Strange LED display

[electronicjo]

I've managed to salvage a LED board(4 seperate 8-seg displays on one
board with a simple 12 pin connector) from an old microwave hoping to
use it in my own application. Apparently, this board has a strange
design that is difficult to understand:
http://home.comcast.net/~electronicjo/display.gif
The two components between the pair of LED displays are normal LEDs.

Some things to note:

1.) 5V - Pins 1 through 4(from left to right on PCB connector) are
"Display select". When any of these pins are connected to 5V, the
corresponding display will light up when the pins from Note 2 are
grounded.

2.) GND - Pins 5 through 11 control exactly which LED segment bars
will light up. Also note in the diagram that each segment is
connected to the next displays' corresponding segment.

3.) Pin 12 of the connector is the common cathode of the two regular
LEDs and will only light when Pin 3 is high.

Now obviously the problem is this: How can each display have different
numeral values if each segment from each display is interconnected?
The only solution I can think of is quickly switching each display
with a number accordingly so that is appears to have different
values. Unfortunately, the main board of the microwave with all the
circuitry is damaged, so attempting to analyze that won't work(and
also the ICs are antique).

Any comments appreciated.

 

[Rich Grise]

Now obviously the problem is this: How can each display have different
numeral values if each segment from each display is interconnected?

The only solution I can think of is quickly switching each display
with a number accordingly so that is appears to have different
values.

Yes, that's precisely correct. (I presume you've verified that the
segments actually _are_ LEDs). It's called "multiplexing." The program
would set up what the segments are supposed to be, then send the
segment information for one digit, and simultaneously activate that
digit, for a little while. Then, turn it off, and send the segments
for the next digit, turn it on, and so on. This happens faster than
you can see the flicker, so they look steady.

Hope this helps!
Rich

 

[Quack]

Not strange at all, but completely normal.

You have to scan 1 digit at a time, so only 1 is on at any one time,
but fast enough that your eye wont ever see any digit turn off
(googleersistance of vision).

You will need to interface it to some form of micro-controller and
have a play around, you will find many examples searching google of
how to use these.

Alex.