A board for mixing VGA signals with sound and all kind of other signals. A build in Arduino generates a VGA signal, too. Each colour has its own chanel, Red Green, Blue.
For the Arduino one could use the code of that project: https://www.gammon.com.au/forum/?id=11608.

HSYNC and VSYNC signals are squared pulses of +5V, and the RGB signals take values in a continuous analog voltage range from +0V (absolutely dark) to +0.7V (maximum brightness).

vga-signal-generator_10.zip

H-Sync – 68 Ohm – Pin 03
V-Sync – 68 Ohm – Pin 10
R – 470 Ohm – Pin 04
G – 470 Ohm – Pin 05
B – 470 Ohm – Pin 06

VGA Video Signal Format
Arduino Uno output to VGA monitor
VGAX Library for Arduino UNO
VGA Signal Timing
Homemade VGA Adapter

The VGA Signal Generator was designed by Wolfgang Spahn 2017.
It is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.