🔎 Quick navigation: Overview • Hardware • Getting Started • Projects • State Machine • Docs • Acknowledgements
A personal project to learn bare metal AVR C development, writing directly to hardware registers without any framework or abstraction layer. The ATmega644P runs at 20 MHz on a custom PCB designed by Richard Reeves with an external crystal, LM317T voltage regulator and 10-way headers breaking out all 32 I/O pins.
Projects progress from a basic LED blink through GPIO manipulation, button polling, interrupt-driven input, software PWM and ADC, building towards a full nine-mode state machine that includes a reaction game and a Tetris melody synced to LEDs. All code targets the ATmega644P and can be built with either PlatformIO in VS Code or Microchip Studio 7. See WORKFLOW.md for the full setup and flash guide.
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| C | Embedded C | PlatformIO | VS Code | Microchip Studio | Git | GitHub |
| Item | Detail |
|---|---|
| MCU | ATmega644P DIP-40, 20 MHz external crystal |
| PCB | Richard Reeves AVR Project PCB 2019 with LM317T regulator |
| Programmer | Pololu USB AVR Programmer v2.1 via STK500v2 on COM4 |
The breadboard components (LEDs, button, buzzer) are a temporary configuration used for learning and change between sessions. See docs/wiring.md for the current breadboard connections and header pin assignments. Full PCB component list, connector pinout and power supply circuit are in hardware/pcb_notes.md.
- Clone the repo and choose an IDE: VS Code with PlatformIO or Microchip Studio 7.
- Follow the full setup guide in WORKFLOW.md. It covers prerequisites, environment switching, build tasks and flash commands.
- Connect the Pololu programmer to the ISP header (J1) on the PCB and to a USB port (COM4).
- Select a project from the Projects table below and build.
Manual flash command if needed:
C:\avrdude\avrdude.exe -c stk500v2 -p m644p -P COM4 -B 10 -V -U flash:w:<project>.hex:i
The -B 10 flag slows the ISP clock to ~50 kHz, which is required to avoid timeout errors with the Pololu programmer. See WORKFLOW.md for the full flag reference and troubleshooting steps.
| # | File | Description | Key Concepts |
|---|---|---|---|
| 0 | 00_fuse_test.c | Fuse configuration and restoration reference | Fuse bits, clock source, avrdude -F flag |
| 1 | 01_blink.c | Double blink on PB0 | DDRB, PORTB, _delay_ms |
| 2 | 02_led_cycle.c | Five LEDs cycling sequentially | Multi-pin output, bit shifting |
| 3 | 03_button_polling.c | Button drives buzzer via polling | PIND, input reading, active buzzer |
| 4 | 04_interrupt_buzzer.c | Button drives buzzer via INT0 | ISR, EICRA, EIMSK, sei() |
| 5 | 05_state_machine_basic.c | Four-mode state machine (initial build) | enum, ISR, debounce, switch |
| 6 | 06_state_machine.c | Nine-mode state machine (full build) | PWM, ADC, reaction game, Tetris melody |
Source files live in projects/learning_projects/ (one folder per project). The active project is also copied into platformio/src/ for building. See WORKFLOW.md for how to switch between projects.
06_state_machine.c cycles through nine modes on each button press. Mode state is held in a volatile variable updated inside an INT0 ISR with software debounce.
| Mode | Name | Description |
|---|---|---|
| 0 | Chase | LEDs light one by one in sequence |
| 1 | Blink All | All five LEDs blink together |
| 2 | Alternate | Odd and even LEDs alternate |
| 3 | PWM Fade | All LEDs fade in and out via software PWM |
| 4 | Knight Rider | Single LED sweeps left to right and back |
| 5 | Binary Counter | LEDs count 0 to 31 in binary |
| 6 | Random | LEDs display random patterns seeded by ADC noise |
| 7 | Reaction Game | Press button when green LED lights to win |
| 8 | Tetris Melody | Tetris theme plays with LEDs synced to each note |
| Document | Description |
|---|---|
| Build and Flash Workflow | Full VS Code/PlatformIO and Microchip Studio setup, environment switching, build tasks and troubleshooting |
| Wiring Reference | Current breadboard connections and header pin tables |
| Hardware Notes | Fuse settings, ISP clock speed, register map and ADC configuration |
| PCB Full Reference | Component list, connector pinout, power supply circuit and soldering order |
| PCB Schematic PDF | Original PCB schematic and layout PDF for the Richard Reeves AVR Project PCB 2019 |
| ATmega644P Datasheet | Official Microchip datasheet for the ATmega644P |
| C Operators Reference PDF | Printable C operator reference card |
Each session has a notes.md (reference) and a lab.md (hands-on tasks).
| Session | Topic | Notes | Lab |
|---|---|---|---|
| 1 | Introduction to AVR C | notes | lab |
| 2 | Bit Shifting, Arrays and Data Types | notes | lab |
| 3 | Inputs, Bit Masking and Interrupts | notes | lab |
| 4 | Timers: Overflow and Output Compare | notes | lab |
| 5 | Hardware PWM | notes | lab |
| 6 | UART Serial Transmission | notes | lab |
| 7 | Analogue to Digital Conversion | notes | lab |
| 8 | UART Serial Reception | notes | lab |
| Document | Description |
|---|---|
| C Operators Reference | Arithmetic, bitwise, relational and assignment operator tables with AVR examples and precedence table |
| Hardware Reference | PCB overview, power supply, headers (J1 to J7), crystal, fuse summary and component list |
Richard Reeves, lab technician at Aston University, designed the AVR Project PCB and provided components and guidance.
Open an issue in this repository for questions or bugs.
You can also reach me directly at eng@isaacadjei.me or via my website contact page.