🔆 Project Title: Automatic Night Lamp using LDR and Arduino Nano

🔍 Project Overview:

This project automatically turns ON an LED when it is dark and OFF when there is light. It uses a Light Dependent Resistor (LDR) to detect the surrounding brightness and an Arduino Nano to control the LED based on the sensor’s readings. It’s a simple and practical automation system often used in night lamps and street lights.

⚙️ Circuit Connection Table

Component	Pin 1 Connection	Pin 2 Connection	Notes / Description
Arduino Nano	5V pin → Breadboard + (red line)	GND pin → Breadboard – (blue line)	Provides power and ground rails
LDR	One leg → Breadboard + (5V)	Second leg → Node X (junction point)	LDR detects light level
10kΩ Resistor	One leg → Node X (same as LDR 2nd leg)	Other leg → Breadboard – (GND)	Forms voltage divider with LDR
Jumper wire	Node X → A0 pin on Nano	—	Sends analog voltage from divider to Arduino
LED	Anode (+ longer leg) → One end of 220Ω resistor	Cathode (– shorter leg) → Breadboard – (GND)	LED lights up in dark
220Ω Resistor	One end → LED anode (+)	Other end → D3 pin on Nano	Limits current to LED
Power	Breadboard + → Arduino 5V	Breadboard – → Arduino GND	Common power connections

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🔁 Circuit Summary

• LDR + 10kΩ resistor form a voltage divider between 5V and GND.
• The junction (Node X) sends varying voltage to A0 (light intensity reading).
• Arduino checks this value:
  • If it’s dark (high reading) → turns ON LED at D3.
  • If it’s bright (low reading) → turns OFF LED.

Nano Pin	LDR Module Pin
5V	VCC
GND	GND
A0	AO
—	(DO not used)

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💡 Now add the LED part

Component	Connection 1	Connection 2	Notes
LED (any color)	Anode (+ longer leg) → One end of 220Ω resistor	Cathode (– shorter leg) → GND	Resistor limits current
220Ω Resistor	Other end → D3 pin on Arduino Nano	—	D3 will control the LED ON/OFF

So in simple words:

Nano D3 ----> 220Ω resistor ----> LED anode (+)
LED cathode (–) ----> GND

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⚙️ Final Arduino Nano Wiring Summary

Arduino Nano Pin	Connects To	Component / Function
5V	LDR Module VCC	Power to sensor
GND	LDR Module GND & LED cathode (–)	Common ground
A0	LDR Module AO	Reads light level
D3	220Ω resistor → LED anode (+)	Controls LED output

🌙 Automatic Night Lamp using LDR Sensor Module + LED

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Circuit

💾 Complete Code

const int LIGHT_SENSOR_PIN = A0; // The Arduino Nano pin connected to light sensor's  pin
const int LED_PIN          = 2;  // The Arduino Nano pin connected to LED's pin
const int ANALOG_THRESHOLD = 500;

int analog_value;

void setup() {
  pinMode(LED_PIN, OUTPUT); // set arduino pin to output mode
}

void loop() {
  analog_value = analogRead(LIGHT_SENSOR_PIN); // read the input on analog pin

  if(analog_value < ANALOG_THRESHOLD)
    digitalWrite(LED_PIN, HIGH); // turn on LED
  else
    digitalWrite(LED_PIN, LOW);  // turn off LED
}

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⚙️ How to Test

1. Upload the code to your Arduino Nano.
2. Open Serial Monitor (Tools → Serial Monitor) and set baud = 9600.
3. Note the readings in bright light and dark (cover the LDR).
4. Adjust the line int threshold = 500; → Increase the number if your LED turns on too early,
   → Decrease it if LED doesn’t turn on soon enough.

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✅ Expected Behavior

Light Condition	LDR Value (approx)	LED State
Bright Light	200–400	OFF
Dim / Dark	600–900	ON