Futhermore, few extra non-arcade related goals were set:

What is such a card good for? Can we simply use TV output from our standard PC video card? Or can we use HDMI to CVBS (TV) convertor? These questions are frequently asked. The answer depends whether you are happy with the output of the avaialble solutions. Many arcade fans are not because of several reasons, but the main one is the refresh rate of the TV output signal produced by the standard video cards, which is locked to either 50 or 60Hz. There is plenty of arcade games that use frame rates different than the standard rates. When such a game is displayed on a TV screen and especially if the game uses scrolling the animation of the scrolling judders and it spoils the game. Some people don't mind, some do. For those who want the best results without having an arcade cabinet in their living room Arvid may be the final solution as it doesn't need arcade monitor yet delivers perfect picture on standard European TV equipped with SCART connector. Note, the TV has to support RGB inputs which was quite common feature for the last 10 years or so these TV sets were produced.

A video of Arvid video card prototype running the port of arvidmame emulator is here.

Beaglebone (Black or Green) was selected as the base hardware for several reasons:

An extra circuit with the DACs has to be build according the schematics listed bellow. The circuit is now in matured state and meets the goals I set for the project.

The circuit is fairly simple and can be build without soldering just on a breadboard. The scart connector is connected to the breadboard either with soldered wires or via test hooks.

Beaglebone and a PC running an emulator is connected through an ethernet cable. I prefer to use network crossover cable to minimize data transfer latencies (no switch or hub is involved). The Beanglebone runs a network server application that receives compressed screens from the emulator, then sends them to GPIO pins to produce TV signal. On the PC side the emulator has to suport Arvid by calling functions defined in arvid client library. The arvid library is simple and straightforward and emulator authors should have no trouble adapt their programs to use it. Arvid firmware (video mode drivers) and software (network server, arvidmame emulator) are ready, see download section for more info.

if you use pcb, then you'll need few extras:

You can get most of the resistors in one bundled pack on eBay (look for '300PCS 30 Values 1/4W 1% Metal Film Resistors' for couple of dollars). The 1k05 resistors will have to be ordered separately though. Or alternatively you can connect 1k + 47 ohm resistors in series to get the desired value (the 47 ohm resistors should be in the bundle pack).

The 4066 quad bilateral switch IC doesn't do anything related to video signal generation, but it fixes Beaglebone start-up issue by disconnecting pins 41,43 and 44 from the ground. It's a shame this Beaglebone quirk has not been fixed yet (it exists even on BBG) otherwise the circuit could be made just out of resistors. The pins are connected when the sync signal is on. If you plan to build the circuit on a breadboard use a chip in DIP package (DIP-14) such as 74HC4066N (the cost is about $1 on eBay)

The Tate and Coin switches are optional, they make sense only if you plan to build-in Arvid into a cab or game console. Emulators and emulator frontends can use the TATE switch to set initial rotation of graphics on the screen. The coin button can be used (suprisingly) as a coin button to supplement missing 'Select' button on some older joysticks (like Sega Genesis Arcade joystick).

Before you connect the circuit to BBB(G) doublecheck every wire and its connections. Also before you first connect the SCART to your TV set doublecheck the output voltage (using multimeter) while Arvid service screen is on. The voltage on the output lines should never be bigger than 1.5 volts on the RGB wires and the sync line. The RGB switch signal however should measure 3.3V on circuit that is not plugged to the TV set.

If you've never build things like this before, just don't rush it. Take your time and tripple check every connection. The construction time is roughly around 4 hours (beginners), BBB setup can take another hour or two (again depending on experience).