Analog Tips & Tricks

Are you looking for ways to improve your analog and RF circuitry? Engineer Ed Nisley provides a few tips for getting started. He shows you how easy it is to take your PCB wiring skills to the next level. Who knows, your digital projects just might improve too.

Circuit Cellar has always attracted readers who enjoy building gizmos, both at work and for their own use. My December 2004 column, “Building Boxes,” prompted enough comments and suggestions regarding additional techniques that I decided a follow-up was in order.

Although these tricks are designed to improve your analog and RF circuitry, even your digital projects will benefit, because digital is just analog with the gain cranked way up. You’re sure to find at least one technique that will make your next project work better.

I wire most of my projects on PCBs built in my basement shop, using a process that produces both circuit documentation and reasonably high-quality hardware without too much effort. I’ve come up with some tricks that should help you get good results too.

I use CadSoft’s EAGLE schematic capture and board layout software, which runs on Windows, Linux, and Mac OS X (www.cadsoftusa.com). The free version can handle most of the circuits in this column, and the Standard version is reasonably priced. EAGLE is perfectly stable on my SuSE Linux 9.2 desktop system. The board layout program can produce output files in nearly any format, including the Gerber files used in board production shops. I save the output for each layer as a Postscript file, and then import the files into the GNU Image Manipulation Program (GIMP) image-editing program at 600 dpi.

The top image is the top copper layer from an EAGLE board design. The bare board shows several flaws, but the one on the bottom came out fine. The ruler scales are 0.050″ vertically and 1 mm horizontally. The board has extremely small features!

The top image is the top copper layer from an EAGLE board design. The bare board shows several flaws, but the one on the bottom came out fine. The ruler scales are 0.050″ vertically and 1 mm horizontally. The board has extremely small features!

The top image in Photo 1 shows the copper plane pattern for the charge pump LED power supply I described in my April 2005 column. I panelize them with the GIMP to produce a single image with multiple patterns in a rectangular grid. Because all this happens digitally, there’s no loss of resolution and no smudges. I then print the image through an HP LaserJet 1200 on a sheet of toner-transfer film from either Pulsar (www.pulsar.gs) or Techniks (www.techniks.com). It turns out that toner contains a thermoplastic that both adheres to bare copper and resists the etching chemical solution.

Because most of my boards are extremely small, they don’t fill a complete sheet of the toner-transfer film even after I panelize them. I print a sheet of paper, tape a square of film that’s approximately 1″ larger than the patterns atop them, and then run the paper through the printer again. The adhesive on cheaper tapes tends to melt at laser printer temperatures, so use good tape and monitor your results. Put a single strip on the leading edge of the toner-transfer film to allow the paper and film to shift slightly as they pass through the fuser rollers.

This article first appeared in Circuit Cellar 181. You can read the entire article here.

Ed Nisley is an electrical engineer, author, and long-time Circuit Cellar columnist living in Poughkeepsie, NY. His column “Above the Ground Plane” appears in Circuit Cellar every other month. You can contact him at ed.nisley@pobox. com. Write “Circuit Cellar” in the subject line to avoid spam filters.