
GPIO.output(LedPin[0],GPIO.LOW)
Alarm()
GPIO.output(LedPin[1],GPIO.HIGH)
GPIO.output(LedPin[2],GPIO.LOW)
GPIO.output(LedPin[3],GPIO.LOW)

In the process of quick answering, if the first button is recognized to have been pressed, the flag is set to 0, and then no other buttons are detected. At this time, the buzzer alarms, indicating that there is a successful response, and the corresponding LED lights up. The identification codes of the remaining buttons are explained as above.