Experiment 21: Race to Place
206 Chapter 4
Also, there’s another problem. After a player lets his finger off the button, the
other players’ buttons will be unblocked again. I need a latch to hold the signal
from the first player’s button and continue to block the other players.Button
BlockerButton
BlockerButton
BlockerFigure 4-88. The quiz concept becomes more complicated when an additional pushbutton
is added. Now each button must block two other buttons. If a fourth button is added, the
circuit will become unmanageably complex. There has to be a better way.This now sounds even more complicated. But wait a minute, if I have a latch
which allows the winning player to take his finger off his button, I don’t care if
any of the buttons are being pressed anymore—including the button of the
winning player. As soon as his signal is latched, all the buttons can be blocked.
This makes things much simpler. I can summarize it as a sequence of events:- First player presses his button.
- The signal is latched.
- The latched signal feeds back and blocks all the buttons.
The new sketch in Figure 4-89 shows this. Now the configuration is modular,
and can be expanded to almost any number of players, just by adding more
modules.
There’s something important missing, though: a reset switch, to put the sys-
tem back to its starting mode after the players have had time to press their
buttons and see who won. Also, I need a way to prevent players from pressing
their buttons too soon, before the quizmaster has finished asking the ques-
tion. Maybe I can combine this function in just one switch, which will be under
the quizmaster’s control. In its Reset position, the switch can reset the system
and remove power to the buttons. In its Play position, the switch stops hold-
ing the system in reset mode, and provides power to the buttons. Figure 4-90
shows this. I’ve gone back to showing just two players, to minimize the clutter
of lines and boxes, but the concept is still easily expandable.