Everything for Electronics
Posted in: Developing Perspectives (March 2012)

Don’t Cut The Blue Wire — Or Is It The Red Wire?

By Bryan Bergeron

I don’t know about you, but other than consistently using red and black for (+) and (-) DC power, respectively, I don’t usually care about wire color. What I do care about is varying the color of wire from one connection to the next. I avoid working from a single spool of wire because that would make visually tracing the resulting circuit difficult. Visual is the key word here. I keep an inexpensive digital camera on my workbench and document most projects with a dozen or so high resolution images.

In addition to photographs, I document my projects with a rough hand-drawn schematic that I later feed into my scanner. However, the schematic — whether in traditional paper form or as a PDF — provides only one limited view of a circuit. A schematic is handy if you have a circuit in front of you, and you have a DMM or other means of tracing the connections and signals. In contrast, as a record of how to build a device from scratch, most schematics fall miserably short. Consider that schematics often bear no resemblance to the physical circuit. For example, a microcontroller chip with dozens of connections might take up most of a schematic and yet consume less than 10 percent of the real estate on a circuit board.

In addition to photographing circuitry, I use my camera to capture metalwork such as cutouts on panels for switches and potentiometers. It may seem trivial now, but seven or eight months after you’ve finished a device — when you’ve forgotten how you managed to mount everything in a small aluminum chassis — you’d give anything for a visual record of how you mounted the devices, the length of the standoffs, and other forgotten details. Lacking the photos, you’ll have to repeat the original trial and error fitting process.

In essence, creating a photographic record is like replicating one of the better articles in Nuts & Volts – lots of close-up images. But whereas publication space is limited, digital images are easy to store and index. When you need to replicate a circuit, just open the file folder and review the images. Need to share a design with a friend? Email the images along with the schematic. Or, post them to the Web.

Another tool in my documentation arsenal is Fritzing: an open source documentation/sharing/teaching program from the University of Applied Sciences Potsdam, Germany (Fritzing.org). The free software is especially useful for documenting Arduino projects, in part because Arduino boards are included in the editable parts library. It’s worth checking out the website and downloading the easy to learn and use software to your PC, Mac, or Linux computer.

In brief, Fritzing is a circuit board design package on steroids. There’s a schematic view and a PCB view. An autorouting function converts your schematic into a circuit board.

And — as with other circuit board editing packages — you can send the resulting file off for production. However, because the service is based in Germany, it’s not cost-effective in the US for single board runs.

What makes Fritzing especially useful is the third breadboard view. In this environment, you position realistic looking components on a breadboard. The software takes care of converting the breadboard to a schematic and PCB. The downside of this software — regardless of how powerful — is that it’s typically useful only after the fact, once you have a rough prototype in hand. That’s why most of my prototype work is documented with a rough schematic and lots of photographs.

If you decide to use a camera as well, don’t forget to make your layout visually apparent. Use internally consistent colors for power, signal, ground, and a variety of colors for other connections. And take photos at major stages along the way, as opposed to only at the end. Happy shooting! NV