Atom Video to HDMI Adapter
Re: Atom Video to HDMI Adapter
How important is is that R2 and R4 are 1K1 1% and metal film?
Reichelt have sent me 7K5 in a bag marked up as 1K1.
I have some carbon film ones that I can put in series to get 1K1 until I reorder the proper ones.
Neil.
Reichelt have sent me 7K5 in a bag marked up as 1K1.
I have some carbon film ones that I can put in series to get 1K1 until I reorder the proper ones.
Neil.
Atom | BBC Model A | BBC Model B | Electron | Olivetti PC128S.
Re: Atom Video to HDMI Adapter
Or put 9 of the 7.5k in parallel
would miss the 1% tolerance though.

Re: Atom Video to HDMI Adapter
These are fairly critical components, being part of a voltage divider.
You'll probably be OK with 5% tolerance as a temporary measure.
Or you could, I think, try 1.2K and 8.2K, as that's almost the same ratio.
Dave
Re: Atom Video to HDMI Adapter
It gets worse!
They have also sent me 10Mohm instead of 10K.
I've complained to Reichelt and asked for the correct parts.
That'll take them a few working days to sort out but I don't have my programmer yet so I can potentially wait.
That's dulled my excitement somewhat.
Neil.
They have also sent me 10Mohm instead of 10K.
I've complained to Reichelt and asked for the correct parts.
That'll take them a few working days to sort out but I don't have my programmer yet so I can potentially wait.
That's dulled my excitement somewhat.
Neil.
Atom | BBC Model A | BBC Model B | Electron | Olivetti PC128S.
Re: Atom Video to HDMI Adapter
I am happy to send you three resistors of 4.7k
FPGAtom: much better than Atom2k15 which was even better than the real thing.
MAN WOMAN
MAN WOMAN

Re: Atom Video to HDMI Adapter
Its OK Roland, I'll wait until Reichelt sort out my order. Like I said before, I can't program the CPLD just yet anyway.
Here's the progress so far, just the HDMI hole to make, add 5 resistors, insert the comparators and get the right spacers for the Pi Zero to do....
Neil.
Atom | BBC Model A | BBC Model B | Electron | Olivetti PC128S.
Re: Atom Video to HDMI Adapter
Mine started up first time:
Unfortunately I don't have any Atom software accessible at the moment so I haven't been able to do any further testing.
I'll have to get the Econet setup properly as I don't have any other way of loading software.
I found an error in the BOM:
R6 and R7 are swapped, R6 should be 1K and R7 should be 430R
EDIT:
I typed in the test program in the wiki and successfully aligned the converter. Here's a screen capture from the Pi:
Unfortunately I don't have any Atom software accessible at the moment so I haven't been able to do any further testing.
I'll have to get the Econet setup properly as I don't have any other way of loading software.
I found an error in the BOM:
R6 and R7 are swapped, R6 should be 1K and R7 should be 430R
EDIT:
I typed in the test program in the wiki and successfully aligned the converter. Here's a screen capture from the Pi:
Last edited by IanB on Sat May 11, 2019 1:18 am, edited 2 times in total.
Re: Atom Video to HDMI Adapter
Good spot, that's corrected now.
I really must figure out how to get KiCad to generate the BOM. I just need to find the right plugin I think.
And great that a second person has one of these working!
Dave
Re: Atom Video to HDMI Adapter
IIRC it's in PCBnew: File -> Fabrication output -> BOM
FPGAtom: much better than Atom2k15 which was even better than the real thing.
MAN WOMAN
MAN WOMAN

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Re: Atom Video to HDMI Adapter
I may be mistaken, but I think you have the CPLD round the wrong way-B- wrote: ↑Fri May 10, 2019 10:13 pmIts OK Roland, I'll wait until Reichelt sort out my order. Like I said before, I can't program the CPLD just yet anyway.
Here's the progress so far, just the HDMI hole to make, add 5 resistors, insert the comparators and get the right spacers for the Pi Zero to do....
IMG_4425.jpeg
Neil.

