# 555 Timer (Astable Multivibrator) Simulation Help **URL:** \ **Category:** projects\ **Created:** [July 12, 2025, 11:24pm UTC](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741 "2025-07-12T23:24:33Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![leandroding](https://forum.fritzing.org/user_avatar/forum.fritzing.org/leandroding/32/25672_2.png) [@leandroding](https://forum.fritzing.org/u/leandroding)\ **Post date:** [July 12, 2025, 11:24pm UTC](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741/1 "2025-07-12T23:24:34Z")
Hi, I would be glad if anyone could help me confirm whether I’m wrong or not. As you can see in the image below, I have a simple circuit using the IC555. It works in TinkerCad but not in Fritzing. I tried all the available diodes, but the result was the same. Has anyone experienced a similar issue when using different simulators? [555.fzz](https://forum.fritzing.org/uploads/short-url/8FFCHhFtjifmcWRTbleRO4L4v3l.fzz) (9.5 KB) ![image](https://forum.fritzing.org/uploads/default/original/3X/8/c/8c39423c0db8b459bff97b291d4267b3d84f33eb.png) ---
**Author:** ![vanepp](https://forum.fritzing.org/user_avatar/forum.fritzing.org/vanepp/32/4426_2.png) [@vanepp](https://forum.fritzing.org/u/vanepp)\ **Post date:** [July 13, 2025, 12:21am UTC](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741/2 "2025-07-13T00:21:06Z")
For me it gives a spice error, although the diodes appear to have the same spice model as the one in the simulation bin, but that may not be the part it is unhappy with. ![capture](https://forum.fritzing.org/uploads/default/original/3X/3/1/3101135eea1a79543c58acebae9324e4b9736ab2.jpeg) The simulator gave an error when loading the netlist. Probably some SPICE field is wrong, please, check them. If the parts are from the simulation bin, report the bug in GitHub. Errors: stdout Note: No compatibility mode selected! stdout Circuit: simulator netlist stderr Warning: Model issue on line 4 : stderr .model labpowersuppymodel ilimit(r\_out\_source=1 r\_out\_sink=1 i\_limit\_sou … stderr Unknown model type ilimit - ignored stderr Error on line 7 or its substitute: stderr av1 4\_v1\_aux 4\_v1\_aux2 0 4 labpowersuppymodel stderr MIF-ERROR - unable to find definition of model labpowersuppymodel Netlist: Simulator Netlist D3 4 3 DI\_1N4001 XU1 6 1 4 5 6 7 4 0 UA555 .model labPowerSuppyModel ilimit(r\_out\_source=1 r\_out\_sink=1 i\_limit\_source=5 i\_limit\_sink=5) V1Aux 4\_V1\_aux2 4\_V1\_aux 5 V1 4\_V1\_aux 0 12 AV1 4\_V1\_aux 4\_V1\_aux2 0 4 labPowerSuppyModel C1 6 0 47n IC=0 C3 0 2 10u IC=0 - Multimeter, com probe connected to 0 and voltage probe connected to 2 D4 3 2 DI\_1N4001 C4 5 0 10p IC=0 C2 1 3 10u IC=0 R1 1 6 68k \*SRC=1N4001;DI\_1N4001;Diodes;Si; 50.0V 1.00A 3.00us Diodes, Inc. diode .MODEL DI\_1N4001 D ( IS=76.9p RS=42.0m BV=50.0 IBV=5.00u CJO=39.8p M=0.333 N=1.45 TT=4.32u ) .SUBCKT UA555 32 30 19 23 33 1 21 999 \* TR O R F TH D V GND \* \* Taken from ngspice examples: [ngspice/examples/p-to-n-examples/555-timer-2.cir at master · imr/ngspice · GitHub](https://github.com/imr/ngspice/blob/master/examples/p-to-n-examples/555-timer-2.cir) and modified to include the ground. And this model has been… \* Taken from the Fairchild data book (1982) page 9-3 \*SYM=UA555 \*DWG=C:\SPICE\555\UA555.DWG Q4 25 2 3 QP Q5 999 6 3 QP Q6 6 6 8 QP R1 9 21 4.7K R2 3 21 830 R3 8 21 4.7K Q7 2 33 5 QN Q8 2 5 17 QN Q9 6 4 17 QN Q10 6 23 4 QN Q11 12 20 10 QP R4 10 21 1K Q12 22 11 12 QP Q13 14 13 12 QP Q14 999 32 11 QP Q15 14 18 13 QP R5 14 999 100K R6 22 999 100K R7 17 999 10K Q16 1 15 999 QN Q17 15 19 31 QP R8 18 23 5K R9 18 999 5K R10 21 23 5K Q18 27 20 21 QP Q19 20 20 21 QP R11 20 31 5K D1 31 24 DA Q20 24 25 999 QN Q21 25 22 999 QN Q22 27 24 999 QN R12 25 27 4.7K R13 21 29 6.8K Q23 21 29 28 QN Q24 29 27 16 QN Q25 30 26 999 QN Q26 21 28 30 QN D2 30 29 DA R14 16 15 100 R15 16 26 220 R16 16 999 4.7K R17 28 30 3.9K Q3 2 2 9 QP .MODEL DA D (RS=40 IS=1.0E-14 CJO=1PF) .MODEL QP PNP (BF=20 BR=0.02 RC=4 RB=25 IS=1.0E-14 VA=50 NE=2 CJE=12.4P VJE=1.1 MJE=.5 CJC=4.02P VJC=.3 MJC=.3 TF=229P TR=159N) .MODEL QN NPN (IS=5.07F NF=1 BF=100 VAF=161 IKF=30M ISE=3.9P NE=2 BR=4 NR=1 VAR=16 IKR=45M RE=1.03 RB=4.12 RC=.412 XTB=1.5 CJE=12.4P VJE=1.1 MJE=.5 CJC=4.02P VJC=.3 MJC=.3 TF=229P TR=959P) .ENDS .option savecurrents .option interp .OP \*.TRAN 1ms 100ms - .AC DEC 100 100 1MEG .END Note I know almost nothing about simulation @fai (who wrote the simulation code) will probably be able to give you a better answer. Peter ---
