connect 74LS47 to seven-segment display does not work?

[lacy]

I re-examined the circuit and it does work at 5V. I apooglize for my error on this, but I am not perfect all the time (Laughing). The problem stemmed mostly from the digital Hex displays and the digital probes. These have caused problems before in other circuits. I replace them with the non-digital displays and probes and that seem to cure it up, but I never changed the voltage back to see if that was a part of the problem.

You can use them in the simulator at 12V with no errors. This is something that may need to be examine at NI. If I can apply any voltage to an IC without an error popping up then like Lodin said that is problematic at the very least.

I thank you for bringing this to my attention. Usually when I screw up I do a good job of it.

Message Edited by lacy on 03-16-2008 08:24 AM

[jonnyBGood]

The Dgnd was the problem! thanks! It now works.

However, the digital displays do not alternate the way they are supposd to. But this might be because the simulated transisters can't turn on and off fast enough.

What you should see on the displays is only a 5 and a 6. and they are not to show up on both displays! but they are.

[lacy]

I think you are correct. I saw the same thing. It may be the rise and fall time of the displays or it could be the lag time of the simulator causing this. The voltages in some cases just don't instantaneous switch. It takes time for the transition from high to low or vice versa This is what I would call the lag time. It probably would not do this in a real circuit. So I would say your circuit would work just fine..

[Q Gene]

I know your post is from some time ago but here goes anyway.  I'm using Multisim 11 and every time I try to place a VCC on the schematic the software tells me that I have hidden power pins using on-page connectors with the name "VCC".  I can't see any on-page connectors.  The VCC and ground pins on the IC's are generally hidden and are powered just fine by the hidden VCC.  But I need to add another voltage source to power the logic.  I feel like I'm missing something very fundamental in the process.  I also have trouble when I move the circuit to the breadboard and I get all sorts of connectevity errors that are all about the, now visible, VCC and ground pins.  Again...am I missing something very fundamental here?

Q Gene

[Fernando_D]

Hi,

Many digital components have the power/ground pins hidden to reduce the number of wires on the schematic and these pins are pre-configured to have the power and ground pins virtually connected to the schematic's global power and ground nets.

In Multisim 11 we introduced On-Page Connectors to symbolize virtual connections and, in this particular case, when you try to place VCC, Multisim lets you know that a digital component has a hidden power pin with the same name (VCC), and this pin will be virtually connected to the power source

with a hidden on-page connector.

If you do not want to connect the power source to the power pin, you can change the net name.

I hope this helps.

Regards,

[01031990]

Hi All

I have a problem in working the 7 Segment i already connected to the 7447 but the output to the 7 segment voltage and current is so small

if anyone can help ?

[Tom__Sedlack]

A few things:

1)  The 7447 has active low outputs so you would want to use a common anode display with the CA pin tied to 5V.

2)  Multisim wants all pins to be terminated.  Even though the spec sheet for the 7447 says you can leave the BI pin open, it needs to be pulled high otherwise Multisim assumes they are at 0V.  The same goes for the other inputs.  Always pull open pins to the desired logic level in MS!

3)  The voltage probe tool can be your friend.  If you probed your VCC terminal (in the upper left corner of your schematic), you would have seen it had 0 volts on it.  Another quirk of MS.  The logic circuits worked but if you tied the CA pin of your display to VCC, it would not get voltage.

4)  You would also need to put a digital ground on your schematic to make the logic happy.

Attached is the modified section of your schematic.

---

[01031990]

TOM THANKS MAN U REALLY HELPED ME A LOT

specially tomorow i will submit the final report for the project :):)

[jamsar13]

I cannot for the life of me get my seven segment to work....HELP PLEASE!!!! 😞 *sigh*. It works when i connect it manually on breadboard, but not in multisim

[Tom Sedlack]

Jamsar13,

Please read my other post 2 above yours. I made the changes listed  (1,2, and 4) to your circuit and it worked correctly.

Tom