Roulette with sound
This Project adds the dimension of sound to the decision-making process. It's also another good example of how different circuits can be joined together to make more complex devices.
Since the wiring for this Project gets a bit complicated, take your time when making the connections and double-check your work.
When you finish, turn power to ON. Press the Key and LEDs 1, 2,3, and 4 will begin to flash one after the other. You'll also hear a sound from the Speaker each time a LED lights.
Now release the Key. The LED flashing will begin to "slow down" as will the sound from the Speaker. Eventually only one LED will be lit out of the four. You probably recognized the multivibrator circuit in the schematic quickly. Its output goes to the digital portion of the circuit, made up of the flip-flops and the NAND gates.
These circuits make up a counter that lights each LED in turn and also drives the audio oscillator section. This is why you hear sound each time one of the LEDs lights.
Take a good look at how the two flip-flops are connected. Notice how the Q output of one flip-flop serves as the clock for the second input. A flip-flop can't change to reset or set unless the clock signal is input, even if the other two inputs change.
Now think about that a minute while examining the possible outputs of the two flip-flops. Look at how those outputs are combined in the NAND gates. Does this give you any clue about how a counter "counts" like it does?
Be sure to make a note about what you think — we'll see later how close you come to the truth.