You should read the NES Zapper Video Synth Theremin project log before this one because this project is a direct continuation of that and there are several concepts I'm not going to cover twice.

This is the VGA signal generator used in the last project. My design goal was to keep complexity and part count down. It didn't have to be perfect ,it just had to work. There were three main problems:

• The timing was based on an resistor-capacitor oscillator, and those are notoriously unstable.
• The resolution was 640x480 which I discovered isn't supported by some newer monitors
• The RGB signal is only porched during the Sync pulses which is way outside the VGA spec.

Here's a couple examples of bugs in the old VGA circuit:

The edge of the display is jagged because of instability in the RC oscillator.

Here the oscillator gets so unstable the image tears right off the screen.

These glitches are beautiful, but I have ambitions of taking the current project to performing arts venues and connecting to their projector systems. If a projector is picky about VGA signal quality it will turn the glitches into an ugly "bad signal" blue screen. This is why I've designed a new VGA signal generator following the opposite design philosophy. This time the IBM 8514 VGA standard is being followed religiously; no more "whatever works is good enough".