Instead of using a scaler such as the XRGB or modified GBS series, you can add scanlines to an RGB Scart signal. It’s not as neat as using a scaler, nor does it provide as good an experience, but I wanted to make one just out of curiosity, especially after seeing one for sale at ArcadeForge.
I use a piece of matrix board, cut 8 x 16 holes, it’s very similar to the board I used when creating an add-on for the GBS scaler, it’s really just the most basic scanline circuit combined with an LM1881 sync stripper (check those guides for information on parts needed). The LM1881 has a Composite Sync and Vertical Sync output on it, we are going to use these as Horizontal and Vertical Sync inputs into the Scanline circuit.
Making the board is very similar to the GBS Add-on guide, so please check that out as well as the photos and info below.
Ideally, I wanted it to not use a project box and instead have something which meant I wouldn’t have to cut too many holes for the scart socket, cables etc. Then I found this on ebay – a scart pass-thru adapter with A/V phono breakout cables.
Easy to take apart, just four clips to open, then pop it open.
This looks perfect, I unsoldered the phono wires from the rear of the scart socket, leaving me with just a scart pass through adapter.
I test fitted my piece of Matrix board – cut down to 16 x 8 holes.
I don’t want to repeat the majority of the GBS Add-on guide, so be sure to check that guide out to see how I link up the necessary legs of the chips and look at the photos below and diagrams above.
The Blue and Yellow wires forming a cross in the photo below are the Sync outputs of the LM1881 chip going to the Sync inputs of the 74LS74 chip.
The Scart pass through housing already had a hole in the side that previously had the phono leads passing through it, nice and easy to re-purpose for the on/off/on switch. This is a 3 position switch, centre off, which will allow us to select odd scanlines, no scanlines, even scanlines.
I had to make a small hole for the screw to hold the switch in place, and fold one end of the switch mount over so that it will fit in the space for it. (sorry, it’s not very clear from the photos below)
Fits okay :-)
Added the required wires to the board now, yellow is the Sync/Composite video input for the LM1881. The thicker red and black wires are for 5v and GND, the thin Red, Green and Blue wires are for the scanlines (doesn’t really matter which is which to be honest).
A pretty good fit. If you look closely you’ll see I next soldered on the wires for the switch, colour coded as per the diagram above, the wires are soldered directly to the chip legs on the upper side of the board.
I decided to solder the Sync and 5v wires first, these are Scart pins 20 and 8, so both along the same row of pins.
Then I put the rest of the scart plug/socket in place and then solder the RGB wires and GND. I just realised I forgot to explain that I had previously linked up all the GND contacts on the back of the scart socket with some small pieces of thin wire.
Pop it back together and you’ve got a very tidy little unit.
Here’s Outrun running on my Saturn, the ghosting affect you can see on the clouds is just because it was scrolling fast and I snapped the photo at just the wrong time.
This looks a lot better when you’re sat away from the TV. It’s not as good as a dedicated scaler with a scanline generator, but it is an interesting and cheap alternative.
Don’t forget, if you prefer – you can purchase a professional unit from ArcadeForge!