PC Boards the Easy Way

My latest homebrew project is a “universal” interface to connect the computer, the HF radio, the headset and the footswitch together in such a way as to allow logical audio path switching and level control, along with DC isolation (transformer coupling) of the audio signals. For example, my homebrew contesting software allows voice messages (CQ, exchange, etc.) to be stored on the PC hard drive instead of in an outboard voice memory device. Hitting a function key to start a message also activates the serial port's DTR lead. The interface uses this signal to activate the PTT as well as switch the radio's mic input from my headset mic to the PC's audio output. There is also an override that locks out the PC message if I momentarily hit the footswitch. The interface performs other tasks, and supports CW and sound card digital modes as well.

The interface is housed in a relatively small sloping panel enclosure. The original circuit board was a 3.2” x 4.6” perf board, which was sufficiently large for all the components. The enclosure mounts 10 rear panel jacks, two front panel jacks, four volume controls, and three switches. As you can well imagine, the wiring that connected the perf board to all the chassis-mounted components made the inside of the enclosure look like the proverbial “rat's nest.” The photo below shows the prototype, removed from the enclosure. The component side, with all the connecting wires, was even uglier.

I wanted to change a couple of components in the next version (there may never be a “final” version), and was overwhelmed at the thought. I felt it would be nearly impossible, given the small enclosure size, to successfully re-solder the 20+ connections after they were unsoldered or clipped to allow removal of the perf board. And connecting a voltmeter or `scope lead to a component on the board to troubleshoot? Forget it, you could hardly even see the board beneath all the wiring!

The conclusion was obvious. The next version would need a real printed wiring board instead of a hand-wired perf board. Now, how should I obtain it?

In searching the web and Googling “printed circuit boards” I came across a company that offers a seamless, moderate-cost solution for the experimenter and even for someone needing a small production run of PC boards. The solution starts with their free downloadable PC layout software and ends with online ordering and rapid delivery of two prototype boards. You can specify 2-layer or 4-layer boards, and they come with plated-through holes. Try doing that at home! My two 2-layer boards cost less than $80 total, and were in my hands less than a week after I completed the design and e-mailed the resulting design file and order form.

The company that offers this service is ExpressPCB. Their web site is, naturally enough, expresspcb.com. Pages on the site describe “how it all works” and “how much it costs” among other topics, and there's a link to download their ExpressPCB software file. This is a 9.3 megabyte file, so you'd better have a broadband internet connection or a LOT of patience.

Installation of the file was straightforward and without glitches on my garden-variety Win-XP machine. Once installation is complete, you have two executable files: expressPCB and expressSCH. The second program lets you create schematic diagrams, which I didn't use. Each program also has its own brief but adequate HTML tutorial.

For being free, their software is quite impressive. It allows you to design 2-layer as well as 4-layer PC boards in whatever size you need. There are over 300 components (capacitors, ICs, on-board connectors, SMT devices, etc.) in the component library. You can also create your own custom components and place them wherever you want on the PC board. There are around 100 different pad styles and sizes for through-hole and SMT devices. You can specify and mix any of 17 trace widths, from .007 inches all the way to .25 inches.

The photo above is a real “screen shot” using my inexpensive digital camera to photograph the LCD monitor. The blurry image and non-linearity is due to the camera.

The software shows traces on different layers of the board in different colors, and even the silkscreen layer (showing component outlines plus any text you wish to have on the board) has its own color. Layers can be displayed or hidden in any combination. It's very useful to hide all but one layer to verify that there are no inadvertent trace crosses. As is usually necessary in all but the simplest PC board design, one or more segments of a trace can be moved from one layer (side) of the board to the other, and the software automatically places the necessary “via” to connect the two sides. As previously mentioned, all pads and vias have plated-through holes.

You have almost unlimited instant zoom in and zoom out capability (example shown above) using the plus and minus keys or the wheel on your mouse. This feature lets you view a small area of the board, to confirm spacing between adjacent components and traces, and accurately place these items. Then zoom back out to look at the overall board layout. The design file (filename.pcb) is quite small.

I started to write a narrative on the process of laying out a PC board, but realized it's not possible to do it in a reasonable amount of space. Instead, I suggest you go to the ExpressPCB web site, download their free software, and play with it. Create a relatively simple design so you can learn the process of adding components, pads and traces, and modifying the design. Afterward, if you have a project that you've been thinking about, get out its schematic and use the software to design a real PC board.

Once you've finished your design, you can obtain a price within the software application itself. You don't need to go to their web site or provide any kind of information. The minimum order is two prototype boards or four production boards. The prototype boards will be less expensive because they don't include any silkscreen component outlines or text, and no solder mask.

If you want to make a purchase, their web site offers secure online ordering, with credit card payment. Just specify the name of the file you want made and it becomes attached to the emailed order. The price includes second-day air shipment. I emailed my order Thursday evening just before the Easter weekend, and UPS delivered the boards the following Tuesday. I didn't talk with anyone at the company; this process is truly streamlined as well as seamless.

The end result was a professional-quality PC board, and a much neater “universal” interface for my station. You can bet I'll be using them again when I'm ready to build another project that requires (or can benefit from) a printed circuit board.

(Full Disclosure: I have no relationship with this company. Other than emailing my order and receiving automated order confirmation and ship confirmation emails, I have had no contact with them.)

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