I started to work with some new FPGA-design software that seemed to take a long time to "build" a simple LED-flasher demonstration project. I let it run for about 45 minutes while I answered emails and had a conference call.

When I took another look, I saw something flash in the corner of the software's display area, but it appeared only briefly every 15 seconds or so. That made it impossible to see what the short message said. The message also appeared superimposed on other information, which increased the difficulty to read it.

That's when I thought about using my camcorder to record the display so I could play it back and see what the message said. I recorded about 15 seconds of video, loaded the video into my iMac's iMovie software and slowly scanned through the frames. Then I saw the brief superimposed image of "Scanning JTag ports..." and figured the FPGA software was hung in a loop. I restarted the software and built the FPGA project without problems. I hadn't thought of a video camera as a debug tool, but it worked nicely in this care.

I suppose a still camera could work equally well in some situations that provide an external trigger signal. Many film cameras and photoflash units used to provide a connection for an electrical trigger, but I'd bet most small digital cameras do not.

My first "exposure" to test-result photography involved a Tektronix oscilloscope, circa 1977, and a camera attachment that used Polaroid "instant" film. As best I can recall, I set the scope's trigger, opened the camera's shutter, ran a test, and the camera captured the scope's trace on the fly. During several weeks of experiments, I went through many packs of film.

After engineers took similar photos, they had to extract the information from the trace or traces with a ruler and then convert the information into useful units. Some lucky engineers had a Gerber Variable Scale, basically a precision spring with graduated marks so a user could set the full-scale point and then directly read off the scaled values. You can read more about the Gerber Variable Scale at: www.nzeldes.com/HOC/Gerber.htm. From time to time, Gerber scales show up on eBay. If you admire older measuring and calculating devices, the Gerber scale is worth adding to a collection. --Jon Titus