A single display has seven segments which can be put together to form any number from 0 to 9 (ignore letters for now).
if a decoder is attached directly across to the display as seen in the diagram above, then any number can be formed just by putting 4 letters together as follows (ABCD as seen on the left of the decoder). They are attached to four individual voltage inputs at the bottom.
A will display 1 when a voltage is put to it.
B 2
A B 3
C 4
A C 5
B C 6
A B C 7
D 8
A D 9
all off 0
Call the four Voltage inputs in the working diagram A B C D from left to right at the bottom, then alter any of those four.
If a V is 3.6 V or above then it is an active HIGH.
If a V is below 3.6 V then it is considered off as LOW.
Example:
Alter the four voltage inputs at the bottom so that only A and C are HIGH with their green lights on bright.
From the table here you can see that number 5 should be on the display.
When you have had some good practice with this then you will realise that a logic high source is something which does that voltage alteration for you.....but that is for another day to use.
