This project implements a complete HTTP web server on an STM32 Blue Pill (STM32F103C8T6) using the W5500 Ethernet module. The server hosts a modern web dashboard that displays real-time environmental data from a DHT11 sensor and DS3231 RTC, while also providing remote LED control through a REST API.

Key Features:

• HTTP web server on port 80 (accessible via any web browser)
• REST API endpoints for sensor data and LED control
• Real-time temperature and humidity monitoring (DHT11)
• Real-time clock and date display (DS3231)
• Remote LED control with instant feedback
• AJAX-powered auto-refresh (every 3 seconds)

Shows hardware setup and LED control via web interface

Demonstrates web dashboard with real-time sensor data and LED control

The server implements a full HTTP/1.1-compliant stack on top of the W5500's hardware TCP/IP offload engine.

1. Socket Establishment

• W5500 maintains socket 0 in SOCK_LISTEN state on port 80
• listen() initiates passive TCP open
• On SYN arrival, state transitions: LISTEN → SYNRECV → ESTABLISHED

2. HTTP Request Parsing

• Raw TCP payload extracted via recv()
• Stateless parser scans for CRLF (\r\n) delimiters
• Extracts: HTTP method (GET only), request URI, protocol version
• Query parameters and headers are parsed but unused (reserved for future)

3. Routing Logic

• Path string compared against registered endpoints
• Uses strcmp() for exact matching (no regex to save flash)
• Dispatch to handler functions via conditional branching

The DHT11 uses a single-wire protocol with precise timing:

Instead of measuring pulse width, I used a simpler approach looking at datasheet:

For each bit:

1. Wait for line to go HIGH
2. Delay exactly 40µs
3. If line still HIGH → logic 1
   If line is LOW → logic 0

To ensure the timing is not interrupted, interrupts are disabled while communicating with the sensor. The checksum provided by the sensor is used to verify data integrity.

The DS3231 is a precision Real-Time Clock (RTC) with an integrated temperature-compensated crystal oscillator and I2C interface. The driver provides two ways to access RTC data:

1. Time/Date Data: Current time (hours, minutes, seconds) and date (day, month, year)
2. Temperature Data: Built-in temperature sensor reading (±3°C accuracy)

Implementation:

• Burst read of all 7 time registers in a single I2C transaction
• BCD conversion handles register format automatically
• Data Flow: I2C Read (0x00-0x06) → 7 bytes → Convert BCD → Update time structure
• Oscillator monitoring detects power failures via status register

Note: LCD display shows formatted time/date strings and temperature in physical units. Raw BCD values are automatically converted using internal helper functions. The RTC maintains accurate time even when main power is off using a CR2032 backup battery.

• STM32_W5500_TCP_Server (Non-RTOS version)
• STM32_FreeRTOS_W5500_TCP_Server
• STM32_W5500_TCP_Client

• STM32F103 Datasheet
• STM32F103 Reference Manual
• WIZNET W5500 Datasheet
• DHT11 Sensor Datasheet
• RTC DS3231 Datasheet

• Status: Complete
• Version: v1.0
• Last Updated: April 2026

Rubin Khadka Chhetri
📧 [email protected]
🐙 GitHub: https://github.com/rubin-khadka