[Andrew] built this pong clock over the span of a couple of days. The PIC 18f2520 he used can serve as a real time clock with the addition of an external clock crystal. His project proves the usefulness of an oscilloscope as poor board layout caused interference in the crystal connections, something difficult to troubleshoot without this handy lab tool.
Pong clocks have been quite popular. This one is nice because it’s easy to throw together now that [Andrew's] done the coding work for you. Written in assembly, reading and understanding his code might be a good exercise if your low-level language skills are lacking.