In this circuit, three single digit displays have been interfaced with the Arduino serially. I used three 74595 ICs (Serial to Parallel Shift registers) to do this. The whole aim was to learn how to use these ICs.
Connecting them serially allowed me to use just one data wire, one clock wire, one control wire, and two supply wires. A great reduction from the 29 wires, otherwise required.
Code on Github: https://github.com/paramaggarwal/digitdisplay
Originally published at paramaggarwal.com.