BLE Attendance Hardware

This repository contains the firmware and hardware details for the ESP32 and nRF52840 prototypes of a Bluetooth Low Energy (BLE) attendance system.

This project is designed to automate attendance by assigning students a wearable BLE Tag (beacon) and using a network of Classroom Scanners to detect their presence. The scanners log entry/exit events, timestamp them, and forward them to a central backend server.

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System Architecture

The system consists of three main parts:

1. BLE Tag (nRF52840): Beacon that continuously broadcasts its unique ID.
2. Classroom Scanner (Dual ESP32): A two-part node that receives BLE signals and sends them to the network.
   • ESP32-A (Scanner): Scans for BLE broadcasts, filters for known tags, and adds an accurate timestamp (via an RTC Module).
   • ESP32-B (Wi-Fi): Receives data from ESP32-A via ESP-NOW and POSTs it (as JSON) to the backend API.
3. Backend Server (Rails API): A central server that receives the JSON data and records the attendance.

Data Flow

[nRF52840 Tag] $\to$ (BLE Broadcast) $\to$ [ESP32-A Scanner + RTC] $\to$ (ESP-NOW) $\to$ [ESP32-B Wi-Fi] $\to$ (HTTP POST) $\to$ [Rails API]

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Hardware Bill of Materials

1. BLE Tag (Beacon)

Component	Specification
Microcontroller	nRF52840 ProMicro Dev Board V2
Battery	3.7V LiPo (501515 80mAh)
Enclosure	3D Printed Keyfob Case

Design

2. Classroom Scanner

Component	Specification
Scanner Node	ESP32 Dev Board
Wi-Fi Node	ESP32 Dev Board
Timekeeping	DS3231 RTC Module
Enclosure	3D Printed Case

Design

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Firmware

This is a PlatformIO project. All firmware source code is located in the src/ directory.

• platformio.ini: The project configuration file. It defines the boards (nRF52840, ESP32), framework (Arduino), and all required libraries

• src/ble_tag_nrf52840.cpp (BLE Tag):

  • Firmware for the nRF52840 beacon.
  • It initializes the chip as a BLE server and periodically broadcasts an iBeacon frame.
  • This specific frame format allows scanners to efficiently identify the tag.

• src/esp32a_scanner.cpp (Scanner Node):

  • Firmware for the ESP32-A, which handles all real-time sensing.
  • Continuously scans for BLE advertisements.
  • Filters for the specific iBeacons broadcast by the tags.
  • Queries the DS3231 RTC for an accurate timestamp upon detection.
  • Sends the event data (tag ID, timestamp) to ESP32-B via ESP-NOW.

• src/esp32b_wifi.cpp (Wi-Fi Node):

  • Firmware for the ESP32-B, which handles all network communication.
  • Receives data packets from ESP32-A via ESP-NOW.
  • Connects to the local Wi-Fi network.
  • Formats the data as a JSON payload and sends it to the Rails API via an HTTP POST request.