I'm experimenting with decoding the composite video from a Famicom's PPU to RGB. It'll never be as perfect as the NESRGB mod, but if I make this into a mod, it'll be a lot simpler to install. It needs four wires to connect it to the board - two for power, one from the PPU's video output, and one for the master clock oscillator.
It works by breaking the video signal down to an equivalent of S-Video, using two filters. The chroma channel goes to a comparator to make it a digital (binary) frequency signal. The luma channel gets compared against four voltage thresholds on four comparators. The five signals are sent to an FPGA which decodes the chroma signal, using the master clock as a reference. That outputs one of 12 possible hues plus the absence of colour. Combined with the current luma value gives the combination of all possible colours, which are looked up in a table and sent to the RGB output.
Apologies for the PotatoCam.
The FPGA development board is a FleaFPGA Classic from fleasystems.com.
The monitor is an NEC Multisync II running at 15kHz line rate.
The games are Super Mario Brothers, Bomber Man II and Binaryland.
