Led flashing simulation in Multisim

[TheKnight]

Hi all,

I've been following a schematic where two LED's blink. I was picking the parts carefully, making sure of right power and it doesn't work. In fact, it's working two-three times both LED's blink but that's it. An error appears saying that Multisim will try to fix that error but cannot. See the schematic below. There is one that I followed while the other one is the schematic from Multisim.

What might be the problem? It's a very simple scheme, but maybe there's an error in Multisim? Thanks.


Components values
R1 - 470 Ohm
R2 - 470 Ohm
R3 - 3.9 kOhm
R4 – 3.9 kOhm
P1 - 50 kOhm
C1 – 47 μF / 16V
C2 - 47 μF / 16V
T1 - BC 547 B
T2 - BC 547 B
D1 - LED Standard , 5 mm , red
D2 - LED Standard , 5 mm , red

 

[user_88]

I put the circuit on LTSpice ... used 2N2222 transistor ... seemed to work .... Have you included the ground node on your simulation?

 

[alec_t]

Try replacing the pot P1 with a fixed 10k resistor and see if the sim runs ok.

 

[TheKnight]

@user_88 - Tried with the 2N2222 transistor and put the ground and the LED only turns on and doesn't turn off. Stays constantly turned on.

@alec_t - Well I think that it has the same effect, but still tried it and didn't work.

You have used LTSpice and it worked. I think that it's kind of Multisim error as I've read a lot of topics that Multisim is full of bugs. So I put the source voltage to 18V and still it works so I think that it's a program bug. Don't know if I should switch the program cause It's bugging me quite much but don't know which one should I choose. Is proteus good?

 

[alec_t]

@alec_t - Well I think that it has the same effect, but still tried it and didn't work.

Well at least that rules out the pot spice model as being the cause.

 

[TheKnight]

What simulator are you using if using any?

 

[crutschow]

Many on this forum use LTspice from Linear Technology since it's free and works well.

If you post the Multisim .ms file I'll try to simulate it.

 

[TheKnight]

Well been reading a lot on this subject, but as always everyone has his own opinion. I will set out to try LTSpice though I have Proteus and haven't tried to see how it's handling.

EDIT : The attached file is now working.

 

[crutschow]

Well been reading a lot on this subject, but as always everyone has his own opinion. I will set out to try LTSpice though I have Proteus and haven't tried to see how it's handling.

EDIT: Says that .ms is an invalid file.

If you can ZIP it, it will allow that to be posted.

 

[crutschow]

Downloaded your file, but unfortunately my free copy of Multisim from Analog Devices says it cannot open a file created on a different version of Multisim. Bummer.

Can you post a schematic of the exact circuit you are simulating (screen dump of the Multisim schematic)?

 

[TheKnight]

Sure. I hope this is what you were looking for.

 

[crutschow]

I simulated you circuit in Multisim with no error and it oscillated with a period of about 592ms (see below). But I found it would not work properly unless R5 was at 90% or greater. A lower setting on R5 apparently upsets the proper feedback from the capacitors. If you want to adjust the frequency with a pot, you can use a dual pot with separate connections in series with R3 and R4. R3 and R4 should have no connections between them.

 

[TheKnight]

Does it work so that the LED's flash in periods? I changed potentiometer percentage to 90% but still as I said, only one flash then it's still.

 

[crutschow]

Does it work so that the LED's flash in periods? I changed potentiometer percentage to 90% but still as I said, only one flash then it's still.

As you can see from the oscilloscope in my simulation, the LEDs alternately light with the simulation continuing.

Don't understand why yours stops. What time frame are you using (how long do you let the simulation run)? The simulation does run very slowly.

 

[TheKnight]

Well even if it does, I leave the simulation for more than 10 seconds and the first flashing is done in less then a second, so I don't suppose that that should be the problem.

 

[crutschow]

Well, your and my circuit appear to be identical, so I'm at a loss as to why yours doesn't simulate the same as mine, unless it's just due to different versions of Multisim. Mine is a free copy of Multisim 11 from Analog Devices.

 

[TheKnight]

I don't think that it is because of the different versions, because I don't think that they do that much update of the resistors, models etc so it shouldn't have a problem opening yours version.

Anyway, mine version is the Power Pro Edition.