NI Home > Community > NI Discussion Forums
Reply
Member
Arnie_8446
Posts: 10
0 Kudos

Working with Subcircuits in Multisim 10 Student Edition

Hello Everyone,

I built this circuit mainly using subcircuits.  It's supposed to display a 4-digit hexadecimal number using a single BCD to 7- segment decoder to operate 4 displays. I am using 16 switches organized as four groups of 4 switches. Each switch outputs a 1 or 0.  I constructed a 2 bit-counter, 16-4 multiplexer, a 7-segment decoder, and a 7-28 demultiplexer connected to 4 seven-segment LED display.  When I test my subcircuits separately, it works fine.  But all together in the circuit it does not work.  I plugged in an oscilloscope to the 2-bit counter, and I don't get any pulses, but it works in the subcircuit.  Is there some kind of special trick on how to make this work?  I've attached my files. Maybe someone else has run into this problem before.

Thanks!
Active Participant
lacy
Posts: 1,233
0 Kudos

Re: Working with Subcircuits in Multisim 10 Student Edition

I tested the counter and I am getting a signal at both outputs with no changes made to the circuit. I know the circuit is not operating as you want it to, but right now I can't isolate what is causing the problem.

In such a situation, I usually Isolate one subcircuit at a time, get it working correctly and then hook it to the second one and so forth. You may have to do this in order to find out where it deviates from what you expect as an output.

This is the only thing I can suggest at the moment. I will continue looking into this, but with so many nested subcircuits it may take a while. I cannot guarantee finding a solution, but I will try.

Kittmaster's Component Database
http://ni.kittmaster.com

Have a Nice Day
Active Participant
lacy
Posts: 1,233
0 Kudos

Re: Working with Subcircuits in Multisim 10 Student Edition

[ Edited ]

I am not certain if this was intentional, but when I run the simulation I get the numbers changing, but also the displays get switched. Instead of displaying a 4 digit number at the same time I get one display showing one number and then it will switch to another display.

I am thinking it has to do with the last multiplexer. By switching the outputs from one display to another it takes away the voltage to the first display and therefore switches it off.

 



Message Edited by lacy on 03-30-2008 10:22 AM
Kittmaster's Component Database
http://ni.kittmaster.com

Have a Nice Day
Active Participant
lacy
Posts: 1,233
0 Kudos

Re: Working with Subcircuits in Multisim 10 Student Edition

Here are my conclusions. Your circuit on my machine is working. The thing that is not working correctly (my opinion) is the fact that when you do the switching in the last multiplexer it blanks one display and then lights the next one. If you are wanting all the diplays to be active at the same time you are going to have to get into the last multiplexer and find a way to do that.

My previous post is accurate. It cylces the displays instead of having them all on at the same time. I am not sure this was intended, but if it was then your circuit is working fine.

I hope I have helped some.

Kittmaster's Component Database
http://ni.kittmaster.com

Have a Nice Day
Active Participant
lacy
Posts: 1,233
0 Kudos

Re: Working with Subcircuits in Multisim 10 Student Edition

If everything is working as I suspect, then I have to say that this is a brilliant circuit and design.

I would like to bring to your attention about the X2 Subcircuit has your test setup still inside it. Before you finalize this you might consider deleteing these testing components. Also the 7 segment display inside this subcircuit is the wrong type. It should be a common cathode. I would also suggest putting a 50 ohm resistor in line with it to ground like the other displays in order to eliminate an error message popping up.

Great circuit.

Kittmaster's Component Database
http://ni.kittmaster.com

Have a Nice Day
Member
Arnie_8446
Posts: 10
0 Kudos

Re: Working with Subcircuits in Multisim 10 Student Edition

Hi Lacy,

I hope you're doing well.  You're right! The problem was with my PC and Multisim.  I installed Multisim in my other PC and the circuit worked fine.  On a side note, it is the intend to display one hexadecimal number at time in the 7-segment LED's and it is also supposed to strobe each 7-seven LED's display every 30 seconds.  And yes, I knew about the wrong display in the subcircuit.  It was very late at night and I did not pay attention on which one I picked up.  At any rate, thanks for the comments!

Take Care!
Arnie
Active Participant
lacy
Posts: 1,233
0 Kudos

Re: Working with Subcircuits in Multisim 10 Student Edition

I am glad you got it working. I thought as much about the cycling displays after analyzing it more carefully. According to what I see now though it is cycling way faster than every thirty seconds. You may have it this way for testing purposes (which is what I would do instead of waiting forever for the simulator time to reach 30 sec.). Reguardless, I am happy you are happy with it.

Congratulations on a wonderful design.

Kittmaster's Component Database
http://ni.kittmaster.com

Have a Nice Day