LDR Light Sensor Raspberry Pi

🟦 1. Introduction

An LDR (Light Dependent Resistor) is a sensor used to detect light intensity. Its resistance changes based on the amount of light falling on it. This makes it useful for automatic lighting and smart control systems.

🟦 2. Components

Raspberry Pi
LDR Sensor Module
LED
220Ω Resistor
Breadboard
Jumper Wires

🟦 3. Circuit and connections

Raspberry Pi Pinout Diagram

LDR Diagram

🔌 Connections:

VCC → 3.3V (Pin 1)
GND → GND (Pin 6)
DO → GPIO17 (Pin 11)
LED + → GPIO18 (Pin 12)
LED – → GND (via 220Ω resistor)

🟦 4. Detailed Step By Step Circuit working

LDR senses light intensity
In bright light → resistance decreases
In darkness → resistance increases
Sensor module converts this to digital signal
Raspberry Pi reads signal from GPIO17
In darkness → LED turns ON
In light → LED turns OFF

🟦 5. Libraries to be included


import RPi.GPIO as GPIO
import time

🟦 6. Code


import RPi.GPIO as GPIO
import time

ldr = 17
led = 18

GPIO.setmode(GPIO.BCM)
GPIO.setup(ldr, GPIO.IN)
GPIO.setup(led, GPIO.OUT)

while True:
    if GPIO.input(ldr) == 0:  # Dark condition
        GPIO.output(led, True)
        print("Dark - LED ON")
    else:
        GPIO.output(led, False)
        print("Light - LED OFF")
    time.sleep(0.1)

🟦 7. Detailed Step By Step Code working

Import GPIO and time libraries
Define LDR pin as GPIO17
Define LED pin as GPIO18
Set GPIO mode to BCM
Set LDR as input
Set LED as output
Read LDR sensor value
If LOW → dark detected → LED ON
Else → LED OFF
Add delay for smooth operation

🟦 8. Tips

Adjust sensitivity using onboard potentiometer
Avoid direct shadow blocking
Use proper resistor for LED protection
Place sensor in open light area

🟦 9. Uses

Automatic street lights
Smart home lighting
Light intensity monitoring
Energy saving systems

🟦 10. Conclusion

The LDR sensor is a simple and effective way to detect light levels. This project helps in building automatic lighting systems using Raspberry Pi.

Basic Electronics for Beginners