to detect a hit we use the following circuit.  because the hit is an impact and so happens very quickly, we include a capacitor to ensure that the voltage is still high enough to provide a logic level high when the C32 checks for the hit event.

the clock is implemented in .c code.  when the time is about to run out, in order to alert the player a led and buzzer are activated using the following circuits.

the 8 segment displays were the most exciting to implement.  a multiplexing shift register strategy is used so only 4 pins would be necessary to run all 16 of the led segments of the scoreboard.  every 100 times the code cycles, a refresh display function is called which turns off the display that is currently on, shifts in a new 8 bit character, and turns on the other display.  the code is so fast that the <50% duty cycle of the displays appears to be a constant glow to the naked eye.

unfortunately the displays are common cathode, which requires us to source 14 volts to each channel and so build 8 transistor circuits, one for each bit of an 8 segment display.  two more transistors were used to turn each display on or off.