Stage chrono

⏱️ ESP32 Giant 24V COB LED Chronometer & Industrial PCB

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An end-to-end industrial-grade embedded system featuring a 6-digit giant 7-segment display driven by high-lumen 24V COB LED strips, a custom modular KiCad 10 PCB, an ESP32-WROVER-E dual-core controller hosting an asynchronous real-time Web dashboard, and SIM800L GSM cellular telemetry.

Designed, developed, and fabricated by Bacem AMEUR (National Engineering School of Monastir - ENIM) during an engineering internship at Chrono Sports Events.

📸 Hardware Showcase & Gallery

Figure 1: Photorealistic 3D CAD render of the assembled CHRONO_01 board in KiCad 10.

Figure 2: Complete electrical schematic (ESP32, 74HC595 cascade, ULN2803A drivers, LM2596 power regulation).

Figure 3: Double-sided physical PCB fabricated via chemical etching (Left: Component side F.Cu, Right: Solder side B.Cu).

📑 Table of Contents

• Hardware Showcase & Gallery
• Key Features
• System Architecture
• Hardware & Electrical Engineering
• Firmware & Dual-Core Architecture
• Web Dashboard UI
• Repository Structure
• Bill of Materials (BOM) & Economic Study
• Installation & Getting Started
• Author & License

🌟 Key Features

• High-Visibility Giant Display: 6 digits (HH:MM:SS) using high-density 24V COB LED strips for uniform, neon-like illumination without individual LED hotspots.
• Dual-Core Asynchronous Firmware:
  • Core 0: Manages Wi-Fi Soft-AP (SSID: CHRONO_01) and serves an asynchronous HTML5/CSS3/JavaScript dark-mode web application via ESPAsyncWebServer.
  • Core 1: Executes deterministic $1,\text{ms}$ chronometer counting, high-speed SPI shift register cascading, and non-blocking UART GSM AT parsing.
• High-Power Common-Anode Driving: 6 daisy-chained 74HC595 serial shift registers interfaced with 6 ULN2803A Darlington sink arrays, controlling 42 independent 24V segments at up to $500,\text{mA}$ per channel.
• GSM/SMS Telemetry: Integrated SIM800L cellular transceiver with a customized $1000,\mu\text{F}$ low-ESR reservoir network to absorb 2.0A TDMA RF burst current drops.
• Cost Efficiency: Sourced and built for approximately 740 TND (~€220), delivering performance comparable to turnkey commercial race scoreboards costing 3,000 to 20,000 TND.

🏛 System Architecture

 ┌─────────────────────────────────────────────────────────────────────────────┐
 │                               MAIN POWER SUPPLY                             │
 │                        (230V AC  ──>  24V DC / 2.5A SMPS)                   │
 └──────────────────────┬────────────────────────────────┬─────────────────────┘
                        │ (+24V Power Bus)               │ (+24V Input)
                        ▼                                ▼
       ┌─────────────────────────────────┐      ┌──────────────────────────────┐
       │   42x 24V COB LED SEGMENTS      │      │   LM2596 BUCK REGULATOR      │
       │   (6 Digits: A, B, C, D, E, F, G│      │   (24V DC  ──>  5.0V / 4.1V) │
       │    Common Anode Configuration)  │      └──────────────┬───────────────┘
       └────────────────▲────────────────┘                     │
                        │ Sinking Grounds (x42)                │
       ┌────────────────┴────────────────┐                     ▼
       │     6x ULN2803A DARLINGTON      │             ┌───────────────┐
       │        TRANSISTOR ARRAYS        │◄── 5V ──────┤  ESP32-WROVER │
       └────────────────▲────────────────┘             │   DUAL-CORE   │
                        │ 8-bit Parallel Out (x6)      │  (Soft-AP Web │
       ┌────────────────┴────────────────┐             │   Server +    │
       │       6x 74HC595 SERIAL         │◄── SPI ─────┤   FreeRTOS)   │
       │        SHIFT REGISTERS          │ (DATA/CLK/  └───────┬───────┘
       └─────────────────────────────────┘   LATCH)            │ UART (TX2/RX2)
                                                               ▼
                                                       ┌───────────────┐
                                                       │ SIM800L GSM   │
                                                       │ (+1000uF Cap) │
                                                       └───────────────┘

⚡ Hardware & Electrical Engineering

I/O Expansion & Power Driving

Driving 42 discrete LED segments using only 3 GPIO pins from the ESP32:

• 74HC595 Shift Registers: Cascaded in series. The serial frame ($6 \times 8 = 48,\text{bits}$) is clocked via high-speed SPI in less than $5,\mu\text{s}$.
• ULN2803A Darlington Sink Drivers: 8 open-collector channels with integrated clamp diodes per IC. Each output can sink up to $500,\text{mA}$ under $24,\text{V}$, perfectly matching the common-anode COB LED segments.

