# Circuit scheme design: Display smaller number with 4 inputs (BCD 7seg)

Discussion in 'Homework Help' started by KSegu, May 13, 2018.

1. ### KSegu Thread Starter New Member

May 13, 2018
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Hello everyone, I'm trying to draw a circuit scheme.

What i know about the circuit:
It has 4 inputs (A,B,C,D) coded in BCD, and I want to show on display (7seg) the smaller number of this 4 inputs.

I have made this design, but I'm not sure that it works, specially the last part (4bit to 7seg).

2. ### dl324 AAC Fanatic!

Mar 30, 2015
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2,091
Welcome to AAC!
We only provide guidance for homework questions.
1. Label the inputs. I assume A and C, and B and D represent two two bit quantities, but it's unclear which bit is most significant.
2. Since you allow wires to cross, you should use connection dots to denote wire connections.
3. Post the complete text of the problem.

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3. ### KSegu Thread Starter New Member

May 13, 2018
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This is the complete text of the problem: "A,B,C and D are 4 BCD coded numbers. You want to show on display (7seg) the smaller number of the four." And they ask me to draw the circuit scheme.

I assume that A,B,C,D are 4 bits inputs.

And sorry for the wires, I'm using "circuits-cloud" and they are drawn like this

Thanks!

4. ### crutschow Expert

Mar 14, 2008
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6,768
Are you allowed to use a decoder?
What circuit elements are allowed?

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5. ### KSegu Thread Starter New Member

May 13, 2018
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Yes, a BCD-7seg decoder
Comparators, multiplexers and a BCD-7seg decoder.

Last edited: May 13, 2018
6. ### shteii01 AAC Fanatic!

Feb 19, 2010
4,667
745
So.
A is a 4 bit number, A0-A1-A2-A3 (you decide which is MSB and which is LSB)
B is a different 4 bit number, B0-B1-B2-B3
C is again a different 4 bit number, C0-C1-C2-C3
D is different 4 bit number from all the others, D0-D1-D2-D3

It sounds like you need to input all four numbers, compare them, find the lowest number, then display the lowest number on the 7 segment.

Your current schematic only shows one 4 bit number being inputted. The other three are missing completely.
The first step is to make a comparator.

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7. ### KSegu Thread Starter New Member

May 13, 2018
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Sorry, my bad, every input (A,B,C,D) is a 4 bit number, i should've specified.

8. ### dl324 AAC Fanatic!

Mar 30, 2015
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Show us an updated schematic.

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9. ### KSegu Thread Starter New Member

May 13, 2018
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This is what I meant to say

10. ### dl324 AAC Fanatic!

Mar 30, 2015
8,656
2,091
The comparator and decoder part looks okay. You didn't give a part number for the multiplexer, but that looks okay if a LOW selects the A inputs.

When using bussed signals on a schematic, you should show the individual signals entering or leaving a bus.

Here's an example from a homebrew EPROM programmer:

It uses "humps" for wire crossings, so connection dots aren't used. Drawing the ground symbol on it's side isn't recommended.

Last edited: May 13, 2018
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