All Digital NTSC Color
July 13, 2014
Generate NTSC color signal using only digital integrated circuits. An 8-bit microcontroller (Atmega16) and a shift register (74LS195) are used to produce NTSC color signal compatible with modern flat screen TVs. The schematic and source code are here.
What colors can it produce?
Below is a sample palette produced by this technique.
How to use
Build the circuit in the schematic below and program the microcontroller with the binary file in the repository. Hook it up to a TV, and you should see a color palette.
How does it work?
NTSC color works by superposing a 3.579545 MHz sub-carrier wave on top of the Black and White NTSC signal. The phase of the subcarrier indicates the color of the "pixel".
A 14.31818 MHz clock, which is 4 times the sub-carrier frequency, is passed through a shift register to generate 4 phases the sub-carrier. The amplitude of these phases in the output signal is controlled by the microcontroller. Thus, different amounts of the in-phase and quadrature components can be added to obtain different colors.
This series of blog posts describes NTSC signals in more detail.