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!