 ESP32 GPIO ────> 74HC595 (Qn) ───[2.7kΩ]───> ULN2803A (Base) ───> Sinks (-24V) to GND
                                                                           ▲
                                                  +24V Rail ───[LED Strip]─┘

Mathematical Sizing & Transient Filtering

The GSM module consumes up to $I_{\text{peak}} = 2.0,\text{A}$ in $577,\mu\text{s}$ bursts. Without adequate capacitive reservoir sizing, the voltage droops below $3.7,\text{V}$, causing brownout resets.

The required charge buffer is sized according to: $$C_1 = \frac{I_{\text{peak}} \cdot \Delta t}{\Delta V_{\text{max}}} = \frac{2.0,\text{A} \times 577,\mu\text{s}}{0.4,\text{V}} \approx 2885,\mu\text{F}$$

Accounting for active source replenishment from the LM2596 buck converter, an effective capacitor of $1000,\mu\text{F}$ / 16V low-ESR in parallel with a $100,\text{nF}$ ceramic decoupling capacitor is placed directly at the SIM800L power pins.

Single-Sided / NPTH PCB Optimization

To support artisan local PCB chemical etching without plated through-holes (NPTH):

• Modular T-Shape Topology: Eliminates track congestion and prevents layer crossing.
• Machined-Pin Tulip Sockets: DIP sockets are elevated above the PCB top copper layer to allow top-side manual soldering with fine iron tips.
• Merged Drill Files: Excellon drill files configured with "Merge PTH and NPTH" for single-pass fabrication.

💻 Firmware & Dual-Core Architecture

The firmware is written in Arduino C++ utilizing ESP32 FreeRTOS multitasking:

📱 Web Dashboard UI

The responsive dark-theme dashboard runs entirely embedded within the ESP32 SPIFFS memory:

• Zero Internet Required: Automatically hosts a local hotspot CHRONO_01 (192.168.4.1).
• Live Synchronized Display: CSS seven-segment digital display mirroring the real physical board.
• Controls: Start, Pause, Lap Time, Split Time, Time Preset, and Display Brightness.

📂 Repository Structure

├── .gitignore
├── LICENSE
├── README.md
├── firmware/
│   ├── ChronoServer/
│   │   ├── ChronoServer.ino         # Main dual-core ESP32 firmware
│   │   └── index.html               # Embedded HTML5/CSS3/JS dashboard
│   └── tests/
│       ├── test_blink_esp32.ino     # GPIO & RTC validation test
│       └── test_sim800l_at.ino      # Hardware UART GSM pass-through test
├── hardware/
│   ├── kicad/                       # KiCad 10 schematics (.kicad_sch) and PCB (.kicad_pcb)
│   ├── gerbers/                     # Production Gerber and Excellon drill files
│   ├── schematics/
│   │   └── pinout_reference.md      # Pinout table for JST & shift registers
│   ├── bom/
│   │   └── bill_of_materials.md     # Detailed BOM and supplier breakdown
│   └── mechanical/
│       └── chassis_assembly.md      # Chassis drilling, baffles, and wiring guide
└── docs/
    ├── Journal stage 2026.pdf       # 30-day chronological internship journal
    ├── rapport_stage_2026.pdf       # Compiled official internship engineering report
    ├── stage_chrono_presentation.pdf # Oral defense slide deck
    └── report/
        ├── rapport_stage_bacem_ameur.tex # LaTeX source code
        └── figures/                 # High-resolution schematics, 3D renders & photos

💰 Bill of Materials (BOM) & Economic Study

🚀 Installation & Getting Started

1. Arduino IDE Setup

1. Install Arduino IDE 2.x.
2. Install the ESP32 Board Package (Recommended: stable version 2.0.17 via Boards Manager).
3. Board Configuration:
   • Board: ESP32 Wrover Module (or ESP32 Dev Module)
   • Flash Mode: DIO (or QIO depending on flash vendor)
   • Flash Frequency: 40MHz
   • PSRAM: Enabled
   • Partition Scheme: Default 4MB with spiffs
4. Install required libraries:
   • ESPAsyncWebServer & AsyncTCP

2. Flashing the Firmware

1. Connect the ESP32 to your PC via a Micro-USB data cable.
2. Open firmware/ChronoServer/ChronoServer.ino.
3. Select your COM port and hit Upload (➔).

3. Connecting to the Web Dashboard

1. Power on the chronometer with 24V DC.
2. On your phone or laptop, connect to the Wi-Fi network:
   • SSID: CHRONO_01
   • Password: 12345678
3. Open any web browser and navigate to:
   • http://192.168.4.1

👤 Author

Bacem AMEUR
Electrical Engineering Student — National Engineering School of Monastir (ENIM)

• 📍 Sfax / Monastir, Tunisia
• 💼 LinkedIn: linkedin.com/in/becem-ameur
• 🐙 GitHub: @becem0
• ✉️ Email: Becemameur15@gmail.com

📜 License

This project is open-source and licensed under the MIT License.