A real-time system that tracks how many people are on each floor of the library using ESP32 microcontrollers, IR break-beam sensors, and a Next.js + Firebase web dashboard.

Each floor has one Main Board and optionally one or more Support Boards. Each board reads two IR break-beam sensors mounted in a doorway to detect whether someone is entering or exiting based on which beam breaks first. Support Boards send their counts to the Main Board every 10 seconds via ESP-NOW (a peer-to-peer WiFi protocol that doesn't require a router). The Main Board aggregates all counts and writes the floor occupancy to Firebase Realtime Database every 10 seconds over HTTPS. The Next.js frontend subscribes to Firebase with an onValue() listener and updates the display the instant new data arrives.

IR Sensors → Support Board ──ESP-NOW──→ Main Board ──HTTPS──→ Firebase ──onValue()──→ Frontend
IR Sensors → Main Board ──────────────────────────────────────────────↗

USF Library Tracker/
├── esp32/
│   ├── config/
│   │   └── Config.h               # All credentials and settings — edit this before flashing
│   ├── Get_MAC_Address/
│   │   └── Get_MAC_Address.ino    # One-time utility to read ESP32 MAC address
│   ├── Main_Board/
│   │   ├── Main_Board.ino         # Flash to the initiator board on each floor
│   │   └── Config.h               # Copy of Config.h
│   └── Support_Board/
│       ├── Support_Board.ino      # Flash to all other boards on the same floor
│       └── Config.h               # Copy of Config.h
└── library-occupancy-tracker/     # Next.js web app
    ├── src/
    │   ├── app/
    │   │   ├── page.tsx           # Frontend dashboard
    │   │   ├── layout.tsx
    │   │   └── api/
    │   │       └── update-floor/
    │   │           └── route.ts   # Optional API route (not used in current build)
    │   ├── lib/
    │   │   └── firebase.ts        # Firebase initialization
    │   └── components/
    │       └── FloorCard.tsx      # Per-floor occupancy card
    └── .env.local                 # Firebase credentials for Next.js (never commit)

floors/
  Floor_1/
    current_occupancy: 42
    max_capacity:      100
    total_entries:     310
    total_exits:       268
    last_updated:      823042     ← ms since board boot
  Floor_2/
    ...

current_occupancy is clamped between 0 and max_capacity. total_entries and total_exits are cumulative since last board boot and are useful for detecting sensor drift over time.

• 2× IR break-beam sensor pairs (emitter + receiver)
• 2x 1k Ohm resistors (for pull up resistor)
• 1× ESP32 development board
• Jumper wires

Mount sensors in sequence across the doorway. Sensor A must face the corridor (outside), Sensor B must face the floor interior (inside). The order of which beam breaks first determines direction:

• A breaks first → entry
• B breaks first → exit

All settings live in Config.h. Copy this file into each sketch folder before flashing.

// Config.h

// Shared — both Main Board and Support Board
#define FLOOR_ID      "Floor_1"   // Must match Firebase path key exactly (case-sensitive)
#define MAX_CAPACITY  120          // Max occupancy for this floor
#define WIFI_CHANNEL  1            // Must match your router's channel — see Setup below

// MAC address of the Main Board for this floor
// Get this by flashing Get_MAC_Address.ino and reading Serial output
uint8_t MAIN_BOARD_MAC[] = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };

// Main Board only
#define WIFI_SSID      "your_network"
#define WIFI_PASSWORD  "your_password"
#define FIREBASE_HOST  "your-project-default-rtdb.firebaseio.com"
#define FIREBASE_AUTH  "your_database_secret"

Firebase Console → Project Settings → Service Accounts → Database secrets → Show or Add secret. This is a long random string, not the Web API Key (AIzaSy...).

Flash Main_Board.ino first. Check Serial Monitor — it will print [WiFi] Channel: X. Put that number in WIFI_CHANNEL in Config.h before flashing Support Boards.

Arduino IDE with the ESP32 board package installed is required.
Install ESP32 boards: File → Preferences → add https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json to Additional Board Manager URLs, then Tools → Board → Boards Manager → search "esp32" by Espressif → Install.

