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Reading a Photoresistor — SIK Circuit 6
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17. uNdasa 2026FI
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Reading a Photoresistor — SIK Circuit 6

Use a photoresistor (light sensor) to control LED brightness. Learn about voltage dividers, analog input, and the map() function for sensor-to-output conversion.

Imiyalelo

1

Parts & Introduction

A photoresistor (or LDR — Light Dependent Resistor) changes resistance based on light levels. Combined with a fixed resistor, it forms a voltage divider that the Arduino can read as an analog value. You'll use this to control LED brightness automatically.

Parts Needed

  • 1x Arduino Uno + USB cable
  • 1x Breadboard
  • 1x Photoresistor
  • 1x LED (any color)
  • 1x 330Ω Resistor
  • 1x 10KΩ Resistor (for voltage divider)
  • 6x Jumper Wires

Izinto zokwakha zalesi sinyathelo:

SparkFun Inventor's Kit - V3.2SparkFun Inventor's Kit - V3.21 ikhithi

Amathuluzi adingekayo:

Computer with Arduino IDEComputer with Arduino IDE
2

Hardware Hookup

Wiring Instructions

  1. Connect one side of the photoresistor to 5V.
  2. Connect the other side to Analog Pin A0.
  3. Connect a 10K resistor from Analog Pin A0 to GND (this completes the voltage divider).
  4. Connect the LED positive leg to Digital Pin 9 (PWM-capable).
  5. Connect the LED negative leg through a 330Ω resistor to GND.

The voltage divider produces a voltage proportional to light level, which the Arduino reads as 0-1023.

Izinto zokwakha zalesi sinyathelo:

BreadboardBreadboard1 ucezu
Jumper WiresJumper Wires5 izicucu
3

Arduino Code

Open the Arduino IDE and upload the following sketch to your Arduino board.

photoresistor.inoarduino
/*
SparkFun Inventor's Kit
Example sketch 06 — PHOTORESISTOR

Use a photoresistor (light sensor) to control LED brightness.

Hardware connections:
  Photoresistor: one side to 5V, other side to analog pin 0
  10K resistor between analog pin 0 and GND
  LED: positive to digital pin 9 (PWM), negative through 330 ohm to GND

This code is completely free for any use.
*/

const int sensorPin = 0;
const int ledPin = 9;

int lightLevel, high = 0, low = 1023;

void setup()
{
  pinMode(ledPin, OUTPUT);
}

void loop()
{
  lightLevel = analogRead(sensorPin);

  manualTune();

  //autoTune();

  analogWrite(ledPin, lightLevel);
}

void manualTune()
{
  lightLevel = map(lightLevel, 0, 1023, 0, 255);
  lightLevel = constrain(lightLevel, 0, 255);
}

void autoTune()
{
  if (lightLevel < low)
  {
    low = lightLevel;
  }
  if (lightLevel > high)
  {
    high = lightLevel;
  }

  lightLevel = map(lightLevel, low+30, high-30, 0, 255);
  lightLevel = constrain(lightLevel, 0, 255);
}

Izinto zokwakha zalesi sinyathelo:

Arduino Uno R3Arduino Uno R31 ucezu

Amathuluzi adingekayo:

Computer with Arduino IDEComputer with Arduino IDE
4

Test & Experiment

What You Should See

The LED brightness changes based on ambient light. Cover the photoresistor to dim or brighten the LED (depending on orientation).

Troubleshooting

  • LED stays dark: Check LED polarity. Also verify the photoresistor is in the circuit correctly.
  • Not responding to light: The photoresistor spacing is non-standard — make sure both legs are making good contact.
  • Subtle changes: Try using a flashlight or covering the sensor completely for more dramatic results.

Experiments to Try

  • Uncomment autoTune() to let the Arduino automatically calibrate to your lighting conditions.
  • Use the sensor to trigger actions at specific light thresholds (e.g., turn on a "night light" when dark).

Izinto

8
  • 1
    SparkFun Inventor's Kit - V3.2ikhomishini engu-10%
    1 ikhithi
    $108.84
  • 2
    Breadboardikhomishini engu-10%
    1 ucezu
    Magento Legacy Storeships internationally
    kusukela ku-$9.76
  • 2
    Jumper Wiresikhomishini engu-10%
    5 izicucu
    Magento Legacy Storeships internationally
    kusukela ku-$4.27
  • 3
    Arduino Uno R3ikhomishini engu-10%
    1 ucezu
    Magento Legacy Storeships internationally
    kusukela ku-$27.80
  • LDR Photoresistor
    1 ucezu
    Isibambeli
  • 5mm LEDikhomishini engu-10%
    1 ucezu
    Magento Legacy Storeships internationally
    kusukela ku-$3.66
  • 330 Ohm Resistor
    1 ucezu
    Isibambeli
  • 10K Ohm Resistorikhomishini engu-10%
    1 ucezu
    Magento Legacy Storeships internationally
    kusukela ku-$1.22

Amathuluzi Adingekayo

1
Isamba Esilinganiselwe
Lokho umenzi akuthenga. Izinto ezikhonjiswa ngaphandle kwentengo uzithola lapho uzithenga khona.
$108.84

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