Shot in the dark IV
Electronic
555, 74HC00, 74HC191, 74HC4511

In this project, you can be a gunman in a western film. You'll be starring in "Midnight" rather than "High Noon." And, instead of a gun, put a flash lamp in your holster.

When you finish wiring, turn power ON.

Before starting the game, make the room dark. Press S1 just for a moment. LED 1 lights a little later. In no time, shoot your flash lamp at the CdS cell. The time it took from lighting of LED 1 to hitting of light on the CdS cell is indicated by a number "1 - 9" on the LED display. The smaller the number, the more responsive your reflex nerve.

The control volume adjusts the light receiving sensitivity of the CdS cell. When the control volume is rotated more counterclockwise, the circuit can responds to weaker light. If the number you get is almost always "1" or "2", adjust R5 and C2 for smaller values.

When S1 is pressed, C3 begins to discharge, and when the voltage at C3 exceeds the threshold of U5, Q2 turns ON and LED 1 lights.

At the same time, the counter U3 receives clock pulses from the oscillator U2 and counts up from "0." When a light beam hits the CdS cell, the J-K flip-flop U1 is set and the counter stops operation.

The value of the counter is decoded by U4 and indicated on the LED display. The counter also stops operation when it has counted up to "9."