VGA mode used: 640x480 @ 31,5kHz/60Hz, (virtual) dot clock 25 MHz, visible information per line: ≈ 80%.
Bitmap size displayed: 128x120x4 (every pixel is a rectangle of 5x4 dot cells), using fixed DOS/Windows/CGA palette.
When you clone this, pay attention to copyright issues for your picture when you choose one yourself! However, this construction, firmware, and test pattern has BSD lisence.
The quartz crystal frequency is only 20 MHz (the ATmega88-20 is not overclocked). All components are available at Reichelt. The optimum microcontroller would be ATtiny84-20.
This PCB design (Eagle, SMD) for usual nine-pin SubD adapters uses a plug and a socket, so you have both genders readily available.
For power sourcing, 5 V are to be tapped using USB, a keyboard adapter, or a small wall wart, 30 mA, 150 mW. Much more power-saving than a running PC. Download of whole project or browse zipfile on server.
Freeware, open-source, you can use it for what your want, even commercially. Keep a copyright notice when you use this project with small or no modifications.
Based on „Monitor3.asm“, but with heavy code changes to reduce the necessary clock frequency. Moreover, the original Monitor3.asm has no exact timing that leads to put the monitor into stand-by(!) sometimes. This device / this firmware is error free! Moreover, it saves power as much as possible with interrupt-driven line output.