# two 7 segments displays

Discussion in 'Homework Help' started by garcon, Feb 8, 2014.

1. ### garcon Thread Starter Member

Jan 3, 2014
33
0
Dear all,
I have an assignemnt that asks lot of things and as a new guy for the lectronics circuits, some time I lost and some times when I get some help, I can speed up my understanding on this subject.

Here is the problem:
Here is the principle of a 7 segment Display.

We consider each module of the 7 segment displays disposes 4 bits in entry and function according to the following principles.

The binary numbers between 0000 and 1001 display the corresponding numbers.
The binary value 1111 displays the symbol "-" (represent the minus sign)
The other binary values will switch off the displayer (values 1010, 1011, 1100, 1101,1110)

a)- create the truth table: I did this part so ok.
b)- using k-maps do a boolean expression for output a & g: done also.
c)-Now by using a 2 displayers 7 segments and by re-using the above one, you should conceive a modular block of signed 5 bits in entry(2's complement).
When the entry value is a negative number, the first displayer will display "-" minus sign. and the second displayer the number.
Note: we will limit the value in entry in such a way that if the number to display is less than -9 (-10, -11, -12 etc), we display -9 (first displayer "-" and second 9).
If the value to display is higher than 9 (10, 11, 12 etc), we display 9 (first displayer off and second displayer 9).

Question:
Explain in English the steps to be used to resolve this problem.

-You are asked to give a solution for this problem by using (ALU, Additionner, subtractor, comparater, Multiplexer)

- you should consider a numeric thermostat to control the temperature of a room. A heating system or climatization can be controlled accordingt he following cases.

-The system can measure the temperature of a room between 0 and 31 degrees with precision 1 degree.
A rotative button will allow to give the temperature that needed. The introduced temperature will be between 0 and 31 degree with precision 1 degree.

The system disposes a two 7 segments displayers that allow to to indicate the difference in temperature between the advised and the measure one. The display values will be between -9 and +9.
The first 7 segment displayer will either be off or will display the sign "-"

According to the difference in temperature to correct, the thermostat will control the system of heating or climatization hence:-

-if the difference in temperature is nul, the ventilation is cut.
-if the difference in temperature is between -1 and +1, the ventilation is activated but heating and climatisation is disabled.

-if the difference in temperature is higher than -2 or +2, the ventilation is active.

soit le chau age ou la climatisation est activee selon le cas (ethier heater or ventilation is active according to the case.)

-Identify the entry and output of the system, the number of bits per entry and suggest a codage for the different bus used in entry et output.

-using the complex blocks seen in the class, suggest a solution to the thermostat problem in a schematic way. Integrate the block in your displays.
No need to rewrite the detail, just uniquely the representation.

This is the problematic which I am trying to do but very complicated for me to advance.

I thank you

2. ### MrChips Moderator

Oct 2, 2009
12,648
3,458
Bienvenue to All About Circuits. Hope you have an extended stay and that you find the threads and discussions very useful.

The purpose of Homework Help is to assist students in obtaining a better understanding of the assignment or topic at hand. We do not do your homework for you.

Here are some guidelines for requesting Homework Help.

In short, show us your work and what you have accomplished so far and then ask a specific question and we will try to provide help.

3. ### WBahn Moderator

Mar 31, 2012
18,089
4,917
Don't try to tackle everything at once. Break it down into small chucks (and the problem itself is trying to lead you toward that approach).

So focus on one aspect of the problem and show your thoughts and best effort on that aspect. We can then help you find your way to a workable solution for that aspect and then we can all move on to the next.

4. ### garcon Thread Starter Member

Jan 3, 2014
33
0
Thank you.

Here is what I did so far...
These are for questions a and b for truth table and boolean expression for a & g.
please give me some hint on how to tacle the two 7-segments displays. at least representation.
..
Dec Inputs outputs
w x y z a b c d e f g
0 0 0 0 0 1 1 1 1 1 1 0
1 0 0 0 1 0 1 1 0 0 0 0
2 0 0 1 0 1 1 0 1 1 0 1
3 0 0 1 1 1 1 1 1 0 0 1
4 0 1 0 0 0 1 1 0 0 1 1
5 0 1 0 1 1 0 1 1 0 1 1
6 0 1 1 0 0 0 1 1 1 1 1
7 0 1 1 1 1 1 1 0 0 0 0
8 1 0 0 0 1 1 1 1 1 1 1
9 1 0 0 1 1 1 1 1 0 1 1
10 1 0 1 0 x x x x x x x
11 1 0 1 1 x x x x x x x
12 1 1 0 0 x x x x x x x
13 1 1 0 1 x x x x x x x
14 1 1 1 0 x x x x x x x
15 1 1 1 1 x x x x x x 1

k-maps for a)

00 01 11 10
00 1 0 1 1
01 0 1 1 0
11 x x x x
10 1 1 x x
A=xz+wy’+w’x’y+w’x’z’

For g)
00 01 11 10
00 0 0 1 1
01 1 1 0 1
11 x x 1 x
10 1 1 x x
G=w+xy’+w’yz’+w’x’y

Many thanks

5. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,515
515
Ok, you are using wxyz for the four bits that represent numbers 0-9. I think you need a fifth bit, this fifth bit will be the sign bit for the second 7 segment display that shows negative sign.
 v w x y z 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0

and so on.

The v bit will control the second 7 segment display, the need for minus sign.

