My experience with the Internet goes back to the mid-1980s, when transactions using FTP file transfers, Telnet sessions, and SMTP mail transfers were the rule. This was before the advent of the Web browser and today's ubiquitous commercial World Wide Web. Those days were characterized by a lot of file sharing. Folks swapped executables and source code regularly. The best things in TCP/IP life were free.
Fortunately, the spirit of open-source and free distribution is still very much alive and well on the Web, in spite of the preponderance of commercial sites, the eBay phenomenon, and the like. Just last week I discovered some free and open-source code engineering applications that confirmed the good old days are still here.
The first discovery is a Windows design entry and schematic capture program called TinyCAD. Coming from UK-based author Matt Pyne, the TinyCAD application installs from about a 2.5 Mbyte executable with, perhaps, another few megabytes of component libraries.
In use, TinyCAD provides an efficient user interface that lets you place components on-screen, connect them with your mouse, insert reference designations and values, and check for design-rule infractions. It also supports multi-sheet schematics for partitioned projects, joining nets across sheets.
After tinkering with a few supplied sample circuits, I started to use the program in earnest, capturing a schematic of a voltage-to-current converter circuit I've been thinking about.
Until now, I've been using the venerable Electronics Workbench product called MultiSim for an occasional SPICE simulation under Windows. MultiSim (available these days from National Instruments Electronics Workbench Group) supports schematic capture, straightforward pushbutton simulation, and lots of virtual test equipment icons. It also gives you board layout tools and integrated test hooks.
I've been a happy MultiSim user for years. However, although MultiSim sidesteps the tedium of annotating diagrams for SPICE runs, it doesn't create a clean easy-to-read schematic that you’d necessarily want in a finished document. Also, MultiSim, and its related MultiRoute auto-place-and-route package, is priced anywhere from about $1500 on up, and that price tag could be a tad stiff for single-seat shops or hobbyists.
For creating great looking schematic documents I prefer Cadence's popular OrCAD package. Like MultiSim, it's kind of pricey too, starting at about $1700 for an entry-level OrCAD implementation. Also like MultiSim, OrCAD can be used to capture schematics for analog and digital circuits. It can also help you design using digital HDL (high-level description language) modules, and you can use it to verify a design.
It turns out that open-source TinyCAD can do quite a bit of what the top-drawer EDA programs do, and at no monetary expense. A small investment in time is all it takes to ascend a short learning curve.
TinyCAD lets you draw circuit diagrams using supplied libraries, or components of your own, crafted with a built-in component library editor. You can also import libraries from files on the Internet and there's a sizable TinyCAD Yahoo group.
If you log on there, you can access free library elements that others have created.
Once you've captured your schematic, you can use TinyCAD functions to automatically add symbol references, check design rules, and create parts lists. TinyCAD also exports netlists into printed circuit board layout programs. Design elements can be copied and pasted from the Windows clipboard into other Windows packages, such as Microsoft Word.
Like its big brothers OrCAD and MultiSim, TinyCAD packs a Spice template engine that lets you add Spice output to any symbol. No formal Spice symbol library is supplied, but there are examples of Spice libraries at the Yahoo forum. The package's Spice template engine can also generate Spice files for almost any Spice engine, and there are a lot of those out there for the asking, too. A good one is Spice Opus for Windows, Linux, and Solaris operating system platforms.
At the tail end of the process, TinyCAD supports a variety of net-list formats for board routers. A freebie is FreePCB.
You can also marry TinyCAD files to Protel, PADS, and Eagle SCR board formats.
For its part, FreePCB is an open-source circuit board editor that runs under Windows, based on the popular GNU General Public License. Although it doesn't include an autorouter, it can be used with a Web-based router called FreeRoute.
FreePCB can accommodate single-sided boards, or up to a whopping 16 layers, and will help you craft packaging panels as large as 60 inches square. You can also import and export netlists from the popular PADS-PCB package. There's more: you can use FreePCB to export extended Gerber files and Excellon drill files.
Some of the best things in engineering life are still free, aren’t they?
