[deutsch]

VGA test pattern generator with ATmega88

This device is a simple and useful RGB signal generator for testing VGA monitors using ATmega88.

[Schematic]
Schematic: quite easy

Intended for feeding (TFT) monitors while repairing and burn-in, to keep them out of stand-by.

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.

[Picture]

Monitors expect 1 VSS voltage
RN2 = 470 Ω
like in schematic, seems to be non-perfect
RN2 = 680 Ω
not available at Reichelt, but at Bürklin

If your monitor clips input voltage to 0,7 VSS:
RN2 = 470 Ω
RN2 = 680 Ω

Visible picture at different values for RN2 (click radio buttons to switch!)

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.

[Population]
Population of this two-sided, 1 mm thick PCB

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.

[Photo]
Inner view

Download of whole project and 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.

[Foto] [Foto]
Here you see my test bench, and how it works

Based on „Monitor3.asm“, but with heavy code changes to reduce the necessary clock frequency. Moreover, the Monitor3.asm has no exact timing that leads to put the monitor into stand-by(!) sometimes.

haftmann#software, March 7, 2012