I built this circuit in order to attend a project where I would have to "tell" a 3D Cartesian CNC Robot witch cell of a 3X3 empty matrix it had to write a circle. Controlled by Arduino, the mini CNC was able to play tic tac toe and it's symbol was the X mark. The problem was that I didn't have enough digital IOs in Arduino to detect each of the nine push button presses and control the other CNC's digital functions needed, so I decided to draw and build this circuit where I was able to represent up to 15 push button presses with only 4 outputs, and that worked. I used 3 X 7432 CIs to achieve this goal. I attached other two push buttons, one to set the machine's difficult and other to draw the hash matrix to initialize the game. Here I represent only 9 push buttons in line. Pressing them (rising from right to left) gives a binary representation of it's position at the outputs.
