The Atomic Pinball Clock was built long before there was any notion of building an exhibit. It was more of an exercise to learn how to use the popular Arduino microcontroller to put the orphaned backbox of a pinball machine back to good use. The design challenge was to use the existing sockets on the backbox, where the original pinball machine cabinet would have plugged in to the backbox, to manipulate the score reels and other available hardware to show the current time. The changes were meant to be reversible so that if an orphaned cabinet is ever found the added hardware could be removed and the backbox should still work in a pinball machine. An additional self imposed constraint was that the clock would need to be self setting so that it would not require being set to the right time when turned on nor batteries to keep the time when turned off.
The solution was to include a receiver for the WWVB time broadcast similar to those used by self setting clocks everywhere. The top level design has the Arduino board constantly monitoring the WWVB broadcast, decoding the current time, adjusting for the time zone (which is not included in the broadcast), converting the time to a sequence of pulses that change the score reels to the correct value, converting the pulses to the correct voltage and driving them in through the sockets at the bottom of the cabinet. In the end one modification was made to the original backbox wiring to add individual control to the chime so that it wouldn't chime each time the 1s score reel advanced. This modification also allows the clock to chime the hour at the top of each hour.
The original backglass for the backbox was in poor condition so it was scanned and cleaned up on the computer. The original design was faithfully restored except for a small modification to obscure the unnecessary 5th digit. The cleaned, revised version was printed on a sheet of plastic by a commercial printer.
The complete story of building the Atomic Pinball Clock with more photos is on the next page.