🛠 Lire un capteur de lumière sur A2

Objectives

Read a LilyPad light sensor (photoresistor) on an analog input and display values from 0–1023 in the Serial Monitor. You will discover the 10-bit ADC, pads A2 to A5 (the only analog inputs available on standard LilyPad boards), and the use of the FTDI adapter as a serial port.

Hardware

• 1 LilyPad SimpleSnap + 3.7 V battery
• 1 LilyPad Light Sensor
• Conductive thread or snap buttons
• FTDI adapter + Arduino IDE (Serial Monitor set to 9600 baud)

Complete Code

// Lecture du capteur de lumière sur A2 — ADC 10 bits (0..1023)
const uint8_t CAPTEUR = A2; // LilyPad classiques : A2..A5 uniquement !

void setup {
  Serial.begin(9600); // le FTDI relie la carte au moniteur série
}

void loop {
  int brut = analogRead(CAPTEUR); // sombre -> bas, lumineux -> haut (selon câblage)
  Serial.print("Lumiere : ");
  Serial.print(brut);
  Serial.print(" / 1023  ->  ");
  Serial.print(map(brut, 0, 1023, 0, 100));
  Serial.println(" %");
  delay(100);
}

Expected Verification

The Serial Monitor displays approximately ten lines per second. Covering the photoresistor with your finger causes the value to drop towards 0; illuminating it with a flashlight causes it to rise towards 1023. The values vary progressively, without erratic jumps if the snap buttons are properly pressed.

Common Errors

• Using A0 or A1: Standard LilyPad boards (Main/Simple/SimpleSnap) only expose A2 to A5; nothing happens on these pins.
• Serial Monitor set to a baud rate other than 9600: Unreadable characters.
• Misunderstanding the dark/light direction: Depending on the sensor wiring (voltage divider towards + or towards −), the value increases or decreases with light.
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