Morse Code Decoder — STM32F103

A bare-metal embedded project that decodes Morse code input from physical buttons and outputs the decoded letter over UART serial — running on an STM32F103 "Blue Pill" microcontroller.

Built using libopencm3 — an open-source peripheral library for STM32.

How It Works

1. Hold PA0 (Start button) → LED on PC13 turns ON, session begins
2. Tap PA1 (Morse button) → short tap = dot ., long tap = dash -
3. Release PA0 → LED turns OFF, input is decoded and printed over serial

Dot/dash threshold: 300ms — tap under 300ms is a dot, over is a dash.

Hardware

Pin	Function
PA0	Start/Stop button
PA1	Morse input button
PA9	USART1 TX (serial out)
PC13	Onboard LED

Board: STM32F103C8T6 "Blue Pill"
Clock: 72MHz via external 8MHz HSE crystal + PLL
Serial: 9600 baud, 8N1

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Requirements

• ARM cross-compiler: arm-none-eabi-gcc
• libopencm3 (set up in parent directory)
• make
• ST-Link or similar flasher to upload to the board

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Build & Flash

make          # compiles morse.c → morse.elf + morse.bin

Flash to board using ST-Link:

st-flash write morse.bin 0x8000000

Or using OpenOCD:

openocd -f interface/stlink.cfg -f target/stm32f1x.cfg \
        -c "program morse.elf verify reset exit"

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Serial Output

Connect to USART1 TX (PA9) with a USB-to-TTL adapter at 9600 baud.

Example output:

Morse Code Ready...
.-      A
-...    B
...     S

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Morse Table

The decoder supports all 26 letters (A–Z) plus space:

Letter	Code	Letter	Code
A	.-	N	-.
B	-...	O	---
C	-.-.	P	.--.
D	-..	Q	--.-
E	.	R	.-.
F	..-.	S	...
G	--.	T	-
H	....	U	..-
I	..	V	...-
J	.---	W	.--
K	-.-	X	-..-
L	.-..	Y	-.--
M	--	Z	--..

Unknown patterns output ?.

Project Structure

morseCode/ ├── morse.c ← main source code ├── Makefile ← build config ├── morse.elf ← compiled binary with debug info ├── morse.bin ← raw binary for flashing ├── morse.map ← memory map ├── morse.o ← compiled object file └── morse.d ← dependency file

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Dhanvi Vijaykumar