**Author:** ![leandroding](https://forum.fritzing.org/user_avatar/forum.fritzing.org/leandroding/32/25672_2.png) [@leandroding](https://forum.fritzing.org/u/leandroding)\ **Post date:** [July 13, 2025, 5:05am UTC](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741/3 "2025-07-13T05:05:15Z")
Thanks for replying. Although I’m not using parts from the simulator bin (all the parts I used are from the core section), I’m analyzing the information you sent and will check if the same issue occurs on my end so I can report it as a bug. ---
**Author:** ![vanepp](https://forum.fritzing.org/user_avatar/forum.fritzing.org/vanepp/32/4426_2.png) [@vanepp](https://forum.fritzing.org/u/vanepp)\ **Post date:** [July 13, 2025, 11:48am UTC](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741/4 "2025-07-13T11:48:49Z")
I see that power supply isn’t in the simulator bin. That may mean that while it has a spice model (which my original did not), that it doesn’t work yet and thus isn’t yet capable of simulation. You might try replacing it with one of the batteries in the simulation bin. It appears (although I am far from sure!) to be objecting to something in the power supply spice model so this may be normal behavior. The simulator is a work in progress. Peter ---
**Author:** ![RAPTOR7762](https://forum.fritzing.org/user_avatar/forum.fritzing.org/raptor7762/32/22620_2.png) [@RAPTOR7762](https://forum.fritzing.org/u/RAPTOR7762)\ **Post date:** [July 13, 2025, 1:55pm UTC](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741/5 "2025-07-13T13:55:02Z")
Hi @leandroding @vanepp I’ll reproduce the sketch to see what’s wrong ---
**Author:** ![RAPTOR7762](https://forum.fritzing.org/user_avatar/forum.fritzing.org/raptor7762/32/22620_2.png) [@RAPTOR7762](https://forum.fritzing.org/u/RAPTOR7762)\ **Post date:** [July 13, 2025, 2:20pm UTC](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741/6 "2025-07-13T14:20:02Z")
OK very strange For me turns up no warning – simulation runs; nothing in multimeter ![image](https://forum.fritzing.org/uploads/default/original/3X/0/c/0c007634e0b90e00605f7fbc3ef840a4a11282f0.png) I’ll recreate it from scatch ---
**Author:** ![RAPTOR7762](https://forum.fritzing.org/user_avatar/forum.fritzing.org/raptor7762/32/22620_2.png) [@RAPTOR7762](https://forum.fritzing.org/u/RAPTOR7762)\ **Post date:** [July 13, 2025, 2:50pm UTC](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741/7 "2025-07-13T14:50:06Z")
I think I found the problem @leandroding @vanepp ![image](https://forum.fritzing.org/uploads/default/original/3X/c/7/c71650767867f97670215ca5efd663f6a7cb550a.png) But that did not change anything. It might be the simulation code in the app Edit: It will not be possible to key in 10µF. @leandroding How did you do so? ---
**Author:** ![vanepp](https://forum.fritzing.org/user_avatar/forum.fritzing.org/vanepp/32/4426_2.png) [@vanepp](https://forum.fritzing.org/u/vanepp)\ **Post date:** [July 13, 2025, 3:13pm UTC](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741/8 "2025-07-13T15:13:50Z")
> [@RAPTOR7762](#): > > It will not be possible to key in 10µF. @leandroding How did you do so? Likely via the pull down menu which will set it. ![capture](https://forum.fritzing.org/uploads/default/original/3X/a/f/afbb5353f0f00c1d0f88e8edbc133d33a44bfcbd.jpeg) I expect the issue is a bad spice entry in the power supply although it is odd that it isn’t flagging the error for you. That is likely why the power supply isn’t in the simulate bin because it doesn’t work correctly yet. Peter ---
**Author:** ![RAPTOR7762](https://forum.fritzing.org/user_avatar/forum.fritzing.org/raptor7762/32/22620_2.png) [@RAPTOR7762](https://forum.fritzing.org/u/RAPTOR7762)\ **Post date:** [July 13, 2025, 3:15pm UTC](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741/9 "2025-07-13T15:15:15Z")
Even then not working. I trialled and error, tried transient mode, but still no ---
