The 2068 Video Digitizer

A single board plugged into the 2068 expansion port can digitize and store any standard video image. Additionally the stored image can be changed in many ways, then saved to tape or disc, printed out on your printer or just viewed on the screen.

The original circuit drawing and design notes appeared in SINC-LINC January/February 1987 and March/April 1987. The Toronto Timex-Sinclair Users Club case up with a digitizer circuit consisting of eleven integrated circuits and one transistor. I sent for a board and the software included in January 1988. When I received the package in the mail just 6 days later I started a new project that is still on going. James G. Depuy of SMUG wrote a two page documentation on building and aligning the circuit board. I easily obtained the electronic parts needed to assemble the board at a local parts supply in Denver. Three of the IC’s are linear and the rest are low power Schottky digital types.

The software when loaded and running has a menu that allows the user to adjust the board for initial video sync and threshold settings. A visible scan of the video input is observed on the TS2068 monitor. If a video camera is used, the lens iris and other adjustments of the video signal can be made to optimize the image as it is being scanned. Digitizing is made from one to as many as eight scans that are stared in memory. Each scan is set by the computer to capture a different gray scale of the image. When viewed after completing all scans a digitized image can be reversed, inverted vertically and horizontally. A section of the screen can be cropped, moved and added to another screen by a cut and paste operation.

In order to get the eight scans to properly sample and merge progressively darker video image intensities, I had to add an inverter IC with reversed stair-stepped reference resistor array. As the software is written the gray scale starts out with the darkest image level and adds each lighter image. This is like cutting out a picture and painting it black and then trying to add detail with a black marker. The hardware modification was easier then trying to debug the program.

Last April John McMicheal offered a new program to drive the digitizer called VIDEOTEX, which corrected this gray scale problem and also reduced the number of gray levels displayed to four, but redefined the dot pattern to eliminate the “fabric” like texture evident in the original software.

Two other programs written by John are called VIDEO 3D and VIDEOCOPY. When these programs are used additional graphic functions are available, which will take a faster video file and produce an image that will show “depth” to the image and add color. The color can be added by VIDEOCOPY, which will colorize the gray scale image and print it to an OKIMATE 20 printer using an IBM parallel Plug ‘n Print cart.

I will have more information and start a review of the digitizer and the available software in the next newsletter issue.