Hi there guys,
A while back people were talking about using the LM1881N chip to do the sync signal separation needed to get game console video output to work correctly in an arcade machine.
I commented (to what avail I'm not sure) that this was not enough in most cases as the video output of a game console is often AC-coupled. (The baseline of the RGB signal is not 0v)
So you will get proper sync, but you will not get proper RGB levels and it can (will) look tinted/washed out.
An example of this is the Playstation 2, where it will "work" but you will get a tinted image with nasty color saturation issues.
This can be "compensated" for by cranking up and playing with the RGB pots on the monitor chassis, however this is not a real solution to the problem, and often times the remote board pots are not even enough... and you have to adjust the gain pots on the chassis itself to get decent looking levels.
The downside to this is that it doesn't really "fix" the problem and it also means when you put anything else into the cab your color levels will be really messed up.
To solve the problem, I've designed a PCB that does both the sync separation and "DC restoration" on all 3 color channels.
It has a 6 pin input header which takes Red, Green, Blue, Composite Video, Ground, and +5v. (All can be sourced from a SCART connector)
The output is another 6 pin header which outputs Red, Green, Blue, Ground, CSync, and VSync.
The color signals are all "restored" to a 0v baseline so they will be in the exact signal format that the arcade CRT expects.
It performs this level calibration automatically, so you do not need to turn any pots to achieve the correct levels. The whole process is adaptive and automatic based on the input signals.
Below is a picture of the PCB layout:
I have commissioned the production of two prototype PCBs this week, which should arrive by the end of next week. (Or soon thereafter)
Assuming everything works as expected (the same way my early prototypes here do) I will be offering them to the community at a very low price... it depends on how many people are interested, but it'll be between $30 and $50 a board. ($30 if we can get > 20 orders, $40-$50 if we only end up with a couple)
The boards are all commercial quality finished, with soldermask, silkscreen labeling, etc. (I have contracted a PCB fab plant in asia to do the board production)
I have selected the highest quality components possible for the board, including 1% tolerance for all resistor components for the best possible signal quality and minimal to no interference. (This is about as good as it gets)
I am also investigating a version that will do the same function from component video sources... but this is much more complex as it requires YCbCr colorspace conversion to RGB as well. (Which needs another chip that is much harder to integrate)
Also, the board is solderless using the following connectors for input/output:
Let me know if you are interested!
Hint: The trace that runs between Pins 1 & 2 of Amp B is dangerously close to either pin. I'm assuming those are SO-8 packages on the amps and running traces between SO-8 pins any larger than 10mils is not wise because depending on the board mfg. you use, they may or may not be high quality boards and in the event that they aren't, you may actually have whiskers connecting pads/traces that are too close together.