Last edited: Feb 9, 2014
6. ### garcon Thread Starter Member

Jan 3, 2014
33
0
Thanks.
yes, w x y z are for the 4 bits entry.
As explained in the problem,
0000-1001 is used to display 0 to 9.
1010 -1110: xxxx means used to off.
1111: is to display "-"
Do you mean I need to do another truth table with 5 bits entry?
like w x y z p?

and how this could be represented using decoders?

thnak you so much

7. ### garcon Thread Starter Member

Jan 3, 2014
33
0
Is the V bit entry all 0?
and the other w x y z remains as done before or does v changes?
tks

8. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,515
515
No, since v bit is first on the left, half of v bits will be 0, the other half will be 1. So when v bit is 0 and wxyz are from 0000-1001, you have positive numbers from 0 to 9. When v bit is 1 and wxyz are from 0001-1001, you have -1 to -9.

9. ### WBahn Moderator

Mar 31, 2012
18,089
4,917
One thing you need to note is that the value you are trying to display is represented as a two-complement integer. So think of your system as a couple of black boxes. One box generates and outputs the set point temperature. One box measures and outputs the actual temperature. One box outputs the difference temperature. One box outputs the signals to the two 7-segment displays.

Can you sketch a system diagram than integrates these boxes together and describes the signals between them? For each interconnect, indicate how many signal lines are needed, what the values that can be expected are, and how those values are represented.

10. ### WBahn Moderator

Mar 31, 2012
18,089
4,917
No. When v is 1 the wxyz do not map as you've indicated. The instructions explicitly state that the value is represented in two's complement.

11. ### garcon Thread Starter Member

Jan 3, 2014
33
0
I tried to complete the truth table with 5 bits entry.
The negative bits are in 2's complement.
dec v W X Y z
0 0 0 0 0 0
1 0 0 0 0 1
2 0 0 0 1 0
3 0 0 0 1 1
4 0 0 1 0 0
5 0 0 1 0 1
6 0 0 1 1 0
7 0 0 1 1 1
8 0 1 0 0 0
9 0 1 0 0 1
-1 1 1 1 1 1
-2 1 1 1 1 0
-3 1 1 1 0 1
-4 1 1 1 0 0
-5 1 1 0 1 1
-6 1 1 0 1 0
-7 1 1 0 0 1
-8 1 1 0 0 0
-9 1 0 1 1 1

12. ### WBahn Moderator

Mar 31, 2012
18,089
4,917
I would suggest that next you do what I suggested in Post #9.

Once you have that, then we can focus on the last box that is described and try to break it down into two or three sub-boxes. Along the way, it will be come trivially obvious what a given box has to do and how to implement it with the list of components you were given.

The goal is to take a big problem that is overwhelming when considered as a whole and break it into smaller and smaller problems until you get to ones that you can solve readily.

13. ### garcon Thread Starter Member

Jan 3, 2014
33
0
Honnestly speaking, I need your help a bit more to have a clear idea where to start to tackle this problematic.

I have try to design and implement lot of possibilities but don't convinced by my try.

Could you give me some hints please?.....

Much appreciate

Thanks

Last edited: Feb 9, 2014
14. ### garcon Thread Starter Member

Jan 3, 2014
33
0
I just back few minutes ago from my student weekend work and I was not able to follow up on post 9.
can any one online can help me please?

15. ### WBahn Moderator

Mar 31, 2012
18,089
4,917
I described four specific boxes for you to use as building blocks. Are you saying that you can't even TRY to draw a diagram that takes those four boxes and connects them up in a reasonable way? I'm not even insisting that you get it right, but you seem to be saying that it is unreasonable to expect you even to make an attempt.

16. ### garcon Thread Starter Member

Jan 3, 2014
33
0
I have tried to sketch but as I am not sure, I prefer to ask few more hints.

Here is what I tried, as you mention 4 boxes.
box1 and box2 (set temp., actual temp)= outputs signals.

These outputs are used as entry for the 3rd box3 that is used to calculate the 2's complement (or I also think of a comparator for this).
All the output from the 2's complement are entry for the 7-segment decoder.
My doubt also the question says two 7 segments ...?

17. ### WBahn Moderator

Mar 31, 2012
18,089
4,917
What's your doubt? How many 7-segment displays are required to display the value -6 ?

It tells you specifically -- one display for the minus sign (which displays nothing when the value is positive) and one display for the for the numerical digit.

How many bits does the output of box3 produce in order to give you the difference as a two's complement value?

Given that value, how can you determine if the lefthand 7-segment display should be showing the minus sign or not?

18. ### garcon Thread Starter Member

Jan 3, 2014
33
0
To display -6, I need two 7 segment display (the first segment for "-" & second for 6).
box3 outputs 8 bits (1 bit that goes to the first 7 segment and the remaining 7 bits to the second 7 segments).

Todetermine the leftside (first 7 segment) to show minus sign or not, I can only ON g (g=1)from the 7 segments.
I am on the right truck?

19. ### WBahn Moderator

Mar 31, 2012
18,089
4,917
Maybe, but I don't think so. Since you steadfastly will not provide a sketch, it is very hard to tell if we are on the same page.

I am envisioning box three to be a box that outputs the difference between the temperatures as a two's complement integer. It neither knows nor cares about how this is going to eventually be displays. It is box4 that takes this two's complement integer and turns it into the eight signals you describe that go to the two 7-segment displays.

I am trying to focus on the signals that come out of box3 and go into box4.

20. ### garcon Thread Starter Member

Jan 3, 2014
33
0
I will try to draw and post a diagram.
4 boxes (box1, box2, box3, box4).
box1=tem generate
box2=measure actual temp.
box3= 2's comp. this receives inputs from box1 & box2. And box3 has output to the BCD and this BCD box generate the 8 signales to the two 7 segments.
I think of the BCD as it generates signals to the 7 segments decoder.
By the way, is it better to use decoder or Multiplexer in this problem?