I have just spent a bit of time reverse engineering the displays I have acquired for my archery timer.
In Archery events sometimes we shoot 'details' or pairs of archers on the same target. Pair AB followed by CD.
This is indicated on the timing lights for clarification of the archers turn at the target.
Well given these are powered off a CD4511 BCD to seven segment display controller you could imagine my surprise when I found that the segment outputs from the 4511 did not match up with the segments in the display.
THEN I noted that the series resistors were not all the same value even though all LED strings consisted of 5 LEDS. No this was interesting. Tracing through a few more bits of the circuits and I found that there were several segments of both displays common - mmmmm.
Ok different approach needed. I then looked at the control signals of the 4511 and found only 2 lines were in use. The BL input obviously to blank the display when not shooting in pars and ONE - YES only one data line attached to the C bit input.
I then looked at the logic states of the outputs when this input is active or not and it all started to drop into place.
A and B as seven segment displays use all the segments apart from the D segment on the A display.
From the truth table you can see if we ONLY make input 'c' low we get ONE segment turned off (an it's segment G) all others would be on.
This would display the AB on the two seven segment displays
Now we take the instance of input 'c' being high
We now have a total of 3 segments off. Which in my displays would be segment b & c on one display and g on the other to give an indication of CD.
Took a while for me to get my head around this non standard but very clever use of the humble 4511 device.
I take my hat off to the original designers - cunning lads.
So there you go, don't always assume the device is being used as documented in the data sheets. Someone with a devious mind may have been there before you!.