7 Segment LED (Digital Works) Only getting 4 numbers.

Thread Starter

Madangopal jha

Joined May 24, 2011
9
Hi guys, I've an assignment to print out the current year (21) follow by my 6 digit student ID using a 7-Segment LED display, where I'm only allowed to use 3 sequence bit generators. (21979502). Build a circuit using only AND, OR, NOT, NAND and NOR logic gates to simulate the counter.

I've been toiling over this problem the last 2 days (about 20 hours in total), checking my truth tables again and again, checking my Boolean Equations, and checking the simplification again and again. I've built the circuit (more than once), but I don't understand why I'm only getting 4 digits? (2,1,9 and 0). I've been trying very hard to get this done on my own, whilst learning a lot about it, but I'm completely stumped by this so I feel it's finally time to ask for help.

I've provided: My Truth Table, My Boolean Equations (and Simplifications) as well as my attempted Circuit.

I'm not asking for the answer, I just need a little guidance on where I've gone wrong, as I'm unsure the problem now after checking and double checking my work.
 

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dl324

Joined Mar 30, 2015
13,505
I've provided: My Truth Table, My Boolean Equations (and Simplifications) as well as my attempted Circuit.
Have you verified that the sequencers are counting correctly?
I'm not asking for the answer, I just need a little guidance on where I've gone wrong,
That's the right attitude to have. Kudos to you.

I assume the colors are to make it easier for you to follow the logic, but schematics are usually monochromatic. Using a different style would make it easier for you to keep track of things. You labeled the segment drivers, but you could also have labeled the logic for each AND gate.
 

absf

Joined Dec 29, 2010
1,963
I tried simulate your simplified boolean equation on proteus and I am not getting the result of "21979502". Instead I got "29X015Y2".

X is like a "9" without segment c while Y is like a 7 without segment c.

So there must be some mistakes with your simplification of your truth table. Try it again and I wish you;ll be successful if you put some more effort.

Attached is my simulation.7SEG_DISPLAP.PNG
 

Thread Starter

Madangopal jha

Joined May 24, 2011
9
Have you verified that the sequencers are counting correctly?
That's the right attitude to have. Kudos to you.
I wasn't even aware I had to, or even knew I could do that, or how I'd go about doing it. I've been using the software for a couple days, but wasn't aware you could verify the sequences in counting order. This is an extremely helpful point and should make it easier to figure out where I've gone wrong. But from what I can see, I've been getting "2, 1, 0, 9" in that order, so it's safe to assume what numbers are there, aren't in the correct order. I'll attempt to figure out how I can go about verifying how I can go about getting the numbers to display in the correct order (first).

I assume the colors are to make it easier for you to follow the logic, but schematics are usually monochromatic. Using a different style would make it easier for you to keep track of things. You labeled the segment drivers, but you could also have labeled the logic for each AND gate.
Yes, the colors are there (for the moment) so it's easier for me to follow whilst I try to get it working fully. In future, I plan to label each gate separately (to make it even easier to follow) as I plan to create an extended truth table for every gate in the circuit. :)
 

Thread Starter

Madangopal jha

Joined May 24, 2011
9
I tried simulate your simplified boolean equation on proteus and I am not getting the result of "21979502". Instead I got "29X015Y2".

X is like a "9" without segment c while Y is like a 7 without segment c.

So there must be some mistakes with your simplification of your truth table. Try it again and I wish you;ll be successful if you put some more effort.

Attached is my simulation.View attachment 250724
Thank you. If you look at my truth table, I notice an issue with Segment D, I think it's simplified a little too much? (If that makes sense), since there's no B present, so this only gives 4 outputs. (Not 8). You given me some insight on where I've hiccuped, with the numbers not displaying in the correct order and also that there could be further issue with my truth table simplifications. I'll continue to work on these and get back to you. :) But, it is possible for the Segment to display more than 4 numbers in Digitalworks? I'm just wondering if how I'd verify it works correctly if I can only see the 4 numbers unless the reasoning *is* the simplification and the order of numbers?
 

absf

Joined Dec 29, 2010
1,963
But, it is possible for the Segment to display more than 4 numbers in Digitalworks? I'm just wondering if how I'd verify it works correctly if I can only see the 4 numbers unless the reasoning *is* the simplification and the order of numbers?
You can display all 8 digits sequentially one after another by putting 3 switches on the input A,B, and C.

For me, I used a binary counter 7493 clocked with one Hz from proteus. Since you only have 8 digits, I skipped the first flip flop and start the counting from Clock Input B; or else it would count to 16 naturally if all FF are used; the 3 outputs Q1,Q2,Q3 become the inputs of A,B,C. Using a LED, I connected an extra 3-inputs OR gate to indicate that it is the first digit of your number.
 

dl324

Joined Mar 30, 2015
13,505
wasn't aware you could verify the sequences in counting order.
Didn't you enter the sequences? You can right click on a sequencer and select "Edit Sequence" to view or edit the sequence.

Are you allowed to use Karnaugh maps?
But, it is possible for the Segment to display more than 4 numbers in Digitalworks? I'm just wondering if how I'd verify it works correctly if I can only see the 4 numbers unless the reasoning *is* the simplification and the order of numbers?
Yes, it's possible. I entered your circuit in Digital Works (your problem, my design) and have it working.

I used switches instead of sequencers to check the logic.
 
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