lesson_19.rst

Lesson 19 Sound Sensor

Introduction

Sound sensor is a component that receives sound waves and converts them into electrical signal. It detects the sound intensity in ambient environment like a microphone.

Required Components

• 1 * Raspberry Pi
• 1 * Breadboard
• 1 * PCF8591
• 1 * Sound sensor module
• 1 * 3-Pin anti-reverse cable
• Several Jumper wires

Experimental Principle

The microphone on the sensor module can convert audio signals into electrical signals (analog quantity), then convert analog quantity into digital quantity by PCF8591 and transfer them to MCU.

LM358 is a dual-channel operational amplifier. It contains two independent, high gain, and internally compensated amplifiers, but we will only use one of them in this experiment. The microphone transforms sound signals into electrical signals and then sends out the signals to pin 2 of LM358 and outputs them to pin 1 (that's, pin SIG of the module) via the external circuit. Then use PCF8591 to read analog values.

PCF8591 is an 8-bit resolution, 4-channel A/D，1-channel D/A conversion chip. We connect the output terminal (SIG) to AIN0 of PCF8591 so as to detect the strength of voice signal in a real-time manner.

The schematic diagram of the module is as shown below:

Experimental Procedures

Step 1: Build the circuit according to the following method.

Raspberry Pi	GPIO Extension Board	PCF8591 Module
SDA	SDA1	SDA
SCL	SCL1	SCL
3.3V	3V3	VCC
GND	GND	GND

Sound Sensor Module	GPIO Extension Board	PCF8591 Module
SIG	*	AIN0
VCC	3V3	VCC
GND	GND	GND

For C Users:

Step 2: Change directory.

cd /home/pi/SunFounder_SensorKit_for_RPi2/C/19_sound_sensor/

Step 3: Compile.

gcc sound_sensor.c -lwiringPi

Note

If it does not work after running, or there is an error prompt wiringPi.h: No such file or directory, please refer to install_wiringpi to install it.

Step 4: Run.

sudo ./a.out

Code

#include <stdio.h>
#include <wiringPi.h>
#include <pcf8591.h>

#define PCF       120

int main (void)
{
    int value;
    int count = 0;
    wiringPiSetup ();
    // Setup pcf8591 on base pin 120, and address 0x48
    pcf8591Setup (PCF, 0x48);
    while(1) // loop forever
    {
        value = analogRead  (PCF + 0);
        printf("value: %d\n", value);
        if (value < 80){
            printf("Voice In!! \n");
        }
        delay(100);
    }
    return 0;
}

For Python Users:

Step 2: Change directory.

cd /home/pi/SunFounder_SensorKit_for_RPi2/Python/

Step 3: Run.

sudo python3 19_sound_sensor.py

Code

#!/usr/bin/env python3
import PCF8591 as ADC
import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)

def setup():
    ADC.setup(0x48)

def loop():
    count = 0
    while True:
        voiceValue = ADC.read(0)
        if voiceValue:
            print ("Value:", voiceValue)
            if voiceValue < 50:
                print ("Voice In!! ", count)
                count += 1
            time.sleep(0.2)

if __name__ == '__main__':
    try:
        setup()
        loop()
    except KeyboardInterrupt: 
        pass    

Now, speak close to or blow to the microphone, and you can see "Voice In!!" printed on the screen.