The project is used for repairing of broken PC monitors. It can generate video signals with 8 different raster images. The tester features 4 resolutions for each image combination: 640x480x60Hz, 800x600x60Hz, 1024x768x60Hz, and 1280x1024x60Hz. Main component of the project is MCU AVR AtTiny2313 from Atmel running at 20MHz.
MCU generates horizontal and vertical sync signals directly from its ports. While resistor network work as simple D/A converter to convert R,G,B signals to analog signal (0~0.7V). This portable tester is powered by battery or DC power supply adapter operation: 7.5V~12V. If you are interested to build small Monitor Tester, here is the source code (ASM/HEX) and schematic (Eagle format).