Using Falstad's Circuit Simulator





Introduction: Using Falstad's Circuit Simulator

About: I'm a student from Cheshire, currently studying at University of Nottingham!

Here, you can learn how to use Falstad's Simulator. This is a java based simulator and can be founs at:
Circuit Simulator]. (Sorry for the bad quality screenshots)

Step 1: Basic Controls

When the program is first opened, the starting circuit is a simple LRC circuit (This stands for Inductor, Resistor, Capacitor. These are the main components of this circuit).

When the program is opened on the screen, the buttons on the toolbar are:
File - Import, Export, Exit

Scope - Stack All, Unstack All

Options - Show Current, Show Voltage, Show Power, Show Values, Small Grid, European Resistors, White Background, Conventional Current Motion

And finally, Circuits - To list all of the seperate circuits would be quite pointless as there are loads of them (See for yourself if you dont believe me!) These circuits come with the program that the creator must have pre-programmed in.

Step 2: Selecting Different Components

When you are wanting to make your own circuit, you can select the components you want to use such as a resistor. This can be selected by Right Clicking in an area where there are no wires etc. Then selecting "Add Resistor". Most of the other components are in sub-menu's e.g.

Right click > Passive Components > Add Push Switch

After the component has been selected, you click and drag in an empty space for where you want the component to be. (The component can be dragged to different sizes.)

To join different components, Right click > Add Wire. Then, if there were to components such as a Resistor and Capacitor, you would go from one of the legs of the resistor, to the leg of the capacitor that you would want to join. When you are dragging the wire, on each of the capacitor/resistor legs, a small circle will appear as this is where the wire would join to.

The circuit in the picture is a simple LED, resistor and power supply circuit.

Step 3: Using the Scope and Editing Components

If you want to see the waveform, current consumption, power or voltage, the scope tool can be used. This can be used on most of the components excluding some such as Triodes. To see a components waveform in the scope, you can right click the component and select "View in Scope".

Once the component is in the scope (At the bottom of the program), you can select what is viewed in the scope such as if i use the LED for example i can make the scope view its Current by right clicking the scope at the bottom and deselecting "Show Voltage". This will show only the current; as "Show Peak Value" is still selected, this allows you to see the peak amount used by the LED, this can be useful if designing PWM circuits etc.

To Edit a component such as a Resistor, right click the resistor and go on "Edit". A small box should appear which in it says: Resistance (ohms) with a box next to it and a slider bar underneath. The desired resistance can be put into that box to change the components resistance. This box varies with each component.

Step 4: Saving Circuits

To save a circuit that you have made go:
File > Export > (Copy the code in the export box) > (Paste into a .txt document or similar) > Save the code.

When loading a circuit:

Find the .txt (Or similar file) > Copy the code > (File > Import) > If there is any code in the import box, clear it and paste your code into that box.

Step 5: Choosing a Premade Circuit

To choose a premade circuit: (Example circuit of 555 Square generator)

Circuits > 555 Timer Chip > Square Wave Generator

This should come up with a circuit of a 555 based square wave generator.



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I have used the offline circuit.jar simulator for last 5 years or so but recently after an update, probably of Java, on my computer it has stopped working. The initial screen would show the LRC circuit. After a blank circuit I cannot add anything. Moreover, previously I could simply save/open my data files (without import/export) but now not possible.

Has anybody faced this problem and got any solution?

Good Simulation S/W but a limited components . I need to draw a circuit with PWM with components

PIC16F877A ,SG1524 , LM324 .

But I couldn't add them

Is there other way to add them ?


its an awesome software that allows changes on the fly

Hi everybody, what about the option to use mic and speaker? You can choose them from the menu but with no response

Thank you. I was experimenting with the Falstad circuit simulator and "built" a virtual copy of a circuit I have used with actual parts in order to understand better how and why it works. I had some unanswered questions about how to save a circuit in Falstad and you answered them.

Great program from Falstad, many thanks guys. Ive'd been using it for sometime now time in my lecture and circuit simulation. Does anyone out there know how to include speakers in the circuit? Thanks

1 reply

Hey, because each speaker is different, it will have different parameters. Plus, a speaker varies its parameters through frequencies but I think (simulating one frequency peak) you could do something like: Resistor - LC Bandpass filter. For example! For an 8Ohm speaker (5"), with a resonance peak at 320hz, you could have the simulation parameters of: 6R resistor - 10u capacitor and 22mH inductor in parallel. (I know this isnt an ideal model and whether it should work like a speaker but going off knowledge, it had the resistor for the resistive impedance and a band-pass filter set to 339.32Hz. This should really have a resonant peak at that frequency but I think its only a 6db/oct filter?:S im not sure but good luck none the less! :D

Does anybody knows how to build logic for Normally closed relay in falstad circuit.

Thanks in advance.

There is another version out in which we have keyboard shortcuts and can copy and paste components (use ctrl + v, since the right-click menu has no paste). In addition, we can select groups of stuff, move them, and cut copy paste away!
This would have been good to have when I was simulating my homemade microcontroller, which involved a 16-to-1 demultiplexor.....

1 reply

There are also relays! Yum.

Wait, did you say there were triodes (as in, vacuum tubes) in the available components? I have a version of it (simulator) on my hardrive, I use that thing for lots of stuff, but it doesn't seem to do MOSFETs or transformers right. It just freaks out when I try to do a joule thief circuit. And I crash it all the time with my simulated microcontroller. I never knew that there was somebody else on instructibles that knew of this....

4 replies

Yeh, i know about the joule thief circuit. I have tried that circuit myself and it doesn't seem to work. On the current version of the simulator, you can get tiodes now, :D. For transformers, the only main part is the inductance. Also, you need to remeber that if its a step-down transformer, the ratio has to be below 0. That way it works for me :D

Oooooh! Triodes! I'll just have to update then... :-)

I've been using the newest version and... The potentiometers are awesome! They are awkward to resize/place, but they are handy! Too bad the scope probes were taken out in this next version. The zener diodes... about time! I've had to make an equivalent using a couple of opamps and some resistors.

i knew of this as well, and crash it all the time.

You did a very good thing here. I never heard of this fantastic application and you have explained the basics clearly. Thank YOU.

1 reply

Hi, thanks for the reply! Glad you found it useful, thank you again.

Yea that site is fairly useful but I cannot figure out if you are able to change the values of transistors beyond the HFE. like modify the saturation voltage and voltage max. some projects that I'm working on need very specific voltage limitations

This is too cool! I will use this in the next few months.

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Thanks!! First instructable lol