4 ms·
POW's who knew more code still resorted to a new "tap code" because dot, dash, pause can't quickly be encoded with simple tap and pause.
by Retric 3y ago
POW's who knew more code still resorted to a new "tap code" because dot, dash, pause can't quickly be encoded with simple tap and pause.
- WalterBright 3y agoTap and scrape. Or taptap for dit, tap tap for dah.
- Retric 3y agoI realize why you think this might work but understand people went with a new system for multiple reasons. First the goal is for the guards not to hear what your doing or just to hear seemingly random tapping. Scrape etc means your producing two different types and levels of noise making patterns more obvious and it's harder to control who can hear. Also what matters is time not the number of taps. One common encoding was 1 to 5 taps then pause followed by 1 to 5 taps and another pause for each letter thus averaging 6 taps and two short pauses per letter. Morse code generally means 4 dots or dashes per letter so now you have 4 to 8 taps ie ~6 taps, but far more pauses in alternate encodings.
- WalterBright 3y agoI'm not sure the guards would be so stupid as to not know what the tapping means. It may be hard to tell where the tapping is coming from, though. > averaging 6 taps and two short pauses per letter This would be true if the letters are used with equal frequency. But they are not. Morse encoding uses short sequences for more common letters and longer ones for less common letters. For example, Morse E is dot, and T is dash. https://en.wikipedia.org/wiki/Morse_code#/media/File:International_Morse_Code.svg https://en.wikipedia.org/wiki/Morse_code#/media/File:Interna... For tap code, E is 5-1 and T is 4-4. https://www.inverse.com/article/11684-the-flash-and-tap-codes-a-brief-history-of-how-vietnam-pows-communicated https://www.inverse.com/article/11684-the-flash-and-tap-code... The advantage to tap code is it is easier to learn. Which, of course, also makes it easier for the screws to learn it and "tap" into those communications.
- Retric 3y agoMoving which letters are the most frequency would help tap encoding but the much worse Morse encoding more than accounts for this. With tap encoding you need 1 unit for tap, 1 unit for pause between sections and 2 units for pauses between letters. Thus A is 1 + 1 + 1 + 2 = 5 units 2 letters take 6 units, 2 letters take 7 ... etc and only one Z takes sits at 5 + 1 + 5 + 2 = 13. (The exception is C and K share the same encoding at 1 + 1 + 3 + 2 = 7 units.) Average is ~9 units before considering letter frequency. For Morse the best you can do is tap and 1, 2, or 3 units of time for pauses. Let's assume tap takes 1 units. Pauses between dot's and dash are the most common pause so that's 1 unit. The pause between taps on a dash the next most common and uses 2 units, and the pause between letters is 3 units -1 because you don't need the short pause after a dot or dash. In effect a tap is 2 units (tap pause) dash is 5 units (tap, pause, pause, tap, pause) on it's own and every letter has a penalty of 2. So E is now easily beats tap encoding at 2 + 2 = 4, T is (5 + 2) = 7, but things get much worse, The reasonably common C is 5 + 2 + 5 + 2 + 2 = 16. With the worst case Q sitting in at an abysmal 5 + 5 + 2 + 5 + 2 = 19. And that's if you can keep all the taps and pauses strait, I would be shocked if most people could actually pull off Q most of the time. Feel free to do the time calculation on this sentence for each encoring, Morse code ends up far worse. PS: Did some editing in the first 16 minutes after posting.
- WalterBright 3y ago> In effect a tap is 2 units (tap pause) dash is 5 units (tap, pause, pause, tap, pause) on it's own and every letter has a penalty of 2. See my other post in this thread about tap for dit and taptap for dah. This shortens the time. A dash would be 3 units - tap tap pause, not 5. > I would be shocked if most people could actually pull off Q most of the time An experience Morse operator doesn't attempt to decode Morse. His brain is trained to shortcut it and the letters are formed automatically, just like a skilled piano player is not actually aware of his finger movements or the individual notes. I suggest tapping with a pencil to compare rather than trying a mathematical approach. Try SOS for example. I don't see a tap taking the same time as a pause. You can do a double tap in the same time period as a tap-pause easily enough. The tap itself doesn't take time.
- WalterBright 3y agoP.S. After experimenting a bit, tap for dit and taptap for dash seems to work fine. For fun, get a pencil and tap SOS on your desk (or rattle your jewelry): tap tap tap taptap taptap taptap tap tap tap If you don't have a pencil, bang your cell phone instead! Hey, that gives me another inspiration. Don't need a rocker switch to enter Morse in your phone. Phones have an accelerometer, just bang the phone!
- kragen 3y agoalso a microphone if you like this, you might like 'magic boxes and secret knocks' https://www.mail-archive.com/kragen-tol@canonical.org/msg00046.html https://www.mail-archive.com/kragen-tol@canonical.org/msg000...
- WalterBright 3y agoI didn't think about the mike. Nice.
- kragen 3y agothanks! i had the advantage (?) of writing that before cellphones had accelerometers so i had to think up something else. haven't implemented it yet, tho
- kqr 3y agoThis is my annoyance when people talk about knocking in morse code. Though I suppose WalterBright in a sibling comment solved that handily.