This is a GPU made with Atlmel AT90S2313. It can be programmed using computer with a printer cable or a USBasp device.

With a 4Mhz oscillator and some resistors, it is possible to create a signal on its PB0 and PB1 pins. With a voltage divider and a resistor ladder, those signals can be converted to a composite video signal.

The encoding is done with two resistors: 1Kohm and 470Ohm, which is connected to a 1uF capacitor. The signal is as follows: 0.3V for black, 0.7Volt for gray and 1V for white.

Download Hex code from here (atmelbars.hex)

A typical video signal varies from 0V to 1V.

Like the chart above, I have the signal as follows: 11 for white, 01 for black, 10, for gray.

You can use any programmer (Khazama AVR programmer, ALTMEL command line programmer, AVRfreaks programmer etc), I personallly liked Khazama programmer for its simplicity. The program is simple, you want a set of binary number on any of the PB ports. I have used two resistors 1Kohm and 470 Ohm to stablize the voltage.