#include <Wire.h>

// LDR Sensor connected to Analog Pin A0
const int ldrPin = A0;

// Reference voltage for XIAO nRF52840
const float vRef = 3.3;
const int adcMax = 4095; // 12-bit ADC

void setup() {
  // Initialize Serial communication at 115200 baud
  Serial.begin(115200);
  delay(1000);
  
  Serial.println("=== LDR (Light Dependent Resistor) Analysis ===");
  Serial.println("Reading analog values from light sensor");
  Serial.println("Connect LDR to A0 (via voltage divider with 10kΩ resistor)");
  Serial.println("");
  Serial.println("Time(ms)\tRaw Value\tVoltage(V)\tLight Level");
  Serial.println("=".repeat(55));
}

void loop() {
  // Read raw ADC value from LDR
  int rawValue = analogRead(ldrPin);
  
  // Convert ADC value to voltage
  // Formula: V = (ADC_reading / ADC_max) * Vref
  float voltage = (rawValue / (float)adcMax) * vRef;
  
  // Convert voltage back to estimated light level (0-100%)
  // Lower voltage = high light (low resistance)
  // Higher voltage = low light (high resistance)
  float lightPercent = (1.0 - (voltage / vRef)) * 100.0;
  
  // Constrain to 0-100 range
  if (lightPercent < 0) lightPercent = 0;
  if (lightPercent > 100) lightPercent = 100;
  
  // Print data with timestamp
  unsigned long currentTime = millis();
  Serial.print(currentTime);
  Serial.print("\t");
  Serial.print(rawValue);
  Serial.print("\t");
  Serial.print(voltage, 3);
  Serial.print("\t");
  Serial.print(lightPercent, 1);
  Serial.println("%");
  
  // Delay 100ms between readings (10 readings per second)
  delay(100);
}

/*
CIRCUIT CONFIGURATION:
======================
LDR Pin Configuration:
- LDR_End1 → VCC (3.3V)
- LDR_End2 → A0 (analog input)
- 10kΩ Resistor → From A0 to GND
- This forms a voltage divider

This setup allows XIAO to read continuous analog voltage
that varies with light intensity. Use oscilloscope on A0
to observe real-time waveform changes.

EXPECTED BEHAVIOR:
==================
- Bright light:    Raw: 200-500,   Voltage: 0.2-0.4V,  Light: 75-95%
- Ambient light:   Raw: 1000-2000, Voltage: 0.8-1.6V,  Light: 25-75%
- Covered/Dark:    Raw: 2500-4000, Voltage: 2.0-3.2V,  Light: 0-25%

The continuous voltage output is characteristic of ANALOG signals.
No discrete steps—purely proportional to light intensity.
*/