**Author:** ![vanepp](https://forum.fritzing.org/user_avatar/forum.fritzing.org/vanepp/32/4426_2.png) [@vanepp](https://forum.fritzing.org/u/vanepp)\ **Post date:** [July 13, 2025, 3:16pm UTC](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741/10 "2025-07-13T15:16:29Z")
Try replacing the power supply with a battery from the simulation bin. I expect that will work. Peter ---
**Author:** ![RAPTOR7762](https://forum.fritzing.org/user_avatar/forum.fritzing.org/raptor7762/32/22620_2.png) [@RAPTOR7762](https://forum.fritzing.org/u/RAPTOR7762)\ **Post date:** [July 13, 2025, 3:20pm UTC](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741/11 "2025-07-13T15:20:31Z")
![image](https://forum.fritzing.org/uploads/default/original/3X/3/5/352c0e23dad84c2347cfad0df998f902c66eea56.png) Unfortunately not… ---
**Author:** ![vanepp](https://forum.fritzing.org/user_avatar/forum.fritzing.org/vanepp/32/4426_2.png) [@vanepp](https://forum.fritzing.org/u/vanepp)\ **Post date:** [July 13, 2025, 3:36pm UTC](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741/12 "2025-07-13T15:36:21Z")
Huh! Does for me. ![capture](https://forum.fritzing.org/uploads/default/original/3X/0/4/04656ff2d5c1f62ab0b266cf5153d539b728a17d.jpeg) I have no idea if it is right or not as I don’t know what the result expected it, but it simulates without complaint and outputs a voltage on the meter. Peter ---
**Author:** ![leandroding](https://forum.fritzing.org/user_avatar/forum.fritzing.org/leandroding/32/25672_2.png) [@leandroding](https://forum.fritzing.org/u/leandroding)\ **Post date:** [July 13, 2025, 5:26pm UTC](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741/13 "2025-07-13T17:26:25Z")
Just insert using Alt+0181 or by typing ‘u’ ---
**Author:** ![leandroding](https://forum.fritzing.org/user_avatar/forum.fritzing.org/leandroding/32/25672_2.png) [@leandroding](https://forum.fritzing.org/u/leandroding)\ **Post date:** [July 13, 2025, 5:34pm UTC](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741/14 "2025-07-13T17:34:29Z")
I believe that using a battery has the same effect as using a DC power supply. The purpose of the circuit is to double the input voltage (Vin), with a maximum output capacity of 24V. So, if a 9V battery is used, the output should be approximately double that. Since the circuit works correctly in another simulator, I will go ahead and report this as a bug on GitHub myself. Thank you all very much for helping me confirm this information. ---
**Author:** ![vanepp](https://forum.fritzing.org/user_avatar/forum.fritzing.org/vanepp/32/4426_2.png) [@vanepp](https://forum.fritzing.org/u/vanepp)\ **Post date:** [July 13, 2025, 5:43pm UTC](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741/15 "2025-07-13T17:43:11Z")
Be aware that the simulator currently only does static simulation (not dynamic unless you enter debug mode and enable it, as it is not complete yet AFAIK.) So you will only get the static dc state which likely won’t include voltage doubling (since that would require dynamic state.) As I said I know relatively little about simulation so this may not be correct, but I think this is likely a current implementation limitation rather than a bug. It may work if you enable the dynamic simulation code under debug (which does do dynamic simulation as far as I know.) I think there is a forum post (a search for simulator or simulation should find it) that explains how to enable dynamic simulation. No harm in opening an issue on github, but I expect you may get a similar answer from someone who knows what they are talking about. Peter ---
**Author:** ![leandroding](https://forum.fritzing.org/user_avatar/forum.fritzing.org/leandroding/32/25672_2.png) [@leandroding](https://forum.fritzing.org/u/leandroding)\ **Post date:** [July 13, 2025, 8:00pm UTC](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741/16 "2025-07-13T20:00:53Z")
Ah, understand know. I am searching for how to enable dynamic simulation and learning about it so I can see if it works or not. Thanks for that information! ---
