The prompt-first pass
The original build below records how this idea first worked. The durable lesson now targets the M5Stack Stopwatch and lives in the prompt, behavior contract, generalized tests, and hand-review checklist. Generated firmware is evidence for those sources, not the source itself.
Three days of button timing — grammar, then a stopwatch, then C25K before either — and the natural question is what all that discipline is for.
Morse is the answer with a birth certificate. It’s a timing protocol from 1844: one signal, one dimension, everything encoded in durations and silences. A straight key is the minimum viable keyboard.
The whole standard is five ratios
ITU-R M.1677-1 defines international Morse in a page: dah is three dits, gaps of one, three, and seven units separate symbols, letters, and words.
Speed is one number — words per minute, measured against the word “PARIS,” which happens to be exactly 50 units.
So unit = 1200 / WPM milliseconds, and the entire protocol scales from one division.
The decoder needs two decisions. Press length: shorter than 2 units is a dit — the midpoint between 1 and 3 gives equal tolerance both ways. Silence length: 3 units closes a letter, 7 closes a word. That’s it. The rest is a 36-entry lookup table that hasn’t changed since radio operators wore wool.
Silence is data
The interesting engineering is that most of the decoding happens when nothing is happening. The loop watches the gap since the last release grow — past 3 units it commits the letter, past 7 it commits the space. There’s no “done” button. The absence of input is the input, which makes this the purest possible exercise of day 12’s rule: timestamps, not counters, and never block the loop, because the loop is literally reading silence.
The sidetone follows the same honesty. It starts on press and stops on release — what you hear is exactly what the decoder measures. If your dah sounds short, it was short. The tone is the debugger.
What we learned
- A protocol can be five ratios and a table. Morse survives because its spec fits in a pocket.
- Silence is data. Letter and word boundaries are decoded from what didn’t happen, on a clock.
- The sidetone is the debugger. Feedback that mirrors measurement teaches faster than any error message.
- Every timing lesson was this lesson. Grammar, clocks, non-blocking loops — pointed at 1844, they decode telegraphy.