555 bistable

[Ghubro]

I have also fallen prey to the same problem.

Problem: Output always remains high once the trigger pulse is applied. momentarily goes to low when reset is applied and again goes to high. It should retain the low state until the trigger is applied once again.

I have been tring to simulate the bistable mode of the 555 in multisim for two days now, and I have the same problem.. I tried setting initial conditiond to zero, but that did'nt help either. The result was that instead of the output remaining always high, it now goes high once the trigger is applied and the previous problem follows. I have even trued editing the SPICE model but couldn't solve the problem. Can anyone please suggest a solution? Also please let me know if there is anything wrong with my bistable circuit.

Multisim version 11.0

OS: Windows 7 ultimate

[T.002]

I thought I have fixed it, but now checking back, I still have the problem.

Anyway, yours circuit looks fine to me.

This is how it should be:

555 bistable (java applet)
Scope 1: Reset
Scope 2: Trigger
Scope 3: Output

Breadboarding the same circuit, it also work like it should.

I suspect it's a model problem.

[Ghubro]

Thanks a lot for replying. Youu are right - the java applet you posted is exactly how the circuit should behave. I too think its a model problem. I was finally able to accomplish the objective with the help of a D flip flop set reset IC.

[bartgrefte]

Think I ran into the same problem.

Tried to build the 555 based latch circuit from http://www.buildcircuit.com/4-in-1-diy-kit-schematic/ in Multisim v11... the LED on the output is always on. But before I got there, I had to use the Convergence Assistant to get the simulation going, appearantly this had to be done: "-Shunt resistance from analog nodes to ground (RSHUNT) was changed to 100000000" , same with Multisim v12.

Setting initial conditions to zero does not make any difference in v11, same with v12.

The weird thing is, I also tried transistor-based latching circuits, but also couldn't get those to work. Although I haven't tried setting conditions to zero with those circuits, those gave a different error: "Time Step Too Small".

I build the 555 circuit I mentioned on a breadboard, and it works fine. So something is going wrong in Multisim, but what?

[ThiCop]

Hello Bart,

Can you share your .ms12 file?

I'm quite curious to have a look at what's going wrong.

[bartgrefte]

Well, I had v12 installed in a virtual computer for testing, while continuing to use v11 on the host, so I can share the files from both, they should be attached to this message.

Both files contain the 555 latch circuit from http://www.buildcircuit.com/4-in-1-diy-kit-schematic/ (that works on a breadboard) as well as a transistor based circuit that I ran into Googling., haven't tested the transistor circuit on a breadboard because I don't have all the right components for that right now (did some Ebay shopping yesterday, expecting the components in a week or two).

Did notice something: That transistor circuit no longer gives a "timestep too small" error, maybe because I set initial conditions to zero hoping that would fix the 555 circuit. Unfortunately the output of the transistor circuit is still always the same in Multisim, the LED stays on, same as the 555 circuit.

edit: I just replaced the ms12 attachment, noticed a little mistake I made (wrong value capacitor in the transistor-circuit), made no difference though.

[ThiCop]

Hello Bart,

Please always check that the pin-out of your IC (1,2,...,8) matches the descriptive pin-out information (CON, THR, TRI, ...) you're wiring.

You connected your "CON"/CV input while it should not be wired in latch-mode.

This caused some things to be connected, that should not be connected.

It should be fixed in the file in attachment.

Wikipedia gave me some extra pin-out info:

http://nl.wikipedia.org/wiki/NE555

[ThiCop]

Now the attachment.

[bartgrefte]

"You connected your "CON"/CV input while it should not be wired in latch-mode. This caused some things to be connected, that should not be connected."

Then explain why it works on a breadboard, connected the same way as in Multisim and as mentioned on that website?   Here's the breadboard version http://www.buildcircuit.com/toggle-switch-using-555/ of that same circuit with a video to show it works: http://www.youtube.com/watch?v=_C_wfb3fOcM , I could also record it myself but since that video already shows it works...

There is something strange going on though. I know which pin of the 555 has which number, but the pin-descriptions in Multisim do not match what I found with Google.

Google says http://circuits.datasheetdir.com/214/STMICROELECTRONICS-NE555-pinout.jpg

Multisim seems to have the descriptions of pins 2 and 7 switched and pins 5 and 6 seem to be switched as well.

Which means that CON, pin 5 according to Google, is indeed disconnected but according to Multisim, CON is pin 6 which is connected, but pin 6 should be threshold which is pin 5 in Multisim.

And I don't see an attachment with your messages.

edit: The 555 pinout issue seems to be around for a while, http://forums.ni.com/t5/Circuit-Design-Suite-Multisim/Multisim-10-555-differences/td-p/493547

"There are (3) 555 in my Multisim library (Ver 9). They are named 555_Timer (a 3-D Symbol), 555_Timer_Rated, and 555_Virtual. All of these have different Pin-Out vs Pin Functions. None of them agree with the Data Sheet posted at the Fairchild web site (www.fairchildsemi.com)."

[bartgrefte]

Since the edit-function has been disabled , the wiki page you mentioned shows the right pinlayout, which also does not match with the 555 in Multisim