If you're interested, I hope to post a single chip Charlieplexed Clock based on the experiment below in the Projects sub-forum this weekend.
The first installment is just the Clock portion of the experiment below and the source is written using the free/lite version of BoostC. Features include;
<> run and set modes (a display 'group' flashes at 2 Hz in set mode)
<> switch debouce (press and release states)
<> switch press beep feedback
Subsequent installments will include the Calendar, Alarm, and (appliance) Timer functions using the same base hardware (PIC, six digit display, four switches, etc.) as I finish moving the code over from assembly language to C.
Please note that the drawing is misleading in that the displays are wired in a Charlieplexed matrix even though the drawing suggests they're wired as a standard multiplexed matrix. I'm working on a new drawing.
Regards, Mike