☀️ Photoresistor (Light Sensor)

📌 Description

A photoresistor (also called an LDR – Light Dependent Resistor) changes its resistance depending on how much light shines on it. More light → lower resistance → higher voltage reading. Less light → higher resistance → lower voltage reading.

🎯 Use

In our projects, the photoresistor is used to:

• Measure light intensity.
• Detect day/night conditions.
• Control brightness‑based actions (like turning on LEDs when it’s dark).

👉 Think of the photoresistor as the robot’s eyes for brightness — it tells the robot how much light is around.

Module parameters

Pin name	Description
G	GND (Power Input Negative)
V	VCC (Power Input Cathode)
S	Analog signal pins

• Supply voltage: 3.3V/5V
• Connection: PH2.0 terminal wire
• Installation method: double screw fixing

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🖥️ Corrected Code Explanation

import machine
import time

adc39 = machine.ADC(machine.Pin(39))          # Photoresistor connected to pin 39
adc39.atten(machine.ADC.ATTN_11DB)            # Set attenuation for wider voltage range
adc39.width(machine.ADC.WIDTH_12BIT)          # 12-bit resolution (0–4095)

while True:
    light_intensity = adc39.read()            # Read light level
    print('Light Intensity: ', light_intensity)
    time.sleep(0.5)                           # Wait half a second

Step by Step

1. adc39 = machine.ADC(machine.Pin(39)) → Reads the analog signal from the photoresistor.
2. atten and width → Configure the ADC for accurate readings (0–4095).
3. while True: → Loop that repeats forever.
4. light_intensity = adc39.read() → Reads the brightness level.
5. print(...) → Shows the light intensity value.
6. time.sleep(0.5) → Adds a short delay between readings.

👉 Together, this program prints the light intensity every half second.

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✅ Conclusion of the Test

• If the printed values increase when exposed to bright light and decrease in darkness, the program is working correctly.
• This test shows how the robot can sense light levels and react to brightness changes.
• Later, the photoresistor could be used to automatically turn on lights at night, adjust screen brightness, or trigger alarms when light changes suddenly.