Discussion in 'Homework Help' started by xdone, Jun 16, 2010.

1. ### xdone Thread Starter New Member

Jun 16, 2010
9
0
As mention i am given 4 Inputs D C B A and the decoder for outputs for common cathode a b c d e f g.
I need to obtain from 0-9, A-F
So the truth table which i obtained is
D C B A| a b c d e f g
0 0 0 0 |1 1 1 1 1 1 0
....
....

So i made a k map for each segment and how am i suppose to implement the circuit using only basic gates?
this is what i obtain
a = BA'+ DC'B'+DA'+D'B+CB+D'CA+C'B'A' (' means invert)
b = D'C'+D'B'A'+C'B'+D'BA+C'BA'+DB'A
c = ....
d= ....

2. ### Georacer Moderator

Nov 25, 2009
5,151
1,266
I take it your question is about the sheer number of the materials used. Do the restrictions of your exercise prohibit you from using a ready-made bin-to-7seg decoder? If so, consider using groups of gates more than once, ie construct the CB combination needed for a and invert it to use it for the b segment. Or try to find suitable factorizations among the sum elements that can be used by multiple segments.

3. ### xdone Thread Starter New Member

Jun 16, 2010
9
0
Do i combine the segments a b c d e f g together?

Apr 5, 2008
15,799
2,386
Hello,

Just take a look at the datasheet of the 7447 how it works.

Bertus

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5. ### xdone Thread Starter New Member

Jun 16, 2010
9
0
so sorry, i dont get what u mean by the 7447.

Apr 5, 2008
15,799
2,386
Hello,

Read the attached PDF in my last post.
It says sn54ls47, but it equals the 7447.

Bertus

7. ### xdone Thread Starter New Member

Jun 16, 2010
9
0
sorry bertus for asking again, so after getting all the segments individually, do i combine them first? i used K-map method to simplify them already.

8. ### xdone Thread Starter New Member

Jun 16, 2010
9
0
Sorry guys, after getting each segment, must i combine them together? i need help urgently sorry.

9. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
If you look at the data sheet for any 7 segment display, you will see that the above signals control individual segment illumination.

10. ### xdone Thread Starter New Member

Jun 16, 2010
9
0
so i dont combine them? then how am i suppose to implement the circuit?

11. ### n1ist Active Member

Mar 8, 2009
171
16
Think of your circuit as a black box that has 4 inputs and 7 outputs. There's no combining of the segment outputs.

Look at the pdf that Bertus linked to above. They have the internal logic diagram for the 74ls47, which is a bcd-7seg decoder. You just need to change it a bit to display a-f instead of the random symbols it does now.
/mike

12. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
Try looking at a display and the segment control lines. It becomes very obvious how the decoder/driver and the display function together.

13. ### xdone Thread Starter New Member

Jun 16, 2010
9
0
In other words, i implement the circuit seperately then later combine them? Wow, it will be messy hahas

14. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
As an exercise, just draw up a schematic that shows the various connections.

15. ### xdone Thread Starter New Member

Jun 16, 2010
9
0
sorry, what do u mean?

Apr 20, 2004
15,815
283
17. ### xdone Thread Starter New Member

Jun 16, 2010
9
0
but i am required to draw the digram with basic gates =/

18. ### Georacer Moderator

Nov 25, 2009
5,151
1,266
Exactly! The datasheet of the 7447 contains a schematic wich is down to the gate level. You could duplicate the exact behaviour of the IC by constructing the gate circuit given. If you want to display A, B, C, etc for numbers larger than 9 however, you need to modify this circuit, wich, I imagine, will require some work, but isn't impossible by any means.