Convert text to tap code and decode tap code back to text. Uses the 5x5 Polybius square cipher system with dot notation.
Tap code is a simple cipher system based on a 5x5 grid (Polybius square) where each letter is represented by two numbers indicating its row and column position. The code is transmitted through taps or knocks, making it useful for covert communication when visual or verbal methods aren't available.
The alphabet (excluding K, which shares C's position) is arranged in a 5x5 grid. Each letter is encoded as two sets of taps: the first indicates the row, the second indicates the column. For example, 'A' is position (1,1), represented as one tap, pause, one tap. In written form, this is commonly shown as dots or numbers.
Tap code gained prominence during the Vietnam War when American POWs used it to communicate through prison walls. The system's simplicity and effectiveness made it ideal for situations where prisoners could only communicate through sound.
HELLO
.. ... / . ..... / .-.. .-.. / .-.. .-.. / --- / (Dots notation) H = (2,3), E = (1,5), L = (3,1), L = (3,1), O = (3,4)
SOS
4-4 / 3-4 / 4-4 (Numbers with dash notation)
.. ... / .. / (Tap code input)
HI
TAP CODE
4-4 1-1 4-1 / 1-3 3-4 1-4 1-5 (Numbers with dash, word separator: space)
The standard 5x5 Polybius square used in tap code:
| 1 | 2 | 3 | 4 | 5 | |
| 1 | A | B | C/K | D | E |
| 2 | F | G | H | I | J |
| 3 | L | M | N | O | P |
| 4 | Q | R | S | T | U |
| 5 | V | W | X | Y | Z |
Note: The letters C and K share the same position (1,3). When decoding, context determines which letter is intended, though C is typically used by default.
Tap code uses a 5x5 grid system where each letter is represented by two numbers (row and column), transmitted as taps. Morse code uses unique patterns of dots and dashes for each letter. Tap code is simpler to learn and use without equipment, making it ideal for covert communication through walls or pipes.
The 5x5 grid has 25 positions but the English alphabet has 26 letters. Traditionally, C and K share position (1,3) because they often make similar sounds. When decoding, C is typically used by default, and context helps determine if K was intended.
Numbers aren't directly part of the 5x5 grid. They're typically spelled out as words (ONE, TWO, THREE, etc.) and then encoded as letters. Some systems use special conventions for numbers, but spelling them out is the most common approach.
American POWs during the Vietnam War used tap code to communicate through prison walls by tapping with their knuckles or other objects. The system's simplicity meant it could be learned quickly and used without any tools. Prisoners would tap out messages letter by letter, with pauses distinguishing between the row and column taps.
Dot notation (. .. / ... ....) is often easiest for beginners because it visually represents the actual taps. Each dot represents one tap, and the space between groups shows the pause between row and column. Numbers with dashes (1-2 / 3-4) are more compact and easier to write quickly.
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