exxos's Atari, Amiga & retro forum

I have some questions about the RGBtoHDMI project (hardware which adds HDMI video output to a range of vintage computers). I intend to add it to an STe:

1) According to the official Wiki project page for RGBtoHDMI 12-bit board, it is now at version 4. But several sellers have a version 7 (CJEmicros and RetroHackShack to mention a couple).

Is this an unoffical offshoot from the official one?
Is there a website with more information?
Are there file-downloads somewhere so I can make my own?

2) As I don't have much experience with SMD components and there's so much that can go wrong with this project (also involving multiple boards) I would like to buy it (and the other boards needed for it) ready-made.
I see that several PCB-manufacturing companies also offer ready made boards and not just bare boards, one of them being PCBway.
I suppose it's also possible to upload the Gerber and BOM files to other manufacturers.
Has anyone here ordered ready made RGBtoHDMI and 12-bit Extender boards? How did they come out and how much did they cost?

3) Since there's no buffer board available for the STe I'm working on a design for that, but I'm confused about the signal pins of the RGBtoHDMI and 12-bit extender boards. I've compared several of the existing buffer boards (Atari ST, Amiga, Atari ST with no buffer etc.) and I see that the signals aren't the same.
For instance, in one design (12-bit Atari ST buffered pickup board) the R3, G3 and B3 pins all receive the Atari ST MONO signal.
In other designs the SYNC pin receives a variety of sync type signals, and a modified Amiga buffer for use with the STe has CSYNC going to the SYNC pin of the RGBtoHDMI and MONO going to the VSYNC pin.
Is this because although the RGBtoHDMI input pins have a specific signal labelling they're not fixed, but the actual signal it will carry is determined by which profile has been chosen, differing between the various vintage computer settings?

The answer to question 3 will be that ST only had a 9-bit colour and STe had 12-bit colour and so on the ST there is no R3, G3 or B3

alexh wrote: 18 Sep 2026 20:12 The answer to question 3 will be that ST only had a 9-bit colour and STe had 12-bit colour and so on the ST there is no R3, G3 or B3

Thanks for confirming :thumbup:

Would it then be safe to also assume that the reason for the different signal names (on the input pins of the RGBtoHDMI) are indeed because they're not hardwired and fixed, but re-configurable. So the signal names don't necessarily match the actual signal received. Do you agree?
For instance, comparing the STe and ST, here showing only the pins that differ for simplicity (and with pin numbers of the RGBtoHDMI input connector in paranthesis):

ST	STe	RGBtoHDMI input connector
MONO	R3	R3 (11)
MONO	G3	G3 (13)
MONO	B3	B3 (15)
HSYNC	CSYNC	SYNC (12)
VSYNC	MONO	VSYNC (14)

These topics over on AF are probably helpful to you:

Flow diagrams which help understanding of how it works with ST & STe:
https://www.atari-forum.com/viewtopic.p ... 98#p487598

MegaSTe wiring:
https://www.atari-forum.com/viewtopic.p ... 08#p488108

STe wiring:
From page 4: https://www.atari-forum.com/viewtopic.p ... 21#p420221

Some slight differences in wiring, perhaps there was an error on page 4.
From page 5: https://www.atari-forum.com/viewtopic.p ... 17#p421117

I have 5 ready built rgb2hdmi hats if you want one, PM me. They are 12 bit issue 4's.

They have had basic tests done, they boot, displays the menu etc and the CPLD was programmable via RPi.

I haven't fully tested yet but I can if you want one.