MorseReader

Classic Morse — Protocol and Transmitter

Back to MorseReader Support

Classic Morse supports letters A–Z, digits 0–9, and spaces. MorseReader estimates the dot duration automatically; a known dot duration can also be entered manually in milliseconds. Unsupported punctuation is not decoded in this mode.

Timing

Let D be one dot period:

dot:                    ON  D
dash:                   ON  3D
between marks:          OFF D
between letters:        OFF 3D
between words:          OFF 7D

The letter A (.-) is therefore:

ON D | OFF D | ON 3D

Start with D = 100 ms. Slower periods are useful for initial setup or difficult optical conditions. The transmitter must not add an intra-character gap after the final mark; the next gap is the complete 3D letter gap or 7D word gap.

Automatic timing waits for several pulses and gaps, fits them to the legal Morse multiples, and can replace an initially plausible clock when subsequent evidence fits another period substantially better. This normally takes about 1.5 seconds of usable transitions. A single isolated pulse is still ambiguous, so enter the known dot duration and press Apply for very short captures.

Python transmitter example

Replace set_led() with the GPIO operation appropriate for the device.

import time

D = 0.100
ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
CODES = """
.- -... -.-. -.. . ..-. --. .... .. .--- -.- .-.. -- -.
--- .--. --.- .-. ... - ..- ...- .-- -..- -.-- --..
----- .---- ..--- ...-- ....- ..... -.... --... ---.. ----.
""".split()
MORSE = dict(zip(ALPHABET, CODES))

def set_led(on: bool) -> None:
    # Example: gpio.write(LED_PIN, 1 if on else 0)
    pass

def level(on: bool, duration: float) -> None:
    set_led(on)
    time.sleep(duration)

def send(message: str) -> None:
    words = message.upper().split()
    for word_number, word in enumerate(words):
        for letter_number, letter in enumerate(word):
            code = MORSE[letter]
            for mark_number, mark in enumerate(code):
                level(True, D if mark == "." else 3 * D)
                if mark_number + 1 < len(code):
                    level(False, D)
            if letter_number + 1 < len(word):
                level(False, 3 * D)
        if word_number + 1 < len(words):
            level(False, 7 * D)
    set_led(False)

send("HELLO 123")

Animated example

Open the Classic Morse test page to view and test the accompanying SVG LED animation.

Reception tips