#include <Wire.h>

// PIR Motion Sensor connected to Digital Pin D10
const int pirPin = D10;

// Optional: LED indicator (D13 is built-in LED on XIAO)
const int ledPin = LED_BUILTIN;

// Variable to store previous PIR state (for motion detection)
int previousState = LOW;

void setup() {
  // Initialize Serial communication at 115200 baud
  Serial.begin(115200);
  delay(1000);
  
  // Configure PIR pin as INPUT
  pinMode(pirPin, INPUT);
  
  // Configure LED pin as OUTPUT
  pinMode(ledPin, OUTPUT);
  digitalWrite(ledPin, LOW);
  
  Serial.println("=== PIR (Passive Infrared) Motion Sensor Analysis ===");
  Serial.println("Detecting motion via digital HIGH/LOW signal");
  Serial.println("PIR pin: D10 (digital input)");
  Serial.println("LED pin: D13 (built-in LED - indicates motion)");
  Serial.println("");
  Serial.println("Waiting for PIR warm-up (30-60 seconds)...");
  delay(2000);
  
  Serial.println("Time(ms)\tPIR State\tMotion Detected");
  Serial.println("=".repeat(50));
}

void loop() {
  // Read digital value from PIR sensor
  // HIGH = motion detected
  // LOW = no motion
  int pirState = digitalRead(pirPin);
  
  // Get current timestamp
  unsigned long currentTime = millis();
  
  // Print current state
  Serial.print(currentTime);
  Serial.print("\t");
  Serial.print(pirState);
  Serial.print("\t\t");
  
  if (pirState == HIGH) {
    Serial.println("YES - Motion Detected!");
    digitalWrite(ledPin, HIGH); // Turn on LED
  } else {
    Serial.println("NO - No Motion");
    digitalWrite(ledPin, LOW);  // Turn off LED
  }
  
  // Detect state change (edge detection)
  if (pirState != previousState) {
    Serial.print(">>> STATE CHANGE at ");
    Serial.print(currentTime);
    Serial.print("ms: ");
    
    if (pirState == HIGH) {
      Serial.println("MOTION DETECTED (LOW → HIGH transition)");
    } else {
      Serial.println("MOTION STOPPED (HIGH → LOW transition)");
    }
    
    // Update previous state
    previousState = pirState;
  }
  
  // Delay 500ms between readings (2 readings per second)
  delay(500);
}

/*
CIRCUIT CONFIGURATION:
======================
PIR Sensor Pin Configuration:
- VCC (5V or 3.3V) → Power pin
- GND              → Ground pin
- OUT (Signal)     → D10 (digital input pin)
- Time Delay Potentiometer (purple): Adjusts hold-on time (3-300 seconds)
- Sensitivity Potentiometer (orange): Adjusts detection range (3-7 meters)
- Trigger Mode Jumper (pink): Select single/repeated trigger

XIAO Configuration:
- D10 reads the digital output from PIR
- Pull-up resistor typically NOT needed (PIR output is TTL-compatible)
- LED on D13 provides visual feedback of motion detection

EXPECTED BEHAVIOR:
==================
- No motion:     Output: LOW (0V),  LED: OFF
- Motion:        Output: HIGH (5V), LED: ON
- After timeout: Output: LOW,       LED: OFF

The DISCRETE HIGH/LOW output is characteristic of DIGITAL signals.
No intermediate values—pure binary state change.

KEY DIFFERENCES FROM ANALOG (LDR):
==================================
1. PIR: Binary (2 states)    vs    LDR: Continuous (4096 levels)
2. PIR: No proportional info vs    LDR: Proportional to light
3. PIR: Event-based (motion) vs    LDR: Measurement-based (intensity)

TROUBLESHOOTING:
================
If PIR doesn't detect motion:
1. Wait 30-60 seconds for warm-up period
2. Adjust sensitivity potentiometer (clockwise = more sensitive)
3. Ensure movement is not too slow (PIR detects IR gradient changes)
4. Check voltage: PIR needs 5V (can damage if powered at 3.3V only)
*/