Whats a Code 1 A system of signals

What’s a Code? 1. A system of signals used to represent letters and numbers in transmitting messages. 2. A system of symbols, letters, or words given certain arbitrary meanings, used for transmitting messages requiring secrecy and brevity. -- American Heritage Dictionary

Who are these people?

Sending messages using Clicks and Clacks: Telegraph Key Western Electric Morse Code Telegraph Sounder

How does this work? When a current flows through the induction coil, the resulting magnetic field attracts an armature that is held up against a metal arm. When the current is switched off, the armature is drops to its resting position, resulting in a "click". When the current returns, the armature is raised back to the upper arm resulting in a "clack. " http: //www. answers. com

What can you do with “Clicks” and “Clacks”? Morse Code: A fast click-clack is a dot. A slow click-clack is a dash. Morse code is comprised on only two symbols. Morse code is a binary code (two symbols).

Famous Morse Codes SOS – An easy to remember distress call, similar to 911 today. SOS =. . . _ _ _. . . ‘V’ for Victory – Beethoven’s 5 th Symphony Dah Dah Daaahhhmmmm =. . . _

Samuel Morse Artist/Inventor 1830’s Note not all letters have the same length code

Not all codes are the same length: Number of Dots and/or Dashes (length of code) 1 Number of Possible Codes 21 = 2 2 22 = 4 3 23 = 8 4 24 = 16

Reasons for using codes of varying lengths • Most commonly occurring characters are given short codes • This is a form of file compression

Frequency Table for the English Language Spies can break simple codes that replace each letter with anothe symbol – just by counting the frequency of the symbols.

Zip File Compression • Eliminate Redundancy • Replace common words with short codes. • A table is created indicating short codes for common words.

More Binary Coding Schemes: • Braille uses raised or flat dots with six dot locations. • 26 or 64 unique codes are possible. Braille

Translating Braille

What about the humans?

We have ten fingers… Therefore we tend to use ten symbols for constructing numbers: 0123456789

Our numbering System is Arabic Indo-Arabic – of Indian 1. Positional - number Origin, introduced into the depends on digit’s west around 1000 A. D. position. 2. No Special symbol for the number ten. Hindu Numerals from 100 A. D. 3. Need for ZERO

How many apples are: 3, 674. 5 (in base-10) This is: 3 X 103 + 6 X 102 + 7 X 101 + 4 X 100 + 5 X 10 -1 3000 X 600 + 70 + 4 + 5/10

How many apples are: 3, 524. 5 if you happen to be a bird with six digits? (base-6) This is: 3 X 63 + 5 X 6 2 + 2 X 6 1 + 4 X 6 0 + 5 X 6 -1 = 3*216 X 5*36 + 12 + 4 + 5/6 = 648 + 180 + 12 + 4 + 5/6 = 844. 83

The Mayans used a base-20 numbering system

Computers have tiny electrical switches (transistors) that are controlled by two voltages 0000 0 0001 1 0010 2 0011 3 0100 4 0101 5 0110 6 0111 7 1000 8 1001 9 1010 A 1011 B 1100 C 1101 D 1110 E 1111 F • 28 = 256 • 216 = 65, 536 • 232 = 4, 294, 967, 296 A 32 -bit microprocessor can access 4 billion memory addresses – or 4 GBytes

Be a secret agent! • Using tic-tacs of multiple colors, devise a coding scheme for coding a sentence of about 15 -20 characters. • A sentence may have numbers and letters. • Determine how you will transport this code. • Keep codes as small as possible. • Can you memorize your codes?

Competition • Half of your team will code the message. • One person will transport the code to another room. • The other half of the team will decode the first message and code a response. • The first team to decode the 2 nd message has to eat all the tic-tacs!

How to construct numbers: The Roman Way I - one V - five X – ten L - fifty C - 100 (cento in Italian) D – 500 (diecicento) M – 1000 (mille) • 1945 = MCMXLV or MCMXXXXV ? or MCMVL ? • 1907 = MCMVII • 1909 = MCMIX Cumbersome to add, confusing to subtract. Very hard to multiply and divide.