74HC00, 74HC191, 74HC4028
In this project, you re going to build a Russian roulette. If you hit the roulette, the speaker sounds. You have a hit probability of 1/4. You know the Russian roulette?
You're lucky that you get a sound instead of a bullet. Yes, you should be happy in failing the roulette. If silence relieved you, say to your friend, "It's your turn." (Of course, you can use the roulette for a guessing game.)
When you finish wiring, turn power ON. Dare to choose among the keys 2-5 and hold it down. Then, press the key S1.
This spins the counter, not the revolver. Release S1. The counter comes to a rest. If the rest status of the counter corresponds to the key you chose, the speaker sounds off until you release the key.
When S1 is pressed, a NAND multivibrator U1 "a" sends clock pulses to the up/down counter U3 where they are counted up.
The states of the Q0 and Q3 outputs of U3 are decoded by U4. For example, if the outputs of U3 is Q0 = Q1 = 1 when S1 is released, the output Q0 of U4 is 1.
Therefore, if S2 is the current selection, a NAND multivibrator U1 "c" oscillates and thus drives the speaker.