Grab Alarm Using arduino + LDR + piezo buzzer

This small project will teach you, how to make a simple Grab alarm using an LDR ( light dependent resistor).When you try to move your hand over the LDR, there is a loud alarm that goes on , and the alarm turns off as soon as you move your hand away from the LDR. The LDR works on the following principle " WHEN LIGHT FALLING ON THE LDR IS HIGH;RESISTANCE IS LOW ." and vice-versa. Basically for an LDR , light is inversely proportional to the Resistance.

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Grab Alarm Using arduino + LDR + piezo buzzer
  • LDR ( you can choose any variant ), these come in various sizes ,usually based on the size of the area on which the light falls.
  • Piezo buzzer (PCB MOUNT).
  • Resistor (220ohm /1kohm)
  • Connecting wires or Jumper cables
  • Arduino UNO R3
  • USB cable
  • Breadboard

    Step 2: Procedure

    Grab Alarm Using arduino + LDR + piezo buzzer

    1. Connect one terminal of the piezo buzzer to Digital pin 9(you can choose and PWM enabled pin) , and connect the other terminal to ground . Your buzzer connection is now complete.

    2. Now make the connections similar to that given in the picture

  • the black wire goes to ground
  • the green wire goes to pin A0 on the Arduino
  • the red wire goes to the 5v pin on the Arduino

    Step 3: Circuit diagram and Schematics

    Grab Alarm Using arduino + LDR + piezo buzzer
    Grab Alarm Using arduino + LDR + piezo buzzer

    Step 4: SOURCE CODE :

    Grab Alarm Using arduino + LDR + piezo buzzer
    int rcvpin=A0;int buzzpin=9; void setup() { pinMode(rcvpin,INPUT); pinMode(buzzpin,OUTPUT); buzz(200); buzz(200); buzz(200); delay(2000); Serial.begin(9600); }void loop() { int ldrval=analogRead(rcvpin); Serial.println(ldrval); if(ldrval>=900) { buzz(50); } } void buzz(unsigned char time) { analogWrite(buzzpin,170); delay(time); analogWrite(buzzpin,0); delay(time); }

    Step 5: DISCUSSIONS :

  • I have used ldrval variable to store the value being sent by the LRD connected to the arduino
  • The value is then printed on the serial monitor . This following part is very crucial .
  • After you have fully connected your circuit , you should upload your sketch to the arduino and then open the Serial monitor from the tools section on your arduino platform .
  • If your sketch is working properly then it should send back some values to your serial monitor .
  • Try to place your hand closer to the serial monitor and observe the readings changing .
  • In this manner you have to decide what your threshold value will be ; crossing which your buzzer will start.In my case ,this value was 900. Try to play around with this value , as this decides the sensitivity of the Alarm going on.
  • See the source code line 28 : you can also play around with the value . In my case i put it to 170 . You can use values ranging from 0-255 , where 0 represents off .



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