Program with Integrated Circuit Emphasis (SPICE) has been around since 1973. The basic computational engine has
always been open source. It began as a simple analog circuit simulator that took a structured text file as the
input net list and provided a text file output that contained the calculated values that the user specified such
as DC bias points, transient analysis, and AC analysis. Component models started with relatively simple definitions.
If you wanted a graph of the response, it was in the form of text characters with a standard 80-column division
on the y-axis and the x-axis was as many divisions as it needed to be to cover all the points calculated (often
printed out on fan-fold paper in a pin printer). Yes, I personally used those versions in the mid 1980s.
PartSim Schematic Entry Screen
As time progressed, improvements were added to the computational engine to handle a wider range of component
models including digital and RF/microwave. More parameters were added to component models to yield a better agreement
between simulation and laboratory measurements. Lagging the mathematical sophistication was development of a graphical
user interface (GUI) for building circuit schematics rather than needing to enter all the circuit nodes and component
parameters manually into a text file. Trying to keep track of node numbers was a real challenge for all but the
simplest circuits. Early attempts at a GUI were cumbersome and did not provide a seamless interface between schematic
entry and simulation and graphing. Eventually really good solutions came to the market. Most of the modern circuit
simulators are based on SPICE, with proprietary add-ons in the computational engine. User interfaces have gotten
really nice. The more you're willing to pay, the better the interface and the calculation capability.
PartSim Transient Analysis Screen
Online simulators are now going through the same kinds of growing pains that the earlier iterations of PC-based
SPICE simulators experienced. Most are really clunky and always seem to be missing key features and/or easily
accessed features - like rotating components on the schematic or routing interconnect lines. Aspen Labs has a
free online analog circuit simulator called PartSim that
seems to have conquered most of the basics. Being able to save and recall your work is a huge benefit. However,
it appears that the file is saved on the website server rather than on your local machine, so privacy and security
issues might prevent a few users from using such a service regardless of how good it is. I have recommended online
tools to people in the past and have been apprised of the proprietary information problem. Still, most users probably
will not care. One advantage of the online storage is that it is effectively a 'cloud' environment where you can
access your circuit file from anywhere that has an Internet connection (after signing in with user name and password).
PartSim Report Screen
I loaded the example files and played around with them enough to know that
PartSim is just what the hobbyist and casual professional
designer can use. Simulation time and switching between screens is slower than with a local program, but that
is more a function of your Internet connection than of PartSim's host server. There is no sense in me reiterating
what has been written a thousand times about how to enter circuits and set up and run simulations, so instead
I refer you to the seven short online video tutorials to
help get you started. There are some not-so-obvious features that makes it worth your while to view them. If you
are not the type to read instructions, just remember to right-click and double-click on everything - including
interconnect lines - to find all the options available to you.
PartSim Bill of Material (BoM) Screen
I could understand the need if it was an astronomy simulator with
but this is puzzling.
These items are an archive of past Topical Smorgasbord items that have appeared on the RF Cafe homepage. In keeping with the "cafe"
genre, these tidbits of information are truly a smorgasbord of topics. They all pertain to topics that are related to the general engineering
and science theme of RF Cafe. Note: There is also a huge collection of my 'Factoids' (aka 'Kirt's Cogitations') that might interest you as well.