Control two 7-segment displays

[Fatima Hasan]

Homework Statement

Homework Equations

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The Attempt at a Solution

I tried to design the circuit to control the first 7-segment , but I didn't get the correct answer.

Could someone check where is my mistake ?

 

[berkeman]

I'll check it over in more detail in a bit, but there are only 4 binary inputs to this 2-digit display, right? What is the maximum decimal number that can be displayed? When the lead digit is zero, do you want to display a "0" or just leave that display off?

 

[Fatima Hasan]

What is the maximum decimal number that can be displayed

9 ?

 

[berkeman]

No. I mean what is the decimal equivilant of 0b1111 = 0xF = 0d?

 

[Fatima Hasan]

When the lead digit is zero, do you want to display a "0" or just leave that display off?

Want to display a "0" .

 

[berkeman]

Want to display a "0" .

Okay. You see how "off" would be easier, right?

So start with a table like this:

ABCD  d1 d2
0000  0  0
0001  0  1
etc.
1111   ?  ?

and then check your work against that table...

 

[berkeman]

Oh wait, maybe you already did that. I was confused by all of the "1" entries for the 2nd display, but maybe it's just because you are displaying "0" so much. Let me take a closer look...

 

[berkeman]

Shouldn't b2 and c2 always be on?

 

[Fatima Hasan]

Shouldn't b2 and c2 always be on?

b1 and c1 are always on.
For example , when the decimal number is 12 ( d1=1 and d2 = 2 ) :
b1 and c1 = 1 .
a2=0 , b2 =0, c2 = 0 , d2 = 1 , e2= 1 , f2= 0 and g2 = 1.

 

[berkeman]

Ah, got it. Sorry, I had the numbers of the two displays mixed up. So which digit is this simulation for?

 

[berkeman]

Also, are you using a common-cathode or common-anode display? It looks like the segments are just inverted in your diagram, if it's for the most significant digit. Switch to a common-cathode display if you want to drive the segments with "1 = ON"...

 

[Fatima Hasan]

So which digit is this simulation for?

The first one (d1).

 

[Fatima Hasan]

Also, are you using a common-cathode or common-anode display?

I don't know what is the difference between them , we haven't covered that yet.

 

[berkeman]

I don't know what is the difference between them , we haven't covered that yet.

You would drive the segments of a common-cathode LED display high to turn them on. The common-cathode of all of the LED segments is connected to ground:

https://www.electronics-tutorials.ws/articles/segment1.gif

https://www.electronics-tutorials.ws/articles/segment1.gif

In a common-anode LED display, you connect the common-anode to your +5V supply, and drive the segments low to turn them on. Your display in the simulation appears to be the common-anode type, since the segments are off when you drive them high, and on when you drive them low. That may be your only issue with this problem...

 

[Fatima Hasan]

Your display in the simulation appears to be the common-anode type, since the segments are off when you drive them high, and on when you drive them low.

Got it , thanks a lot for your help.

 

[berkeman]

Got it , thanks a lot for your help.

Great! I think I would turn off the dot though...

 

[Fatima Hasan]

Great! I think I would turn off the dot though...

This is the simulation for the second digit :
https://www.physicsforums.com/attachments/234945

But I didn't get the correct answer , It should be 0 instead of 1 . Also , I am not sure if that is the minimum number of gates or not.
Could you check it please ?

 

[Fatima Hasan]

Great! I think I would turn off the dot though...

I solved the question again and got different answers .
In my first solution, I started by doing simplification then I took the commons between them and I got 28 gates in the final answer ... While in my second solution , I did the opposite by taking the commons in the beginning and then I got 24 gates in my final answer ...

Here's my first solution :

The second one :

Which method is the correct one ?
Thanks .

 

[Mark44]

I mean what is the decimal equivilant of 0b1111 = 0xF = 0d?

@berkeman, did you intend something else for that last number?

 

[berkeman]

@berkeman, did you intend something else for that last number?

I was just asking what the "?" would be. 0xF = what in decimal... The OP seems to be doing okay now, I was a bit confused early on in the thread about which digit was which.

 

[berkeman]

Which method is the correct one ?

Do they both simulate correctly? If so, the one with the fewer gates would be the preferred answer, no?

Also, have you looked at IC schematics for the parts that do this function? That may be a good cross-check for your work. Just Google 7-segment display drive ICs or similar, and use Google Images to start looking at their schematics.

 

[Fatima Hasan]

Do they both simulate correctly? If so, the one with the fewer gates would be the preferred answer, no?

Also, have you looked at IC schematics for the parts that do this function? That may be a good cross-check for your work. Just Google 7-segment display drive ICs or similar, and use Google Images to start looking at their schematics.

Thanks for your help .

 

[Mark44]

I was just asking what the "?" would be. 0xF = what in decimal... The OP seems to be doing okay now, I was a bit confused early on in the thread about which digit was which.

I thought that might be what you were doing, but "0d?" was confusing to me, since 0xd would be 13 (decimal), which is different from 0xF.

 

[berkeman]

Yeah, sorry. Maybe 0d is not a standard prefix notation. I've definitely seen it used as a decimal prefix in the past in some contexts, though.

https://forums.ni.com/t5/LabVIEW-Id...x-0d-0b-0o-in-numeric-constants/idi-p/3070288