Set input 1 to 1 or 0. Set inout 2 to 1 or 0. Click on the green flag. The circuit then outputs the sum and the carry out digit. The circuit is called a half-adder. After you reset the input sliders click the green flag. Test all possible inputs input 1 input 2 sum carry 0 0 0 0 1 0 1 0 0 1 1 0 1 1 0 1
In digital logic, a half-adder takes two binary digits (0 or 1) as inputs and outputs the sum digit and a carry digit. It's called a half-adder because it doesn't accept a carry-in digit. See Inside and note that the code consists of two Make a Blocks; one codes an XOR gate and he other an AND gate. George Stibitz (a research mathematician at Bell laboratories) built one of the first half-adders out of a soup can cut into strips to make switches (transistors are used as switches in modern digital devices) telephone relays, and a battery. It was called the K (for kitchen) computer. Once you have a half-adder, the next step is to design a full-adder that accepts a carry-in digit (0 or 1), outputs a sum digit (0 or 1), and outputs a carry-out digit (0 or 1). Align full-adders and you have a register. A full-adder is a bit more complicated. The full-adder I designed has 4 AND gates, 4 OR gates, and 1 NOT gate. Boolean algebra is the mathematical tool used to design logic circuits. The AND, OR, and NOT gates are built into Scratch (see green Operators) but I had to build the XOR gate used in this project.
