Simulating flip-flop


were any of you able to simulate flip-flop circuit with NPN transistors and LEDs? If yes, can you please show me your solution, thanks :slight_smile:

I believe the simulator is only doing dc analysis at present and likely currently can’t simulate a flip flop.


I am extending the simulator for transitory analysis, but it could take a few weeks and a few months until is released (if everything goes well). In any case, we would also need a spice model of the flip-flop. If you have one, please, share it.

He said simulated with transistors. That would need a spice model for each of the components used to create the flip flop.

If you want to do the simulation before it is ready in Fritzing, a google search for “online spice transient simulation free” gives some alternatives. A quick glance says that is pretty much all spice based as well.

Yes, you can use Kicad, LTspice or falstad for now. You can also use Fritzing to build the circuit and then export the spice netlist. That netlist could be used to load it in any spice-based simulator.
By the way, I made a flip-flop circuit in my development branch and it works as expected using the devices in the core (transistors, resistors, etc.).
This is the output:

Any feedback is appreciated.

Presumably the transistors are not the generics (because I expect the generics don’t have spice models although I may be wrong!) At least the generic npn doesn’t appear to have a spice model. I expect the OP is using the generic transistor (not being aware that it doesn’t have a spice model) and that is why it doesn’t work. If I didn’t know the structure of parts I would not have thought that the generic transistor doesn’ t have spice model (and most users aren’t going to be aware the simulator needs them!)



The generic devices (the ones supported) in the core have spice models that try to match “normal” components. It would be too difficult for electronic beginners to have to add the model to use the simulator.

So, you can use Fritzing 1.0.1 to export the spice netlist, but you cannot simulate it yet unless you build my development branch from source.

Yep, my bad I looked at an old instance of the transistor. The current 1.0.1 parts fzp indeed has a spice model. Sorry about that!