Falstad Circuit Simulator 1.5i is a java based online tool for creating and simulating electronic circuits.
The applet consists of a simple easy to use interface and comes with a library of example circuits to which standard components can be added and altered to create almost any circuit. Circuit animations can be turned on and off to indicate current flow, voltage, power, etc, allowing users to experiment and see the effect of changes they make to the circuit. This makes Falstad not only a good tool for drawing circuits but also testing and explaining electronic principles.
This tool can be usefull in the design and testing of electronic circuits. The example circuits can be altered, or a circuit can be made from scratch. Advantages are that no electronic equipment is needed in this phase and nothing can go wrong, so endless possibilities can be tried. If you are not very good at electronics yet, the example circuits can teach you a lot about the components and their purposes.
Use (step by step)
1. If you click the link, the simulator will start in a pop-up window. It's a java applet so a plug-in is needed.
2. Choose one of the example circuits, or start with a blank screen via 'circuits' in the task bar.
3. Right-clicking in the screen gives you a menu with parts you can add.
4. Drag your mouse for placing the part.
5. You can edit a part by right-clicking it and then clicking 'edit'
6. By moving your mouse on a wire or part of your circuit, you can see the current, voltage, etc.
In our PAP project we use a circuit to connect a sensor to an arduino microcontroller. We use rotation sensors (inclinometers) to measure a riders position on a horse. In this application there is a lot of noise caused by the up and down movement of the horse and rider. We filter out this noise using a low-pass filter, which is an RC-circuit to filter out high frequency voltage changes and keep the low frequencies. The cutoff frequency of a low-pass filter is determined by the resistor and capacitor: fc = 1 / (2piRC). To play with the values of the resistor and capacitor, the Falstad Circuit Simulator is a suitable program.
Because a low pass filter is an often used type of circuit this is one of the standard circuits in the program. We opened this circuit.
We changed the values of the resistor and capacitor. Also the values for the input can be changed. In the output you can immediately see what the effect is, on the bottom left you see the input, on the right the output.
The advantage of using a program is that you don't need any hardware in the testing phase. Once you know which components you will use (for example which combination of values for resistor and capacitor works best) you can buy them; in stead of having to buy more. You don't need testing equipment like oscilloscopes etcetera. In this case it's an example of a pretty easy circuit and the values can also be calculated using the formula, but for more complex problems it is a good way to try things out.
One notable drawback of the applet is the inability to print the circuit drawings in an easily readable format. A function to save as a .jpg for example would be handy for including the circuit in documentation.
Sensors and actuators (e.g. an LDR or a motor) are not included in the program. This would be a useful addition for many design engineering purposes.
Directions on how to use the tool, and information about the example circuits:
Falstad has more simulators for physics and math. Some of them might be usefull for your design project as well:
Alternative Circuit Drawing tools.
While Falstad was the only free online circuit drawing tool we were able to find a number of alternative software packages are available for free or commercial download. Including;
X-Circuit - a UNIX/X11 (and Windows, if you have an X-Server running, or Windows API, if not) program for drawing publishable-quality electrical circuit schematic diagrams and related figures, and produce circuit netlists through schematic capture. XCircuit regards circuits as inherently hierarchical, and writes both hierarchical PostScript output and hierarchical SPICE netlists. Circuit components are saved in and retrieved from libraries which are fully editable. XCircuit does not separate artistic expression from circuit drawing; it maintains flexiblity in style without compromising the power of schematic capture.
TinyCAD - TinyCAD is a program for drawing circuit diagrams commonly known as schematic drawings. It supports standard and custom symbol libraries. It supports PCB layout programs with several netlist formats and can also produce SPICE simulation netlists.
Solve Elec - Freeware program for MAC and Windows to draw and analyze electrical circuits.
Electronics Optimizer - Electronics design tool for advanced optimization and design of electronic circuits - with Optimizer, Monte Carlo and Worst Case Analysis.