# mini project

Discussion in 'Homework Help' started by gekides, Jan 27, 2013.

1. ### gekides Thread Starter New Member

Jan 27, 2013
5
0
i need help on how to start designing this circuit for my mini project. i am supposed to design a circuit that counts the number of '1's from the input A3, A2, A1, A0. show the number of '1's on the 7 segment display and the value of A on the 4 LEDS. the led will turn on when the display is 3 or 4

A3 A2 A1 A0 Display 1 Display 2 LED
(leds) (Display)

0 0 0 0 0 0 Off
0 0 0 1 1 1 Off
0 1 1 1 7 3 on

i have the expected waveform but i can't display it here so if needed i can email it

2. ### gekides Thread Starter New Member

Jan 27, 2013
5
0
i need help on how to start designing this circuit for my mini project. i am supposed to design a circuit that counts the number of '1's from the input A3, A2, A1, A0. show the number of '1's on the 7 segment display and the value of A on the 4 LEDS. the led will turn on when the display is 3 or 4

i have the expected waveform and the truth table but i can't display it here so if needed i can email it

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3. ### DickCappels Moderator

Aug 21, 2008
2,792
678
Can the circuit be sequential, or must it be purely combinational logic?

4. ### Salaja New Member

Jan 27, 2013
23
0
as for counting the '1's, a simple way to do this would be to use multiple adders. add the first 2 and the last 2 together, and you will then have 2 2-bit binary numbers (00, 01 or 10), which can then be added together to get the total number of '1's as a binary result, which could be as high as 100 (4) which means over all, you would need 2 2-bit adders, and 1 3-bit adder.

from there you can use simple logic gates to turn the led on if the result was '011' or '100' (3 or 4).

as for displaying it on a 7 segment display, you would have to use a 3-8 decoder, then a 7 segment display encoder (or equivalent logic circuit).

there are probably simpler ways, but this would be my solution.

-also this is my second post, so take everything i say with a grain of salt

5. ### gekides Thread Starter New Member

Jan 27, 2013
5
0
combination logic

6. ### gekides Thread Starter New Member

Jan 27, 2013
5
0
combinational logic

7. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
718
Is the answer supposed to be in discrete logic form, VHDL, or Verilog?

Post what you have so far in any of the cases.

8. ### WBahn Moderator

Mar 31, 2012
18,094
4,920
You say, "and the value of A on the 4 LEDS", but then talk like there is only a single LED. Which is it?

Is it safe to assume that you know how to display a three-bit binary value on a 7-segment display? If so, then you need to design a circuit that has four inputs (the four A_i signals) and three outputs (the three bits in the three-bit binary value). Take them one at a time as three separate design problems.

Are you familiar with Karnaugh maps?

9. ### gekides Thread Starter New Member

Jan 27, 2013
5
0
need 5 leds 4 leds to show the input and 1 leds to show when display 2 shows either 3 or 4

10. ### WBahn Moderator

Mar 31, 2012
18,094
4,920
For the 5th LED, you can look at the low three bits going to the (decoder for the) 2nd display and detect if that is either 3 or 4. You can leverage what you know about what it can't be in order to simply the circuit -- in fact, you can write it down by inspection. Hint: Are there any situations in which the third bit (the "4's" bit) is HI that you do NOT want the fifth LED to be on? Similarly, are they any situations in which the two low order bits are both on in which you do not want the fifth LED to be on?