Figure 4.3
shows a circuit for each contestant of a quiz master used to identify the
first contestant to push his or her answer button in a quiz game. Each
contestant has a push-button and an indicator light. The light of the first
person to answer should come and stay on. At the same time all other lights
should be prevented from coming on.
Figure 4.3:
The circuit for each contestant of a quiz master
The numbers in Figure
4.3 are the pin numbers if a 74LS00 I.C. (Quad 2-input NAND gate) is
used. However, the circuit is only suitable in a quiz master for two
contestants. When there are 4 contestants,
we have to replace the 2-input NAND
gate with the input A by a 4-input NAND gate such as the 74LS20 (Dual
4-input NAND gate).
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