Lesson 11 Doorbell

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Introduction

In this lesson, we will learn how to drive an active buzzer to build a simple doorbell.

Newly Added Components

Schematic Diagram

When the button is pressed, Pin13 is connected to the 5V power supply and reads out high level; therefore, the program responds to make Pin11 output the high level so as to energize the transistor, and the collector will output low level that means the buzzer rings. When pin11 outputs at low level the buzzer will be silent.

Build the Circuit

Note: Long pins of buzzer is the Anode and the short pin is Cathode.

For C Language Users

Command

Go to the folder of the code.

cd /home/pi/electronic-kit/for-raspberry-pi/c/Lesson_11_DoorBell

Compile the code.

gcc 11_DoorBell.c -lwiringPi

Run the executable file.

sudo ./a.out

When the button is pressed, the buzzer makes a sound to simulate a doorbell.

Code

1.#include <wiringPi.h>  
2.#include <stdio.h>  
3.  
4.#define BeepPin 0  
5.#define ButtonPin   2  
6.  
7.int main(void){  
8.    if(wiringPiSetup() == -1){ //when initialize wiring failed, print message to screen  
9.        printf("setup wiringPi failed !");  
10.        return 1;   
11.    }  
12.      
13.    pinMode(BeepPin, OUTPUT);     
14.    pinMode(ButtonPin, INPUT);  
15.    pullUpDnControl(ButtonPin, PUD_DOWN);  
16.  
17.    while(1){  
18.        // Indicate that button has pressed down  
19.        if(digitalRead(ButtonPin) == 1){  
20.            delay(10);  
21.            if(digitalRead(ButtonPin) == 1){  
22.            //beep on  
23.            printf("Buzzer on\n");  
24.            digitalWrite(BeepPin, HIGH);  
25.            delay(100);  
26.            }  
27.        }  
28.        else{  
29.            printf("Buzzer off\n");  
30.            //beep off  
31.            digitalWrite(BeepPin, LOW);  
32.            delay(100);  
33.        }         
34.    }  
35.    return 0;  
36.}

Code Explanation

delay(10);

Software removes button jitter. When the signal that the button is pressed is detected, a delay of 10ms is used to eliminate the possibility of false judgment. If both if conditions are met, confirm that the button is pressed, and then execute the program in if.

if(digitalRead(ButtonPin) == 1){
//beep on
printf(“Buzzer on\n”);
digitalWrite(BeepPin, HIGH);
delay(100);
}

If the button is recognized to be pressed, the BeepPin is at high level. The base pin(b pin) of the connected transistor inputs high level, while the collector pin(c pin) outputs low level. That is, the cathode of buzzer is at low level, and the anode is connected with a high level 5V. Then the buzzer rings.

else{
printf(“Buzzer off\n”);
//beep off
digitalWrite(BeepPin, LOW);
delay(100);
}

Otherwise, BeepPin is at low level, and the base pin(b pin) of the connected transistor inputs low level, then the collector pin(c pin) outputs high level; that is, the level at both ends of the buzzer is high, and the buzzer does not ring.

For Python Language Users

Command

Go to the folder of the code.

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

Run the code.

sudo python3 11_DoorBell.py

When the button is pressed, the buzzer makes a sound to simulate a doorbell.

Code

1.import RPi.GPIO as GPIO  
2.import time  
3.  
4.BeepPin = 17  
5.BtnPin = 27  
6.  
7.def setup():  
8.    GPIO.setmode(GPIO.BCM)  
9.    GPIO.setup(BtnPin, GPIO.IN)  
10.    GPIO.setup(BeepPin, GPIO.OUT, initial=GPIO.LOW)  
11.      
12.def main():  
13.    while True:  
14.        if GPIO.input(BtnPin) == 0:  
15.            #Buzzer off  
16.            print ('Buzzer Off')  
17.            GPIO.output(BeepPin, GPIO.LOW)  
18.            time.sleep(0.1)  
19.        if GPIO.input(BtnPin) == 1:  
20.            #Buzzer on  
21.            print ('Buzzer On')  
22.            GPIO.output(BeepPin, GPIO.HIGH)  
23.            time.sleep(0.1)  
24.  
25.def destroy():  
26.    # Turn off buzzer  
27.    GPIO.output(BeepPin, GPIO.LOW)  
28.    # Release resource  
29.    GPIO.cleanup()      
30.  
31.# If run this script directly, do:  
32.if __name__ == '__main__':  
33.    setup()  
34.    try:  
35.        main()  
36.    # When 'Ctrl+C' is pressed, the child program   
37.    # destroy() will be  executed.  
38.    except KeyboardInterrupt:  
39.        destroy()

Code Explanation

if GPIO.input(BtnPin) == 0:
Buzzer off
print (‘Buzzer Off’)
GPIO.output(BeepPin, GPIO.LOW)
time.sleep(0.1)

If it is judged that the button is not pressed, BeepPin is at low level, and the base pin(b pin) of the connected transistor inputs low level, then the collector pin(c pin) outputs high level; that is, when the level at both ends of the connected buzzer is high, the buzzer does not ring.

if GPIO.input(BtnPin) == 1:
Buzzer off
print (‘Buzzer On’)
GPIO.output(BeepPin, GPIO.HIGH)
time.sleep(0.1)