Quick Start#

This guide walks through creating a PyMCU project from scratch, building it, and flashing to an Arduino Uno (ATmega328P).

1. Create a new project#

pymcu new blink_led
cd blink_led

pymcu new prompts you to choose a target chip and sets up:

  • src/main.py — entry-point source file

  • pyproject.toml — project configuration

  • .vscode/tasks.json — VS Code build/flash tasks

  • .gitignore

The generated pyproject.toml for Arduino Uno:

[tool.pymcu]
chip      = "atmega328p"
frequency = 16000000

[tool.pymcu.programmer]
name     = "avrdude"
protocol = "arduino"
baudrate = 115200

2. Write your program#

Edit src/main.py:

from pymcu.hal.gpio import Pin
from pymcu.time import delay_ms

def main():
    led = Pin("PB5", Pin.OUT)   # Arduino Uno built-in LED (D13)
    while True:
        led.toggle()
        delay_ms(500)

Note

Every variable must have a type annotation. Pin.OUT, Pin.IN, etc. are compile-time integer constants — no runtime class exists.

3. Build#

pymcu build

Output:

[pymcu] Compiling src/main.py → dist/firmware.hex
[pymcu] Flash: 124 bytes  SRAM: 0 bytes  (ATmega328P)

The compiled .hex file is in dist/firmware.hex.

4. Flash#

Connect your Arduino Uno via USB, then:

pymcu flash --port /dev/cu.usbmodem*   # macOS
pymcu flash --port /dev/ttyACM0        # Linux
pymcu flash --port COM3                # Windows

The LED on pin 13 should blink at 1 Hz.

What just happened?#

Unlike MicroPython or CircuitPython, PyMCU did not upload an interpreter to your Arduino. The compiler on your PC translated your Python source directly to AVR machine code. The MCU runs that code at full clock speed — no Python runtime exists on the device.

Next steps#