Quick draw game III
Electronic
74HC00, 74HC02, 74HC191

Here's a game circuit with two switches; two players compete to be the first press of the key.

Which key is pressed first is indicated by the rotation direction (clockwise or counterclockwise) of the display.

See the schematic. S1 and S2 in block A are the keys for the two players.

IC 74HC191 is a 4-bit up/down counter. It works as an up or down counter, depending on which key is pressed first. (Don't worry, we'll explain you more about this IC later.)

The output of IC is sent out from Q0 and Q1 and applied to the block B, which is what is known as decoder. Can you guess how it got this name? (Do you suppose it could have anything with to do with "decoding" the output of the counter?)

The output of the decoder is sent to the LED display in block C.

Assemble the project, turn power ON, and see what happens to the LED display when you repeatedly turn S1 ON and OFF. Do you see the display on the LED display turning clockwise?

Now repeat turning S2 ON and OFF, and the display turns counterclockwise.

Now you can play the game with a friend. Tell him to choose his switch and press it at a "Go" sign. If your key is S1 and you pressed and released it faster than he did his (S2), the display turns clockwise, and that means you've won the game.