How to make sound alert with ultrasonic sensor

In this post you will know  how  to build a sound alarm with ultrasonic sensor. You can use this system in many places. For example: Sound guide, (to guide someone to certain direction when he/she comes front of the sensor) to make yourself aware of something or someone and many more.

The sketch

#include <SoftwareSerial.h>
#define ARDUINO_RX 5 //should connect to TX of the Serial MP3 Player module
#define ARDUINO_TX 6 //connect to RX of the module
SoftwareSerial mySerial(ARDUINO_RX, ARDUINO_TX);
static int8_t Send_buf[8] = {0} ;

#define CMD_SEL_DEV 0X09
#define DEV_TF 0X02
#define CMD_PLAY_W_VOL 0X22

int trigPin1 = 9;
int echoPin1 = 8;

void setup()
  pinMode(trigPin1, OUTPUT);
  pinMode(echoPin1, INPUT);
      delay(500);//Wait chip initialization is complete
        sendCommand(CMD_SEL_DEV, DEV_TF);//select the TF card 
      delay(200);//wait for 200ms

void loop() {
 int duration1, distance1;
  digitalWrite (trigPin1, HIGH);
  delayMicroseconds (10);
  digitalWrite (trigPin1, LOW);
  duration1 = pulseIn (echoPin1, HIGH);
  distance1 = (duration1/2) / 29.1;

      Serial.print("1st Sensor: ");
      Serial.print("cm  ");

  if (distance1 < 40) {  // Change the number for long or short distances.
 sendCommand(CMD_PLAY_W_VOL, 0X1E001);//play the second song with volume 30 class
  } else {
// nothing

void sendCommand(int8_t command, int16_t dat)
  Send_buf[0] = 0x7e; //starting byte
  Send_buf[1] = 0xff; //version
  Send_buf[2] = 0x06; //the number of bytes of the command without starting byte and ending byte
  Send_buf[3] = command; //
  Send_buf[4] = 0x00;//0x00 = no feedback, 0x01 = feedback
  Send_buf[5] = (int8_t)(dat >> 8);//datah
  Send_buf[6] = (int8_t)(dat); //datal
  Send_buf[7] = 0xef; //ending byte
  for(uint8_t i=0; i<8; i++)//
    mySerial.write(Send_buf[i]) ;


What do you need:
1x Arduino board
1x Ultrasonic Sensor
1x Serial MP3 player
1x Loud speaker
1x SD card with a sound track in (Make sure you name the sound track 001)
And Few jumper wires.

Note: If you need extra help to set the sound please see this post.

Watch the video to see the sketch in action


  1. shared coding for two ultrasonic sensors

    1. shared coding for two ultrasonic sensors.. help me

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