Before ASCII, before binary, before computers — there was Baudot. Since 1901, teleprinters have been punching plain text into five tiny holes per letter on a roll of paper. Punch your own message, watch the tape, hear the 170 Hz telegraph tones, then test yourself decoding a mystery tape by ear and eye.
Composer Type anything — letters, numbers, punctuation. Shifts are handled automatically.
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Paper tape 5 channels per character — a hole means a punched "1" (Mark). Watch the playhead while it transmits.
punched hole (Mark / 1) sprocket holeLTRS activeFIGS active
Remote printout What the receiving teleprinter prints as the tape plays.
Codebook All 32 positions. Letters page (LTRS) and figures page (FIGS) share the same five channels. Tap a card to hear it.
Showing: Letters page
Decode challenge Hear a short tape being punched, look at the holes, and type the message you recover.
No tape yet
Tip: a fully-punched column (all 5 holes) switches the tape back to letters. A column with only the bottom-most channel switched on flips to figures. Numbers and punctuation live on the figures page.
Punchtape — Baudot Teletype Studio
Why this project?
Most people who have heard of telegraphs picture Morse code — but by 1901 the machines had moved on. Donald Murray's redesign of Émile Baudot's 5-bit code (the Baudot-Murray or ITA2 code) is what actually ran the world's telex network, the London-Washington hotline, and the Lorenz cipher machines of WWII. It is the direct ancestor of ASCII: every 5-bit stateful code, every shift key, and every "control character" in modern computing can be traced to a teleprinter keyboard. There is very little interactive material that lets you actually feel this code — so this studio punches, plays, and quizzes you on it.
What is it?
Punchtape is a hands-on emulator of a teletype. You type an ordinary message; the app encodes it into the ITA2 code, showing each character as a column of up to five holes on a roll of paper. Then it transmits the tape over a simulated wire using authentic Audio Frequency Shift Keying — a 2125 Hz tone when a channel is punched (Mark) and 1955 Hz when it is not (Space) — exactly how RTTY radios worked. A second pane simulates the receiving teleprinter, printing your text character by character. A codebook shows every one of the 32 code positions, and a decode challenge turns the process around: you listen to and inspect a mystery tape and have to recover the text.
How does it work?
The code: ITA2 sends 5 bits per character, but only 32 patterns exist for 26 letters + digits + punctuation. The trick is two "pages". The LTRS position (all five holes) selects the letters page; the FIGS position (bottom hole only) selects the figures page. The encoder inserts a page-switch character only when the character you type lives on a different page from the current one.
The tape: each column is a character. A hole in channel i means bit i = 1 (Mark). The encoder walks your text left to right, tracking the current page and emitting the right 5-bit column — plus the switch column when the page changes.
The wire: each 5-bit character is framed the classic 5N2 way — one start bit, five data bits (least significant first), two stop bits. The Web Audio API drives an oscillator at 2125 Hz for Mark and 1955 Hz for Space, stepped through each bit at the chosen baud rate. The oscilloscope canvas just plots the current tone.
The decoder (quiz): the receiver state machine does the reverse — it reads columns, applies page switches, and maps each 5-bit value back to a glyph. In the challenge you run that machine in your head.
No server: everything is plain HTML/CSS/JS. There is no backend, no network calls, and no data leaves your browser.
How to use it
On the Punch & Send tab, type a message (or press "Load sample message").
Watch the paper tape build itself. Holes appear as you type; page-switch columns are tinted.
Set the speed with the Baud slider (45.45 and 75 were classic rates; here 20–120). Press Transmit tape to hear and watch the AFSK tones, follow the playhead, and see the remote printout fill in. Press Stop to cut it off.
Open the Codebook to see all 32 positions. Tap any card to hear its two tones. Toggle between the letters and figures pages.
On the Decode Challenge tab, press New tape, listen with Play tape, study the holes, type your best decode, and hit Check. Stuck? Reveal answer shows the text and the exact columns it used.