说明：  no intro
(1, design a circuit can be a tug of war game. 2, the circuit using the 15 (or 9) light-emitting diodes, only after the middle of a bright start, namely the center of a tug of war. 3, games, and each side holding a button, rapidly and constantly pressed to produce pulses, who according to fast, to whom the direction of bright spots on the move, every time, bright spots move once. 4, highlights the terminal diode when the move to either party, the party would win, this time the two sides had no role in the button, the output to maintain, and only reset after so bright to restore to the center. 5, digital tube display the number of the winner of the plate. Teaching tips: 1, buttons, signals that the input pulse signal, every time I press the button should be able to effectively count. 2, with reversible counter to add, subtract count input pulse signal, respectively to accept two-way, reversible, the original output of the counter state 0000, via decoder output, so that the middle of an L)