**Author:** ![vanepp](https://forum.fritzing.org/user_avatar/forum.fritzing.org/vanepp/32/4426_2.png) [@vanepp](https://forum.fritzing.org/u/vanepp)\ **Post date:** [July 13, 2025, 8:09pm UTC](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741/17 "2025-07-13T20:09:45Z")
These two posts may give some help. The first points to the simulator documentation from the author and mine sort of describes in not much detail how to get in to debug mode. > [@Simulation in Fritzing](https://forum.fritzing.org/t/simulation-in-fritzing/13812/2): > > Hello! Maybe there will a simulator soon. I made a super basic one which has been merged in the Fritzing repository (in its own branch), but it has not been merged in the development branch. If you are able to compile it from source, you can try out. If not, you will have to wait until is released (hopefully in 0.9.9, but I cannot guarantee that). It still needs some work and it is an experimental (beta) feature, but it is functional. HOWEVER, the simulator is really limited and it will not be… > [@Simulation not working](https://forum.fritzing.org/t/simulation-not-working/27033/9): > > I think one problem is likely your resistor value on the LED is too high. As it stands at 9V it will only put about 1ma through the LED and LEDs typically need 10 to 20 ma to light, About a 1K resistor should get you to 10ma. That said I still can’t get simulation to work even in debug mode with transient selected (you need to start Fritzing with the -d flag to enable debug mode then select the transient mode (greyed out here because debug isn’t active) in order to get… Peter ---
**Author:** ![fai](https://forum.fritzing.org/letter_avatar_proxy/v4/letter/f/87869e/32.png) [@fai](https://forum.fritzing.org/u/fai)\ **Post date:** [July 13, 2025, 10:38pm UTC](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741/18 "2025-07-13T22:38:53Z")
Hi, The power supply is working in 1.0.5 (official version). It needs an extra file that the simulator needs to find (abalog.cm, available in ngspice distributions). Unofficial binaries (e.g. from Linux repositories) may not have this packed correctly (it is a very beta feature). This circuit needs a transitory simulation, and to setup the time of the simulation properly (using the right time step). To do that, run fritzing with the -d option from the terminal. That will enable the transitory simulation. Then, add an oscilloscope to select the sim time and time step (check preferences menu). And then activate the transitory simulation in the arrow of the sim button. If you do that, you will see the right results (I hope, I did not check the circuit but I get around the double of the voltage). See below ![image](https://forum.fritzing.org/uploads/default/original/3X/d/2/d279565789b169be4cc84c79541e5772e006caa3.png) Andres ---
**Author:** ![vanepp](https://forum.fritzing.org/user_avatar/forum.fritzing.org/vanepp/32/4426_2.png) [@vanepp](https://forum.fritzing.org/u/vanepp)\ **Post date:** [July 14, 2025, 12:11am UTC](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741/19 "2025-07-14T00:11:27Z")
On the official 1.0.5 release from [Fritzing.org](http://Fritzing.org) on Win10 I get the listed error message although apparently @RAPTOR7762 does not. I suppose I could try reloading 1.0.5 to see if that clears it though. Peter ---
**Author:** ![RAPTOR7762](https://forum.fritzing.org/user_avatar/forum.fritzing.org/raptor7762/32/22620_2.png) [@RAPTOR7762](https://forum.fritzing.org/u/RAPTOR7762)\ **Post date:** [July 14, 2025, 1:01pm UTC](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741/20 "2025-07-14T13:01:02Z")
I also git mine from the official release. Edit: In case anyone wondering how to do run fritzing via command line here’s what I did ```bash Microsoft Windows [Version 10.0.26100.4652] (c) Microsoft Corporation. All rights reserved. C:\Users\User>cd C:\fritzing.1.0.5 C:\fritzing.1.0.5>Fritzing1.0.5 # This starts Fritzing normally C:\fritzing.1.0.5>Fritzing1.0.5 -d # This starts Fritzing in Debug mode C:\fritzing.1.0.5> ``` Your’s may be a little different as my file structure is like this ![image](https://forum.fritzing.org/uploads/default/original/3X/0/1/01d9b768cb247c5615b65efec865cc4f2bb08332.png) @leandroding Hope mine and Failiz’ message helped! [Next page](https://forum.fritzing.org/t/555-timer-astable-multivibrator-simulation-help/29741.md?page=2)