So I am trying to understand the wiring on the basis 3 to the 7 sea display.
The display on this board appears to have a common anode for each of the 4 segment displays ok cool no problem there

However, it appears that the cathode of display is also common. So sinking the cathode on one sinks the cathode of the other.
How is is then possible to to have a different number on one segment verse another.
The common anode will allow you to shut one whole segment on or off but how is it possible to ever have a different number on the 4 displays

no understanding this? for example say to went segment A on display 1 on and segment B on display 2 on but not segment A on display 2

 

This type of display works by strobing.

 

Take a look at this. https://en.wikipedia.org/wiki/Multiplexed_display

 

apparently things have changed since I was in college! lol thanks all

 

apparently things have changed since I was in college! lol thanks all

Multiplexing 7-segment displays have been around since 7-segment displays were invented more than 50 years ago.

 

Maybe he’s like me, and went to college more than 50 years ago!

Bob