Open-source electrical engineering design tools (continued)

-August 02, 2013

A while back I wrote about some Open-Source Electrical Engineering Design tools.  Several of you chimed in to add some even more highly useful tool ideas.  The short summary of the blog is that some excellent tools exist for doing simple EE design for test and measurement: KiCAD for schematic, LTSpice for simulation, FreePCB for layout and anyone you trust for printed circuit board (PCB) manufacture (I use Advanced Circuits).  Some readers contributed some great additions, including PCB prototyping options Sunstone Circuits and OSH Park.

When doing EE design, using a schematic capture program (rather than just making a schematic in my notebook) is a good idea for everything but the simplest circuits.  As I continue to grow as a designer, I find myself going to schematic capture sooner and sooner in my design process.  Simulation is a wonderful tool, and also something I'm using more often as well.  However, that is where it's stopped in the past.  Board layout takes too long, and printed circuit boards are cheap in high volumes but sometimes rather expensive for only the handful of boards that I need.

I think I've found the last two critical pieces of the puzzle: autorouters and cheap PCB specials.  Now I have a simple path to create a schematic, simulate it (if I need), do the layout quickly, and get inexpensive PCBs.

I recently gave the KiCAD layout tool a try and I love it.  Both KiCAD layout and FreePCB are definitely up to my needs of creating simple 2 and 4 layer boards for test and measurement.  It's good to have options and I like the integration of KiCADs schematic capture and layout tools.

It turns out that I made a huge mistake a few years ago by discounting the FreeRouting Auto-Router.  I have no idea how well it worked in the past, but it did the job for me very well this time.  As always, my designs are usually fairly simple data acquisition, signal conditioning, test and measurement systems, so these tools may not work for more complex designs, but they worked superbly for me.

KiCAD layout has an auto-placement feature to put the components in place that didn't work that well in my case.  However, placing the components myself was quick and easy.  After that the auto-router took over and routed almost the entire board.  I did the last bit of cleanup myself and the board turned out great... and very fast.  So much for the time-consuming layout process.  Here's a FreeRouting tutorial that I found very useful.

With my auto-routed layout complete I, once again, needed to purchase boards.  PCB are incredibly cheap in large quantities, but for low volumes the setup can make the per board costs very high.

A bit of shopping around and some great reader comments (thanks again guys) has generated some options.  My favorite vendor of the past is advanced circuits and they have a pair of specials that help out a bunch.  They offer seriously reduced prices for boards with only copper, no solder mask or silk-screen.  However, I prefer full boards, so their $33 per board (minimum 4) special for 2-layer boards is my favorite.  That means for $132 I get 4 boards, up to 60 sq. in. each in 5 days.  Not bad.

Similarly, Sunstone Circuits offer ValueProto boards, which are 2 layer boards with no minimum order.  A single 1 sq. in. board costs $28 with prices increasing with board size and quantity.  Delivery time is 2 weeks.

A different take on it is OSH Park.  OSH Park is a service that groups orders from different customers together and makes larger PCB orders from them.  They charge $5 per sq. in. for 2-layer boards and $10 per sq. in. for 4-layer boards.  Delivery time is usually 3 to 4 weeks.
Unsurprisingly, each one of these specials has limitations on the design, such as drill hole size, vias per sq. in., board shape and many others.  But, most of my designs are simple enough that I meet the requirements without even trying.  Nonetheless, check out the rules before you start layout.

Thanks to these tools, I see even more custom PCBs in the future of my tests and measurements.  Have you tried these, or other, EE tools?  What EE vendors do you prefer?  Please comment below, as I'm off to quickly crank out another electrical test system.

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