555 bistable

[T.002]

Hello.

I'm trying to build the 555 bistable circuit, but the simulation doesn't work well for me.  

Problem: the output is always high.

When reset is held low output is low (good), but when it flip back to high, output turn to high immediately.

(I have build the same circuit on the breadboard and it works.)

Is there a way to fix it?

Thank you.

[digitalguy]

It's hard to see how this circuit works on a breadboard since you have left out some very basic connections for a bistable circuit (I'm assuming that is what you're after). I made some very basic changes, but added the necessary connections and the components needed for a bistable. The values of the components can be changed to meet your needs.

Howard

[T.002]

What you did is the astable circuit, the bistable circuit work like a flip-flop.

http://en.wikipedia.org/wiki/555_timer_IC#Bistable_Mode

[ThiCop]

Hello,

The implementation of  the bistable circuit is correct.

I am also not able to reproduce your problem, because I get the behavior I expect from a flip-flop.

How do you simulate your circuit?

You should go to Simulate > Run.

If you click on the A button (of your keyboard), then you should see your LED switch from the on-state to off-state (or from off to on depending on the starting state of your switches).

The burning LED has orange arrows (like in the image) the non-burning LED has non-coloured arrows.

Does this work at your side?

[T.002]

Hello,

I forget to change the keyboard shortcut of the switches, they should not be the same.

How to reproduce:

Initial: The switches are open.

If you click on the reset switch to close and click again to open it, you should see the led burn.

That should not be the case because set/trigger is not active (not low, switch open).

[ThiCop]

Hello,

I've probably changed it automatically (to two different switches) without thinking about it. 🙂

So everything is ok now?

[T.002]

What I mean to say with the previous post is that the problem still exist and how one can reproduce the error that I have.

With my current situation, the output is high when both switches are open. Output should be low right?

[ThiCop]

Hello,

There does indeed seem to be a problem with the 555 component you're using.

Which component database are you using?

Which version of Multisim are you using?

[T.002]

Hello,

It's indeed because of the 555 component that I'm using.

I have attached the component report below.

(I'm using Multisim version 11.0)

I have edited the SPICE model of the component using the model posted by Maxish here: http://forums.ni.com/t5/Circuit-Design-Suite-Multisim/555-Wizard-Bad-v10-Multisim/m-p/498157

It seems to work well now.

Thank you for yours help.

[T.002]

Hello,

Without changing the component model and changing the interactive simulation settings also solve the problem.

Initial conditions: Set to zero.