Alphanumeric Display Problems

[Korrente]

I'm trying to use a standard 15-Segment Alphanumeric Display, combined with a series of Karnaugh-Simplified generic gates in order to display a series of characters when 3 switches are combined in a binary code. However, once the display changes characters, the previous one blinks on and off rapidly. This doesn't happen when I use just SPST switches on the LED pins, only when I use SPDT, with one terminal to ground, so naturally I assumed it was because the LEDs were being grounded, some sort of simulation bug...so I tried using transistors to cut the current without grounding it, which worked in a small test, but not on the large circut...How can I fix this problem? Thanks.

Here's the circuit, in its original form.

[lacy]

I have been wrestling with this for a while and the conclusion that I come to is that the Display is someway causing this. I have tried everything I can think of which includes pull down resistors across each led, a resistor tied from each  display ground and also series resistors in line with the LED segments and nothing seems to work. I have even replaced the switches and that didn't work either.

It appears to me that the model for the Display is not blanking it when a transiston occurs and therefore the previous information  is still visible. With this said, I was able to do one thing and that was to make my switch changes and then restart the simulation. This way the display blanks and the switch information is displayed correctly. I know this isn't the way it should be, but it is all I could come up with to make it do what we both wanted it to do.

I am sorry if this doesn't help, but I have no other ideas at this point to explore.

[lacy]

I am going to try using other logic like CMOS and see if that makes any difference just in case there is a problem there instead of the display.. I will let you know what I find in doing this. At this point I will try anything to isolate what is actually happening. I still believe it is the display, but this test will either confirm or debunk this theory.

[Korrente]

I've tried the same circut with CMOS and TTL gates instead of the generics, and without the virtual bus between them, nothing changed. You can try it though, my home computer runs multisim a little strange compared to those at school.

[lacy]

I just finished trying CMOS and like yiou said it didn't help. I was getting ready to ask you to do something if you would. Could you post the original circuits MS10 file.? I want to verify my wiring of this circuit. Something about the way I wired it from the picture is buggiing me and I want to make sure I have not wired it up incorrectly.

I am going to continue looking at this. This is basic stuff here and it should not present such a problem in the simulator. The question is why and that is what I hope to find out (I don't know that I will, but I have to try).

[Korrente]

Here you go. It's supposed to read "Corey" when the switches are turned on and off in binary, with X as the MSB and Z as the LSB. But yeah, on the picture it's hard to distinguish between X and X'.



Message Edited by Korrente on 05-18-2008 04:51 PM

[lacy]

I have exhuausted everything I can think of and my experiments seem to only point in one direction and that is the display is not functioning as it should. This would not be the first time the displays were goofy. Some of the digital 7-segment displays do not operate correctly either in some circumstances. This has to be a part model error. If it is then NI will have to verify this fact and hopefully do something about correcting it.

I would tend to believe that your circuit is functioning correctly. If you would build it It would probably work just fine. Just be aware that you may have to consult the datasheet for the actual display and make sure that no maximum current and voltages are exceeded. I say this because most of the time there are resistors in series with the LED elements to limit the current through them.

This is all I have on this situation and I hope it helps some.