• ArduinoJson by Benoit Blanchon

1. Open Get_MAC_Address/Get_MAC_Address.ino
2. Select board: Tools → Board → ESP32 Arduino → ESP32 Dev Module
3. Select port: Tools → Port → (your ESP32's COM port)
4. Upload → open Serial Monitor at 115200 baud
5. Record the MAC address printed — this is your Main Board's MAC
6. Repeat for any other boards if needed

Fill in all values in Config.h:

• Paste the Main Board MAC into MAIN_BOARD_MAC
• Add your WiFi credentials
• Add your Firebase host and auth secret
• Leave WIFI_CHANNEL as 1 for now (you'll confirm it after first flash)

Copy Config.h into both Main_Board/ and Support_Board/ folders.

1. Open Main_Board/Main_Board.ino
2. Select the Main Board's COM port
3. Upload
4. Open Serial Monitor at 115200 baud
5. Note the channel printed: [WiFi] Channel: X
6. Update WIFI_CHANNEL in Config.h if it differs from what you set

1. Update WIFI_CHANNEL in Config.h to match what Main Board reported
2. Copy updated Config.h into Support_Board/
3. Open Support_Board/Support_Board.ino
4. Select the Support Board's COM port
5. Upload

Main Board Serial Monitor should show:

[WiFi] Connected. IP: ...
[ESP-NOW] Ready. Channel=1
[Boot] max_capacity write HTTP 200
[Boot] Main Board ready.
[ESP-NOW] Received — entries: 0  exits: 0   ← Support Board packets arriving
[Firebase] Write successful.

Support Board Serial Monitor should show:

[Boot] Support Board ready. Channel=1
[ESP-NOW] Packet queued. entries=0 exits=0

Note: onDataSent may report FAILED on the Support Board even when data arrives correctly. This is a known ESP32 quirk — when the Main Board is connected to WiFi, it briefly hops channels for beacon frames, causing the ACK to be missed. As long as the Main Board shows [ESP-NOW] Received, the system is working correctly.

For development, set your rules to open in Firebase Console → Realtime Database → Rules:

{
  "rules": {
    ".read": true,
    ".write": true
  }
}

Before going live in the library, tighten these rules to only allow writes authenticated with your database secret.

cd library-occupancy-tracker
npm install

Create .env.local in the project root:

NEXT_PUBLIC_FIREBASE_API_KEY=
NEXT_PUBLIC_FIREBASE_AUTH_DOMAIN=
NEXT_PUBLIC_FIREBASE_DATABASE_URL=
NEXT_PUBLIC_FIREBASE_PROJECT_ID=

All values are found in Firebase Console → Project Settings → General → Your apps → Firebase SDK snippet.

npm run dev

App runs at http://localhost:3000. The dashboard reads from Firebase in real time using onValue() — no polling needed. The display updates the instant the Main Board writes new data.

Each floor card shows:

• Current occupancy percentage (current_occupancy / max_capacity)
• Last updated timestamp

Keep Support Board interval shorter than Main Board interval so the Main Board always has fresh aggregated data before it writes to Firebase.

1. Get MAC address of the new floor's Main Board via Get_MAC_Address.ino
2. Create a new Config.h with the new FLOOR_ID (e.g. "Floor_2") and the new board's MAC
3. Flash Main_Board.ino to the initiator board and Support_Board.ino to any responder boards
4. Firebase will auto-create the floors/Floor_2/ node on first boot
5. Add the new floor to your frontend — add "Floor_2" wherever your floor list is defined

• last_updated stores milliseconds since board boot, not a real timestamp. For real timestamps, NTP time sync would need to be added to Main_Board.ino.
• Occupancy resets to 0 on board reboot. A daily scheduled reset (Firebase Cloud Function or Next.js cron) is recommended for production to prevent drift accumulating across days.
• If the library has more than one entrance per floor, one sensor pair per entrance is needed, each on its own board.
• setInsecure() is used for HTTPS — acceptable for an internal tool, but a proper root CA certificate should be used for a production deployment.