Schematic Reference

Gym Agility: A Simple Strategy Game

This simple circuit is a two-person game of strategy and speed - and potentially, agility and athletic fitness. Each player has a row of four LEDs before him/her. Beside each LED, there is a push-button which, when pressed, lights up the corresponding LED. The aim of the game is for a player to illuminate all four of their LEDs in a row, in which case the circuit declares a winner. However, there is a catch. As soon as you light one of your own LEDs, the other player's corresponding LED goes out - and vice versa.

The game begins by giving each player two illuminated LEDs. Consider now that this game is scaled up and used in a gym. If the LEDs in the circuit are directly replaced with N-channel power MOSFETs, then 12V globes can be illuminated (a MOSFET's gate is wired in place of a LED's anode, the source goes to negative, and the load is wired between the drain and positive). If four large push-buttons are mounted on one wall and four on another, this could become a game of agility - if not a physical tussle to keep the other player away from critical push-buttons.


Here's how the circuit works:

Schmitt NAND gate IC1a and IC1b (4093) form a simple bistable latch. When one output (pin 3) goes "high", the other output (pin 4) goes "low" and vice versa. The main advantage of using a bistable latch (as opposed to a flipflop) is that it does not suffer from switch bounce. Four such bistable latches are fed to inputs A-D of IC2. However, for the sake of simplicity, only one of these is shown; ie, IC1a-IC1b. We now need to identify when all four bistable latches go either "high" or "low".

This is done using IC2, a 4067 16-channel multiplexer. When inputs A-D are all "low" (binary 0000), this opens decimal channel 0. Conversely, when all are "high" (binary 1111), this opens decimal channel 15. Channels 0 and 15 thus trigger a win for one side or the other, by taking pins 9 or 16 of IC2 "low". Finally, if the game is quite hectic, a win might only last for a fraction of a second before it is lost again. Therefore, IC1c and IC1d are wired as timers, which do not permit any further play until a win has been reported for one or two seconds - either via LED3 or LED4. During this time, however, the players' buttons may be pressed to reset the game to two LEDs all.