Name Date Period

← CS Unplugged

CS Unplugged activity

Secret Messages in Binary

About 20 minutesSoloPencil

Every letter’s ASCII code can be written in binary too: 8 boxes of 0s and 1s instead of one number. This sheet uses the same idea as Secret Messages in ASCII, just with a different way of writing the codes.

Your chart

Each binary code has 8 boxes. Left to right, the boxes are worth:

128   64   32   16   8   4   2   1

	A	B	C	D	E	F	G
Decimal	65	66	67	68	69	70	71
Binary
	H	I	J	K	L	M	N
Decimal	72	73	74	75	76	77	78
Binary						01001101
	O	P	Q	R	S	T	U
Decimal	79	80	81	82	83	84	85
Binary
	V	W	X	Y	Z	space
Decimal	86	87	88	89	90	32
Binary

One is done for you. Count forward or back from it.

What to do

1. Add up the place values wherever a code has a 1. That’s its decimal number.
2. Find that number in the chart and write the letter in the box under the code.
3. Write the binary code in the chart’s empty box, so next time you can just look it up.
4. Read your finished answer to check it makes sense.

Now decode these

1. A single 0 or 1 is called a ___.

01000010

01001001

01010100

2. Code that repeats itself is called a ___.

01001100

01001111

01001111

01010000

3. Underwater robots stay connected with a cable called a ___.

01010100

01000101

01010100

01001000

01000101

01010010

Now go the other way

Now go the other way. Add up the place values for each letter, then write its binary code, one bit per box.

R

O

V

Want the whole table, including lowercase letters? See the full ASCII / Hex table.

Answer key

1. BIT
2. LOOP
3. TETHER

Now go the other way: ROV → 01010010 01001111 01010110