VGA to Composite ConverterVGA to Composite Converter
This circuit is designed from two sources I found, one at http://www.ccs.neu.edu/home/bchafy/lood.html and another that was included in the documentation for a vga to tv device driver here.
I used the first circuit to generate the greyscale video, and mixed in the composite sync obtained from the second circuit, I had tried just mixing in the Hsync and Vsync as per the first circuit but couldn't get this to sync the TV.
The adapter itself is no use without a driver on the computer to force the VGA adapter to use PAL/NTSC timings, the vgatv link explains the concept, but basically VGA is at a higher screen refresh than a tv signal, and needs to be slowed down to the right frequency. The driver above is out of date, but has the aforementioned circuit diagram in the help file. A newer version of the driver is available here there is also a windows driver available too. This driver works fine with my modified circuit, the video is only greyscale of course, for colour you'd need to build the complex circuit with ICs.
The Circuit Diagram:
The +ve PSU pin can be whatever voltage you have available, it definitely works with 5v and 12v, and I am currently using the adapter with a battery clip and 9v PP3 battery to avoid needing another PSU, if you were using the circuit on a PC all the time you could easily bring the 0 and 5v lines out from a spare plug on your computer power supply through one of the many dust collection holes PCs seem to have!