Introduction

Have you ever seen a security system that detects an intruder without even touching them? In this exciting STEM experiment, we build a Smart Shadow Detector using the components from the Plzpapa Robotic Kit. This project teaches students how electronic eyes (sensors) can detect movement by monitoring changes in light intensity.

Function: How It Works

The Shadow Detector acts as an invisible tripwire. Here is the step-by-step technical breakdown:

• Light Monitoring: The system uses an LDR (Light Dependent Resistor) to constantly measure the brightness of the room.
• Shadow Logic: We have calibrated the sensitivity threshold to a value of 300.
  • Normal State: When light falls on the sensor, the reading stays below 300. The system remains silent.
  • Active State: As soon as an object (like a hand or a person) passes over the sensor, it casts a shadow. This causes the sensor reading to spike above 300.
• Instant Reaction: The Arduino immediately processes this change and activates the output modules: turning on Double LEDs and sounding an Alarm Buzzer.

Purpose & Educational Value

Why should kids build this project with their Plzpapa Robotic Kit?

• Understanding Automation: It demonstrates how machines make decisions based on environmental data (Light vs. Dark).
• Physics of Light: Students learn about light intensity and how shadows affect electrical resistance.
• Real-World Application: This same technology is used in bank security systems, automatic door counters, and conveyor belts in factories.

Key Features

• High Sensitivity: Calibrated at a precise threshold (300) to detect even faint shadows instantly.
• Dual-Mode Alert: Features both a Visual Alert (2 LEDs turning ON) and an Audio Alert (Buzzer beeping) for maximum impact.
• Touchless Technology: A completely contactless system that detects presence solely through light obstruction.
• Easy Assembly: Built using the beginner-friendly components found in the Plzpapa Robotic Kit.

Components

To build this Smart Shadow Detector Alarm with Plzpapa Robotic Kit, we used the following parts from the Plzpapa Basic Robotic Kit:

• Arduino Uno
• LDR Sensor (Shadow detect karne ke liye)
• 2 LEDs (Red ya jo bhi hon)
• Buzzer
• 220 Ohm Resistor (Blue wala) – LEDs ke liye.
• Wires & Breadboard 

Wiring (Taarein Jorna)

1. BreadBoard:

• [BreadBoard +] Connect with GND
• [BreadBoard -] Connect with A0

2. LDR Wiring

• Leg 1: Arduino [BreadBoard +]
• Leg 2: Arduino A0.

3.LEDs Connections:

• LED 1 Bari Taang (+): Arduino Pin 12.
• LED 2 Bari Taang (+): Arduino Pin 13.
• Dono LEDs ki Choti Taangein (-): Aapas mein mila lein -> Phir Blue Resistor -> Phir [BreadBoard +]

5 .Buzzer Connections

• Bari Taang (+): Arduino Pin 10.
• Choti Taang (-): BreadBoard +ive.

Code

int ldrPin = A0;
int buzzer = 10;
int led1 = 12;
int led2 = 13;

int lightValue = 0;

// Yahan hum ne value change kar di hai
int shadowPoint = 300; 

void setup() {
  pinMode(buzzer, OUTPUT);
  pinMode(led1, OUTPUT);
  pinMode(led2, OUTPUT);
  
  // Internal Resistor ON
  pinMode(ldrPin, INPUT_PULLUP);
  
  Serial.begin(9600);
}

void loop() {
  lightValue = analogRead(ldrPin);
  Serial.print("Current Light: ");
  Serial.println(lightValue);

  // LOGIC: Agar reading 300 se ZYADA hui (Saya para)
  if (lightValue > shadowPoint) {
    
    // SHADOW DETECTED!
    digitalWrite(led1, HIGH);
    digitalWrite(led2, HIGH);
    digitalWrite(buzzer, HIGH);
    
  } else {
    
    // NO SHADOW
    digitalWrite(led1, LOW);
    digitalWrite(led2, LOW);
    digitalWrite(buzzer, LOW);
  }
  
  delay(100);
}