Make: More Electronics

Chapter 20. Experiment 20: Decoding Rock, Paper, Scissors

I invite you to inspect Figure 20-1. This circuit is the simplest way I could find to create a fully-featured version of the Rock, Paper, Scissors game, using two decoders to simplify the logic while retaining switches to activate the LEDs and a beeper. Because it uses switches as well as logic gates, you can think of it as a hybrid circuit.

The Logic

I’ll deal with the logic first. You’ll remember that at the end of Experiment 17, I decided that logic gates were inconvenient and complicated for the task of detecting if either player had cheated. Well, this difficulty has now disappeared.

In the schematic, each switch now has a binary-code place value of 1, 2, or 4, and each set of three ...