Alan Yates had always been fascinated with decadic dialing mechanisms. He also had been thinking about building a ring-counting Nixie or neon bulb clock. So when it came time to submit a project to the 555 Contest, he combined these interests along with 102 LM555 timers to build this decimal adding machine. The circuit includes 119 1N4148 diodes, 99 LEDs (90 Red and 9 Blue), dozens transistors, 353 resistors and 232 capacitors!
Architecturally the machine is a 9 decade accumulator adding machine with an indexing counter driving a multiplexer to simplify data input. It can do addition or subtraction using 9’s complement arithmetic and has optional carry-around. In a historical context it is an improved electronic implementation of the 1642 Pascaline.
The project was judged the winner of the 555 Contest in the “Complex” category. Congratulations Alan!