Circuit works in lab but not in Multisim.

praondevou

Joined Jul 9, 2011
2,942
What does it do in the simulator?

Can you post the multisim file as well so the people working with it don't have to redraw the circuit?
 

praondevou

Joined Jul 9, 2011
2,942
Several things are strange. First I connected an oscilloscope to the three outputs , the two last ones are at about 1V as if the 7473 couldn't drive whatever is connected to it's outputs.

So I connected something acting as a buffer, the first I found in between. (just a 74f08 with the two inputs tied together)

Output voltages are at 5V but still nothing on the display.

Then I replaced the VCC for a DC-power supply and used for the grounds a digital ground symbol...

Now the display alternates between "0" and "L". :D

Still working on it.
 

praondevou

Joined Jul 9, 2011
2,942
Ok, the real problem is something else. IMO there is something wrong with the model of the 7473. It is a negative edge triggered FF.
In Multisim it triggers on the positive edge...

I replaced it with a 7476 which should be a positive triggered FF. It triggers on the negative edge. The simulation runs with the 7476. ;)

Not sure what's happening here.
 

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DerStrom8

Joined Feb 20, 2011
2,390
Sometimes you need to adjust the operating current for the LED (usually decrease it). Not sure if that's the case in Multisim or not. I know you sometimes have to change it in ISIS.

Der Strom
 

Thread Starter

phalanx08

Joined Nov 9, 2011
4
Ok, the real problem is something else. IMO there is something wrong with the model of the 7473. It is a negative edge triggered FF.
In Multisim it triggers on the positive edge...

I replaced it with a 7476 which should be a positive triggered FF. It triggers on the negative edge. The simulation runs with the 7476. ;)

Not sure what's happening here.
I appreciate the help. I'll rebuild it using your modifications (I can't view ms11 files using v.10), and confirm.


Sometimes you need to adjust the operating current for the LED (usually decrease it). Not sure if that's the case in Multisim or not. I know you sometimes have to change it in ISIS.

Der Strom
On your recommendation, I lowered the on current and the LED did flicker (showed only seven and the letter F). No matter how low I dropped the current (1e-20 pA haha), it still only flickered between 7 and F. If I could find the correct on current then I'd be in business.
 

Thread Starter

phalanx08

Joined Nov 9, 2011
4
Well, this is weird. My 7476 are also negative triggered.



EDIT: Even though the 7476N is also negatively triggered, it worked! Many thanks praondevou!
 
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