Circuit simulation can be used to try out circuit configurations before (instead of) buying components and soldering.
It can be free (or you can pay for a simulator)
You can iterate rapidly
Waveforms can be observed at many nodes simultaneously without instrumentation inaccuracy or the test gear affecting the circuit
Most manufacturers make simulation models (usually Spice) available for their semiconductors.
It follows the "garbage in garbage out" principle, it is only as good as the models you feed in.
List of free Spice type simulators and where to get them
- Simetrix - Free cut-down version of the commercial product is limited to 150 nodes, scripting is disabled, but all else is fully working - Save, print, import 3rd party models - comes with extensive libraries of common parts, and circuit examples. Download from http://www.catena.uk.com
- SwitcherCAD/LtSpice - Spice version, dedicated to Linear Technologies' switch mode power supply chips. It includes hard-coded models for their switcher components which speeds up simulation. Can be used as a conventional Spice simulator, from http://www.linear.com/designtools/software/switchercad.jsp
- PSpice - watch this space
- TINA-TI - Easy-to-use, but powerful, circuit simulation program based on a SPICE engine. TINA-TI is a fully functional version of TINA, loaded with a library of TI macromodels plus passive and active models. Download from http://focus.ti.com/docs/toolsw/folders/print/tina-ti.html
Other free simulators
- PC-ECAP - Will calculate and plot: gain, phase, group delay, impedance, VSWR and return loss. This versatile program can also calculate your circuit's transient response, using one of eight waveforms. Shareware DOS program that requires DOSBox to run on Windows Vista. Download from http://www.cdquickcache.com/pcecap.htm
- ScanTesla - Computer modeling of Tesla coils. See ScanTesla or download here http://drsstc.com/~sisg/files/scantesla/
- Barry's RLC Simulation - Simulates a dry fire of a coil gun without projectile, very useful as a starting point to decide on design parameters. http://www.coilgun.info/mark2/rlcsim.htm
- Falstad Java circuit simulator applet - Animates circuit behaviour graphically. Handy to visualise the basics, or just play with it and be mesmerised by the moving dots and changing colours. http://www.falstad.com/circuit/