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Knock Knock Calculator | Make:
Knock Knock is a clever Arduino-controlled calculator toy, designed for small children. The user knocks out a calculation on the surface — addition, multiplication, subtraction, or division — and Knock Knock will spit back the solution, in the form of knocks, of course. It's a fun idea for a toy, but good luck trying to use this in secret during a "no calculators" test at school!