From the images and demo videos, it is obvious that the video quality is barely acceptable. There are two main problems:
- image sharpness - there is cross-bleeding of colors, noise artifacts etc.
- color resolution - only 8 basic colors are supported
Solutions for image sharpness
The flash A/D as I prototyped is very much a "chewing gum/duct-tape" solution, that can be improved in many ways:
- Put the circuit on a permanent solder board
- Keep wiring trimmed and matched
- Use higher quality potentiometers that allow finer and more stable regulation of threshold voltage
- Introduce external 21.47727MHz crystal to drive the sampler circuit instead of multiplying CPUCLK (which is XTAL/6) by 6 on FPGA
Solutions for color resolution
With 1-bit flash A/D per color channel only following colors can be supported:
For a small improvement of resolution, for example from 1 to 2 bits, additional LM339 comparator per color channel could be used. However using 6 LM339s instead of 3 would not double the color resolution. Reason is that 2 LM339 set at 1/3 and 2/3 thresholds would produce 3 valid combinations:
|01||color intensity low|
|10||(ignore, as should not occur: if the higher LM339 is over the threshold, lower must be too)|
|11||color intensity high|
Still, 6-bit color digital vector obtained like this could be simply mapped at least to a valid 16-color table.
One additional interesting experiment would be to use the popular LM3914 dot-bar driver chip as a flash A/D. Theoretically, full 3-bit A/D conversion could be obtained from its 10 stage outputs.