Stop the seven
Electronic
LM324, 74HC00, 74HC02, 74HC191, 74HC4511

In this project, you're going to make a slot machine for a game called "Stop the Seven." The visual indicator cycles through 0 - 9, so press a key for the short moment when 7 is displayed. If you did it right, number 7 stays lit. You'll be rewarded with a monotone—sorry, not money.

When you finish wiring, turn power ON and press the start key S2.

You'll hear the speaker zipping and see the LED display changing numbers "0 - 9, 0 - 9, ...."

Press the stop key S1 to hit "7." If you shot "7," a monotone sounds. If you miss it, the number you shot (say "6") remains on the LED display, and the game is over.

Press the start key S2 to restart the game. U2B is an oscillator to change the display indication, while U2B is another oscillator used to generate a sound.

When S2 is pressed, the R-S flip-flop U1 "a" is set and U2B is put into oscillation. In response to this oscillation, the decimal counter U3 counts up to change the display indication "0 - 9, 0 - 9....."

As far as U2B is H, U2B oscillates to produce an intermittent sound. When S1 is pressed, the R-S flip-flop is reset, and the number held in U3 at that moment begins to stay on the display.

If this displayed number is 7, the output of U1 "b" changes to H, so U2B oscillate to sound a monotone.