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 Hardware Dirt Cheap Frame Grabber V2.02  Michael Day 24.01.1992

It is a complex of hardware device and pascal program. The purpose of the DCFG is to simply provide a very simple method to grab video pictures and display them on a computer monitor.



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Dirt Cheap Frame Grabber V2.02 by Michael Day as of 5 January 1992 Public Domain This device is free and released to the public domain. If you actually find a use for it, all the more power to ya! The purpose of the DCFG is to simply provide a very simple method to grab video pictures and display them on a computer monitor. Version 1.01 of the DCFG only provided 4 levels of gray scale. Version 2.01 makes a modification which allows for 12 gray scales by reading the port four times and interpolating the results. Version 2.02 fixes a schematic error (DO3 is pin 5, not pin 4). The DCFG requires at least a 80286 or better and a VGA display to run. While it is possible to change the program to allow operation on a 8086 and/or a different display, I'm not doing it. If you want to, you can. My intent was to just prove that it was possible. The frame grabber program at this point is very simple, and as a result has some problems. The heart of the program relies on a very fast IO port to memory instruction. It can operate as fast as the computer can shove data from the port to the memory. This is as fast as DMAing the data could do. This method is sensitive to computer speed. As such, you may not get a stable picture at first. If you don't, use the left or right arrow keys to adjust the horizontal sample size. The up/down arrows adjust the vertical sample size, but this normally doesn't need to be done. You will probably notice some sparkles (pixels shifting left and right one pixel position). This is caused by sample jitter and is normal. All sampling systems have this problem. Some less than others. Even your TV has the problem, but it is normally good enough that you don't see it. The jitter is caused by the fact that the sampler is not perfectly synchronized to the incoming video signal. Your TV has a lot of circuitry in it to achieve the synchronization. Being that this is a dirt cheap frame grabber, there is only limited synchronization of the picture, and no synchronization of the sampler. If you want to try to improve on it, please do. To use the Dirt Cheap Frame Grabber, plug it into a PC printer port, and attach the other end to the video output from a VCR or TV Monitor and run the program. Use the left or right arrow keys to adjust the horizontal sample size to obtain a stable picture. Do not attach the Dirt Cheap Frame Grabber to the computer with a long printer cable. We are dealing with high speed signals here (up to 4MHz). It requires as short a connection to the computer as you can give it. I built my circuit inside the back shell of the connector that plugs into the printer port on the computer. --- Future considerations for someone to do if they wish to improve on the design would be to improve the synchronization to reduce the jitter problem. At this point I don't have any ideas on how to improve the problem. Another improvement that is possible to do would be to analyze the captured video frame to determine the proper values to use for capturing the data such as scan line length in pixels, vertical sync length, total scan lines, etc. A mechanism to increase the size of the displayed picture, and maintain the best resolution possible while doing so. Save an image to disk or a series of images to make a movie. Be able to print a captured image. Integrate the image with sound. And of course integrating this stuff into Windows would be nice. That's all folks!