The chamfered corner should be to the top right in your picture.
Chris
Re: Atom Video to HDMI Adapter
When I compare the pictures of Hoglet en -B- then it seems right to me:
FPGAtom: much better than Atom2k15 which was even better than the real thing.
MAN WOMAN
MAN WOMAN

Re: Atom Video to HDMI Adapter
You can see in Neil's picture here the location of pin 1 is marked with a circle (and a line extending out from the footprint): On the CPLD, the corner with pin 1 is marked with a small dot, and with a chamfered corner.sparkyhall wrote: ↑Sat May 11, 2019 7:35 amI may be mistaken, but I think you have the CPLD round the wrong way![]()
The chamfered corner should be to the top right in your picture.
So Neil has it the right way around (phew)!
Sparkyhall, what made you think that was incorrect? I want to make sure I've not written this down incorrectly somewhere.
Last edited by hoglet on Sat May 11, 2019 8:17 am, edited 1 time in total.
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Re: Atom Video to HDMI Adapter
My sincerest apologies, I had my board the wrong way round when I compared the two and I hadn't drunk my coffee before posting. 
Mines also built, I am also waiting for my programmer to arrive.
Chris

Mines also built, I am also waiting for my programmer to arrive.
Chris
Re: Atom Video to HDMI Adapter
Getting there, just a couple more resistors to fit when they arrive:
Hopefully not too many mistakes, if anyone can spot some then please comment
I only had 5% resistors so will measure values before powering up. The ones I've ordered are 1%
Andy
Hopefully not too many mistakes, if anyone can spot some then please comment

Andy
Re: Atom Video to HDMI Adapter
Important Note!!!
Everyone, do please check that you have R6 and R7 the correct way around: R6 is 1K0 and R7 is 430R.
IanB spotted that these were swapped in the BOM (which is now fixed). They always were correct on the schematic.
You can see them in this photo next to C4: R6 is the bottom one (1K0) and R7 is above that (430R)
They look incorrect in Neil and Andy's photos.
Dave
Everyone, do please check that you have R6 and R7 the correct way around: R6 is 1K0 and R7 is 430R.
IanB spotted that these were swapped in the BOM (which is now fixed). They always were correct on the schematic.
You can see them in this photo next to C4: R6 is the bottom one (1K0) and R7 is above that (430R)
They look incorrect in Neil and Andy's photos.
Dave
Re: Atom Video to HDMI Adapter
Thank you Dave I was assembling as per earlier BOM
Best
Andy
Best
Andy
Re: Atom Video to HDMI Adapter
All finished and cased up:
I had to cut quite a large hole for the HDMI connector to accomodate the plastic body of the connector as well as the metal part because the case walls were too thick to allow the connector to mate properly
I had to cut quite a large hole for the HDMI connector to accomodate the plastic body of the connector as well as the metal part because the case walls were too thick to allow the connector to mate properly
Last edited by IanB on Sun May 12, 2019 2:09 am, edited 1 time in total.
Re: Atom Video to HDMI Adapter
Yes, I had to do that as well.
On the plus side, it does give a bit of extra mechanical stability.
Dave
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Re: Atom Video to HDMI Adapter
Well, my programmer turned up yesterday so I was able to complete my Atom to HDMI adapter:
I'm really pleased with the results, my atom screen has never looked so good, and this on a 1366x768 display.
One minor error on the build instructions is that C18 is listed as an 0805 instead of through hole.
Need to spend some time playing with the options now.
Thanks to all those who made this possible.
Chris
I'm really pleased with the results, my atom screen has never looked so good, and this on a 1366x768 display.
One minor error on the build instructions is that C18 is listed as an 0805 instead of through hole.
Need to spend some time playing with the options now.
Thanks to all those who made this possible.
Chris
Re: Atom Video to HDMI Adapter
Hi Chris,
Glad you got it working.
Dave
Glad you got it working.
Fixed now, thanks.sparkyhall wrote: ↑Sun May 12, 2019 6:56 pmOne minor error on the build instructions is that C18 is listed as an 0805 instead of through hole.
The display looks slightly squashed to me, so you might want to experiment with different aspect ratio setting on the TV. You don't want it set to 4:3!
Dave
Re: Atom Video to HDMI Adapter
I just ordered the 0805 parts
Well, luckily they are not that expensive so that I have to cancel some projects

Well, luckily they are not that expensive so that I have to cancel some projects

FPGAtom: much better than Atom2k15 which was even better than the real thing.
MAN WOMAN
MAN WOMAN

