Doing a 4-bit SR flipflop counter with a sequence of 13-11-3-5-9-1-14-7-2-6 using a 7447 and seven segment display.

Thread Starter

RDrei9

Joined Feb 20, 2024
9
My problem is that I can't implement a double digit seven segment display. I tried searching into it and can't really understand it.

My work so far... I only made 1 segment display and can't comprehend how to add one more.
1708550586974.png
 

WBahn

Joined Mar 31, 2012
30,065
You will need to decode your 4-bit binary-encoded output into two 4-bit BCD-encoded outputs. With just one nibble (4-bits) to worry about, it's not as hard as it might look at first.

Be careful about using multi-input gates and just letting unused pins float. A simulator might be okay with it, but real circuits, particularly CMOS circuits, are not. Even when using something, like TTL, where floating inputs have reasonably well-defined values, they may not be the same values that your simulator happens to use.
 

dl324

Joined Mar 30, 2015
16,931
You don't need 3 posts for the same problem.

You need a binary to BCD converter. Are you required to do it with logic? Or can you use a look up table in a programmable device?

When I designed your counter, I just used a hexadecimal display.
 

Thread Starter

RDrei9

Joined Feb 20, 2024
9
You don't need 3 posts for the same problem.

You need a binary to BCD converter. Are you required to do it with logic? Or can you use a look up table in a programmable device?

When I designed your counter, I just used a hexadecimal display.
Sorry, im quite desperate about this coursework since we are only given 1 and 1/2 day to work on it. Won;t do it next time.
 

Thread Starter

RDrei9

Joined Feb 20, 2024
9
You don't need 3 posts for the same problem.

You need a binary to BCD converter. Are you required to do it with logic? Or can you use a look up table in a programmable device?

When I designed your counter, I just used a hexadecimal display.
You will need to decode your 4-bit binary-encoded output into two 4-bit BCD-encoded outputs. With just one nibble (4-bits) to worry about, it's not as hard as it might look at first.

Be careful about using multi-input gates and just letting unused pins float. A simulator might be okay with it, but real circuits, particularly CMOS circuits, are not. Even when using something, like TTL, where floating inputs have reasonably well-defined values, they may not be the same values that your simulator happens to use.
You will need to decode your 4-bit binary-encoded output into two 4-bit BCD-encoded outputs. With just one nibble (4-bits) to worry about, it's not as hard as it might look at first.

Be careful about using multi-input gates and just letting unused pins float. A simulator might be okay with it, but real circuits, particularly CMOS circuits, are not. Even when using something, like TTL, where floating inputs have reasonably well-defined values, they may not be the same values that your simulator happens to use.
Im only gonna use simulators for this one. Can
You don't need 3 posts for the same problem.

You need a binary to BCD converter. Are you required to do it with logic? Or can you use a look up table in a programmable device?

When I designed your counter, I just used a hexadecimal display.
Im gonna do it with logic it was required for us to do it that way.
 

Thread Starter

RDrei9

Joined Feb 20, 2024
9
You will need to decode your 4-bit binary-encoded output into two 4-bit BCD-encoded outputs. With just one nibble (4-bits) to worry about, it's not as hard as it might look at first.

Be careful about using multi-input gates and just letting unused pins float. A simulator might be okay with it, but real circuits, particularly CMOS circuits, are not. Even when using something, like TTL, where floating inputs have reasonably well-defined values, they may not be the same values that your simulator happens to use.
That's what i was thinking, using two 4-bit BCD-encoded outputs, but I don't understand how to do a 0001-0000 in a double digit seven segment display without both of them outputting the same number.
 

MrChips

Joined Oct 2, 2009
30,819
You have two BCD digits. Hence you have two 4-bit inputs:
D2 C2 B2 A2 and D1 C1 B1 A1.
Treat them as eight independent inputs.

Draw the Karnaugh for each of the eight flip-flops.
 

dl324

Joined Mar 30, 2015
16,931
You have two BCD digits. Hence you have two 4-bit inputs:
D2 C2 B2 A2 and D1 C1 B1 A1.
Treat them as eight independent inputs.

Draw the Karnaugh for each of the eight flip-flops.
The OP has implemented the circuit as a 4 bit counter and wants to decode to 2 BCD digits.
 

MrAl

Joined Jun 17, 2014
11,487
That's what i was thinking, using two 4-bit BCD-encoded outputs, but I don't understand how to do a 0001-0000 in a double digit seven segment display without both of them outputting the same number.
Either you use two 7 segment drivers or you use one and do multiplexing. Multiplexing would be more complicated, probably too much so for this assignment.
 

dl324

Joined Mar 30, 2015
16,931
Sorry, im quite desperate about this coursework since we are only given 1 and 1/2 day to work on it. Won;t do it next time.
You're in luck because implementing the decoder won't take very long. It's just a 4 variable Kmap with 8 outputs.

It took 10 more gates. Less if I took the time to see which gates from the counter logic could be reused.
 

dl324

Joined Mar 30, 2015
16,931
I passed my cw which compost 40% of my grds and got a perfect score.
Glad you were able to complete the assignment on time; and perfectly no less.

If you're going to continue in this field, you should work on learning how to draw more readable schematics:
1708615873317.png
Style matters in schematics. Mine is a combination of what I decided was good in datasheets from Texas Instruments, RCA/Harris, and Motorola.

The middle display uses a general purpose 4 bit binary to BCD converter using the Double Dabble algorithm that's a common problem for school. Many have posted their problem, but few have completed it (or at least, they never posted their work). That implementation takes 6-8 more gates than the specialized one for your problem.

The simulator I use (Digital Works) makes it easy to troubleshoot logic problems without having to probe each of the nets. You can see from the inputs to the flip flops that the next count will be 7.
 
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