📘 STM32 OLED I2C Interfacing (Register Level – No HAL)

This project demonstrates interfacing a 128×64 OLED display (SSD1306) with STM32F446RE using pure register-level programming.

🚫 No HAL 🚫 No CubeMX ✅ Bare-metal registers only

If you want to understand how I2C really works inside STM32, this project is your playground.

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🎯 What This Project Does

• Initializes I2C1 using STM32 registers

• Communicates with SSD1306 OLED over I2C

• Implements:

  • OLED initialization sequence
  • Screen clear
  • Cursor positioning
  • Character & string rendering

• Uses a custom 6×8 ASCII font

• Displays multiple strings on different OLED pages

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🧰 Hardware Requirements

Component	Description
MCU	STM32F446RE (Nucleo)
Display	128×64 OLED (SSD1306, I2C)
Interface	I2C
Wires	Jumper wires

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🔌 Pin Connections

OLED Pin	STM32F446RE Pin
VCC	3.3V
GND	GND
SDA	PB9 (I2C1 SDA)
SCL	PB8 (I2C1 SCL)

📌 Note: PB8 & PB9 are configured as AF4 Open-Drain with Pull-Up, exactly how I2C expects.

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🧠 Core Concepts Covered

This repo is not just about “making OLED work”—it teaches how it works.

1️⃣ SysTick Delay (Register Based)

void delay_ms(uint32_t ms);

• Uses SysTick timer
• No HAL delay calls
• Accurate millisecond delays

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2️⃣ I2C Initialization (Bare Metal)

void I2C1_Init(void);

Configures:

• GPIOB alternate function
• Open-drain outputs
• APB1 clock for I2C
• Clock control, rise time, CCR

You’ll finally understand:

“Why these I2C registers exist in the first place.”

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3️⃣ Low-Level I2C Transactions

Function	Purpose
I2C_Start()	Generate START condition
I2C_Address()	Send OLED slave address
I2C_Write()	Transmit data/command
I2C_Stop()	Generate STOP condition

This mirrors actual I2C timing diagrams, not abstract HAL calls.

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4️⃣ OLED Control Logic

Function	Role
OLED_Command()	Send command byte
OLED_Data()	Send pixel data
OLED_Init()	SSD1306 initialization
OLED_Clear()	Clear full screen
OLED_SetCursor()	Page & column control

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5️⃣ Font Rendering Engine

• Custom 6×8 ASCII font
• Each character = 6 bytes
• Stored in Flash
• Drawn column-by-column

void OLED_DrawChar(char c);
void OLED_DrawString(uint8_t x, uint8_t page, const char *str);

This teaches how text is actually rendered on pixel displays.

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🖥️ Output Preview

The OLED displays:

STM32F446
STM32 OLED I2C
DANIEL RAJ.C
_____________

Each line is written on a different OLED page.

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▶️ How to Run This Project

1. Open STM32CubeIDE
2. Create a bare STM32 project
3. Replace main.c with the provided code
4. Build & Flash
5. Power the board
6. Watch the OLED come alive ✨

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🧩 Why Register Coding?

Let’s be real:

• HAL = fast results
• Registers = real understanding

This project helps you:

• Read reference manuals confidently
• Debug hardware issues faster
• Crack interviews that ask 👉 “How does I2C work internally?”

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🚀 Who This Repo Is For

• STM32 beginners stepping beyond HAL
• Embedded learners who want strong fundamentals
• Anyone preparing for embedded interviews
• Curious minds who love bare-metal control

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📌 Future Enhancements (Ideas)

• Scrolling text
• Inverted display mode
• Bigger fonts
• Multi-line text wrapping
• I2C error handling

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📜 License

This project is MIT- Licenced and free to use for learning and experimentation.

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