Close-in II
555, 74HC00, 74HC76

This is a project that's a bit different from the last few: This one too helps you make a decision... like whether to go to the left or right.

After you finish the wiring connections, turn power ON.

You notice that LED 4 lights up.

Now press S1. You see LEDs 2, 3, 5 and 6 light at what seems to be "half brightness".

Now release S1. What happens?

You see LED 4 and one more LED lights up. Which one was it?

Now press and release the key.....and try it again.....and again. Does a different LED light up each time or does the same one light up over and over?

Look at the schematic. You notice that LED 4 is a separate circuit of its own, not affected by the rest of the project. That's why LED 4 stays on all the time.

The rest of the project is the oscillator U1/counter/decoder arrangement we've seen in other projects. Again, can you figure out how the outputs of the flip-flop are combined in the NAND gates to light just one of the LEDs? Be sure to make a note of your guess.

You can also use this project in game. The winner could be whoever can get a LED to light closest to LED 4, for example.








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