This weekend I made a prototype digit unit with wiring for segments mostly as described in log entry #2.

Segment selection done with two-position switches, and digit select is done with push-button switch. In full-scale implementation instead of switches there will be logic gates.

From initial measurements of current flowing through segments I think there should be another powering scheme, because total current through all 7 segments only about twice as much as current flowing through one segment, when it is the only one selected. I suppose I should use different voltages for logic and for display. Also there have to be some adjustments to wiring to accommodate the changes.