Digital camera subs as a scope camera

Allen Moore, Redmond, WA -- EDN, 12/9/1999

A digital camera can be a handy substitute for an oscilloscope camera for older scopes that cannot output hard copy or digital data. A digital camera provides instant results and allows you to easily enhance the image and then add it to reports or Web pages.

If the scope has an illuminated graticule, turn up the illumination. A tripod is useful for repeated shots but is otherwise unnecessary. Position the camera and adjust the camera's zoom so that the oscilloscope screen fills the picture. Adjust lighting and position to minimize reflections.

After you take the picture, transfer it to a PC. You can then use an image-editing program to crop, rotate, and otherwise enhance the photo as necessary. To add annotations, such as text and arrows, to the image, you can import the image into a drawing program, although some image-editing programs offer this capability as well. You can then print the final image, insert it in a document, or add it to a Web page.

For output to monochrome devices, such as a black-and-white printer, it can be advantageous to first convert the color image to monochrome and then reverse the result: Change the white to black and the black to white. This procedure results in sharp, dark lines for the oscilloscope traces against a light-gray background. Some digital cameras have a monochrome mode.

The image in Figure 1 illustrates the results of this procedure in capturing a timing measurement using a Sony Ma-vica MVC-FD7 camera set to monochrome mode. After image capture, the next step is cropping the resulting JPEG image using Microsoft Photo Editor 3.0 and then applying a reverse effect to swap the black and white tones. Finally, importing the image to Micrografx Windows Draw 6.0 allows you to add annotations, such as in the figure. (DI #2452)