Here it is: MonoPong involves a CMOS NAND Gate (4011), a 4510 up/down decade counter, 4028 BCD to decimal decoder chip and as an oscillator an NE555 in astable mode.
is a 1D-version of the famous PONG game. The "ball" moves from left to right. The player has to push the button at the right moment to strike it back. If he misses the "ball" the other player wins one point.
Step 1: How it works
IC2 in the schematic is a CMOS 4510 up/down counter. Driven by IC1 which is a NE555 in astable mode it counts from 0 to 9 in BCD code. Normally it counts from 0 to 9, but it can be switched to count in the opposite direction by b setting pin 10 to HIGH.The BCD code is converted into a decimal code by the CMOS 4028 (IC2). This one drives the display and gives out the counted number in form of one of 10 LEDs lighting up.
The last IC is a 4011 NAND gate. Two of the NAND gates are connected to work as a RS flip flop. The inputs of the other two NAND gates are connected to the buttons and LED1 or LED10. The outputs are connected to the RS flip flop. If you push the button at the right moment, which means for example when LED10 lights up, the output of the NAND gate sends a LOW signal to the flip flop which changes its output state (eg. from HIGH to LOW or vice versa). This signal goes to pin 10 of the 4510 to change the direction of the count. The "ball" bounces back.