Batch 3 - Class 115 - Building a Dominos Computer

• If you could choose the shapes, can you get area occupied by each shape equal?

• Primer for Binary Numbers
• Explain what binary numbers are - Reference Class 2

  Lets count binary - Get 5 people to stand in a row with cards numbered 1 (and reverse side being 0), and ask them to count. Rules of counting same as decimal system, but now 10 replaces by 2Person at the left most position always increments his card (after 1, comes 0)Any person after that increments their card when the card to the left goes to 0Notion of units, twos, fours, eights, sixteens place. The number formed at any point is units place, plus 2 times twos place, plus 4 times fours place and so on5 people can count to 2^5, and so on
• Exercise: Give each kid a number that they must write using binary notation
• Primer for Logic 
• Introduce OR, AND, XOR Gates

  Draw Truth Tables for each
• How would you create OR Gate using dominos (explain the notion, that in an OR gate, the "output" gate should fall if either or both of the input gates fall)

• How would you create an AND Gate using dominos
• Note that we may need a mechanism by which one domino knocks over the output, but then modify it so that it gets blocked unless the second one is also knocked...

• How would you create an XOR Gate using dominos (explain XOR Gate)
• Note that what we want is that either of the inputs knocks over the output, but they block each other if they are simultaneously knocked over - so lets take an OR gate as a base, and then insert a blocker there

• What has all of this got to do with adding numbers?
• Lets draw the truth table for addition (half adder actually) - Note that we have two bit output now
• Note that it has an XOR Gate, and then if both dominos are knocked, then we want the second bit to fall over (like an AND gate). Can we think of combining the XOR and AND logic above to create this adder?
• 
• Is this enough - have we covered all scenarios to do addition of larger numbers?
• What if we were doing 3+3 - what other capability do we need?
• Full adder - we need a way to add 3 numbers to incorporate carry

  But that is simple because we can just add two numbers and then add the third number to those
• If we have a full adder, we can then put them next to each other to create multi-bit adders
• Lets see some videos
• https://www.youtube.com/watch?v=lNuPy-r1GuQ - Start at 8 mins and end at 11 mins
• https://www.youtube.com/watch?annotation_id=annotation_663981515&feature=iv&src_vid=lNuPy-r1GuQ&v=OpLU__bhu2w - Start at 3:30 and end at 5 mins

• Answer: 7 (Total fish in tanks will be 39 in 13 tanks)