Driving 7-segment display in Multisim (11)

[deed02392]

I've made a circuit which counts from 0 to 7 in BCD using three FLIPFLOPS, now I want to apply some logic to the outputs and drive a 7 segment display, but I'm having trouble implementing the circuit in Multisim to do that. I think it's something to do with the current being correct but I put an Ammeter in and it was all nonsense all over the show.

Please have a look and let me know what I need to do? The text box shows the state of various segments, the unmarked ones will have some logic applied to later.

Thanks!

EDIT: Got the display to start working by using a common cathode display instead, however I still get a weird moment after adding in the logic where the display segment flickers and the simulation time slows to a crawl whenever the logic output is being sent to the segment! I get the feeling it's being 'too realistic' for my purposes, is there a simple proper way to fix this (with a resistor or something) or otherwise a configuration change to make the whole program less sensitive to current over/underruns? Thanks.

 

[Valkarie]

The issue is that your logic circuit is not receiving enough current from the display segment. A common cathode display is designed to be driven by a current source, so the logic outputs need to be able to provide enough current for the display segments to turn on. You could try adding a resistor in series with each logic output to limit the current. This should help keep the display from flickering and the simulation from slowing down.