Experiment 21: Race to Place

Chapter Experiment 21: Race to Place

Make Electronics Book Learning by Discovery
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Make Electronics Book Learning by Discovery

  • Chips, Ahoy!205Experiment 21: Race to PlaceExperiment 21: Race to PlaceThe next project is going to get us deeper into the concept of feedback, where the output is piped back to affect the input—in this case, blocking it. It’s a small project, but quite subtle, and the concepts will be useful to you in the future.You will need:• 74HC32 chip containing four OR gates. Quantity: 1.• 555 timers. Quantity: 2.• SPDT switch. Quantity: 1.• SPST tactile switches. Quantity: 2.• Various resistors.• 5V supply using power regulator as before.TheGoalOn quiz shows such as Jeopardy, contestants race to answer each question. The first person who hits his answer button automatically locks out the other contestants, so that their buttons become inactive. How can we make a circuit that will do the same thing?If you search online, you’ll find several hobby sites where other people have suggested circuits to work this way, but they lack some features that I think are necessary. The approach I’m going to use here is both simpler and more elabo-rate. It’s simpler because it has a very low chip count, but it’s more elaborate in that it incorporates “quizmaster control” to make a more realistic game.I’ll suggest some initial ideas for a two-player version. After I develop that idea, I’ll show how it could be expanded to four or even more players.AConceptualExperimentI want to show how this kind of project grows from an idea to the finished version. By going through the steps of developing a circuit, I’m hoping I may inspire you to develop ideas of your own in the future, which is much more valuable than just replicating someone else’s work. So join me in a conceptual experiment, thinking our way from a problem to a solution.First consider the basic concept: two people have two buttons, and whoever goes first locks out the other person. I always find it helps me to visualize this kind of thing if I draw a sketch, so that’s where I’ll begin. In Figure 4-87, the signal from each button passes through a component that I’ll call a “button blocker,” activated by the other person’s button. I’m not exactly sure what the button blocker will be or how it will work, yet. Now that I’m looking at it, I see a problem here. If I want to expand this to three players, it will get complicated, because each player must activate the “button blockers” of two opponents. Figure 4-88 shows this. And if I have four players, it’s going to get even more complicated. Anytime I see this kind of complexity, I think there has to be a better way.ButtonBlockerButtonBlockerFigure 4-87. The basic concept of the quiz project is that the output from one button should feed back to intercept the output of another button. At this point, the way in which the “button blocker” circuit works has not been figured out.