Re: Atom Video to HDMI Adapter
Yes, it looks like it's squashing the Pi's 16:9 output to 4:3 so check the aspect ratio setting on the tv/monitor. The other possibility is that the Pi is generating the wrong resolution in Auto mode.
There is a potential problem with the current Atom CPLD profile as it's more or less setup for a 1600x1200 monitor although the following suggestions won't help with the 1366x768 resolution of sparkyhall's monitor which is going to be restricted to 3x3 integer scaling.
With sources that have border colour like the Atom in graphics mode, to get the best results, the capture area should be an integer sub-multiple of the display area so the border colour fills the whole screen. This also applies to the ZX81 which effectively has a white border colour due to the inverted video and also applies to the PC screen modes like CGA and EGA but not beeb, electron or monochrome sources as they can't set a border colour.
So if you are using a 1920x1080 monitor which has a centre 4:3 area of 1440x1080 the capture area should be 288x216 and for a 1600x1200 monitor the capture area should be 320x240 (with H and V offsets adjusted to centre the image). In both cases that results in integer scaling of 5x5 that fills the 4:3 screen area entirely thus preserving the border colour while maintaining integer scaling. I created two ZX81 profiles to work around this so maybe the same should be done for the AtomCPLD. However, a better solution would be to auto adjust the profile capture area to compensate for different monitor resolutions so I will investigate if that's feasible.
Here are a few comparisons in clear 4:
1600x1200 with 320x240 capture area
This scales 5x5 and fills the screen.
1920x1080 with current Atom_CPLD capture area (304x240)
This scales 4x4 with black left around the border area
You can always switch to interpolated full screen scaling to get rid of the extra black border but that will soften the image
1920x1080 with 288x216 capture area
This scales 5x5 and fills the screen but has a reduced border Note that the screen is not perfectly centred horizontally as the Atom CPLD doesn't have the delay setting to provide pixel accurate horizontal adjustment. There may not be enough room for a general delay setting but perhaps a fixed pixel offset of 1 or 2 pixels could be added to the CPLD?
Last edited by IanB on Mon May 13, 2019 3:27 am, edited 5 times in total.
Re: Atom Video to HDMI Adapter
When I chose 304x240 as a capture area, I didn't actually have a particular resolution in mind. What I was trying to replicate was the chunky green borders that you typically see on when an Atom drives a normal TV. And then, only approximately.IanB wrote: ↑Mon May 13, 2019 1:43 amThere is a potential problem with the current Atom CPLD profile as it's more or less setup for a 1600x1200 monitor although the following suggestions won't help with the 1366x768 resolution of sparkyhall's monitor which is going to be restricted to 3x3 integer scaling.
At 1280x720 it fills the screen vertically (with 3x scaling), similarly at 1600x1200 (with 5x scaling).
At other vertical resolutions, there will be some black borders.
I use this routinely at 1920x1080, where you get ~60 pixels above/below the image.
It's fine if people want to experiment with the geometry settings. We will get around to documenting these as some point. Honestly!
It's the "V Capture Height" that should be adjusted to eliminate the top/bottom border.
That would make a useful additional scaling option.
The Atom CPLD is pretty full, only one spare register.IanB wrote: ↑Mon May 13, 2019 1:43 amNote that the screen is not perfectly centred horizontally as the Atom CPLD doesn't have the delay setting to provide pixel accurate horizontal adjustment. There may not be enough room for a general delay setting but perhaps a fixed pixel offset of 1 or 2 pixels could be added to the CPLD?
Code: Select all
Function Mcells FB Inps Pterms IO
Block Used/Tot Used/Tot Used/Tot Used/Tot
FB1 18/18* 33/54 63/90 9/ 9*
FB2 18/18* 35/54 47/90 7/ 9
FB3 18/18* 32/54 76/90 9/ 9*
FB4 17/18 18/54 23/90 3/ 7
----- ----- ----- -----
71/72 118/216 209/360 28/34
Instead, I've just pushed a change that shifts the start of sampling over by one pixel. With this, the default profile is perfectly centered I think. There is an updated JEDEC file here:
https://github.com/hoglet67/RGBtoHDMI/b ... toHDMI.jed
Dave
Re: Atom Video to HDMI Adapter
I just tried this and it looks like the video is now centred in graphics modes, however I'm seeing glitches on the right hand edge of text mode:hoglet wrote: ↑Mon May 13, 2019 10:03 amInstead, I've just pushed a change that shifts the start of sampling over by one pixel. With this, the default profile is perfectly centered I think. There is an updated JEDEC file here:
https://github.com/hoglet67/RGBtoHDMI/b ... toHDMI.jed
They vary in the amount and colour, sometimes green and sometimes yellow. They appear to be at the end of the active text area, not at the end of sampling.
Re: Atom Video to HDMI Adapter
Do they go away if you recalibrate? (Using a text screen)
I'm busy this afternoon, but I'll look into this later.
I have a hunch I know what's going on, it's to do with the way the colour difference signals are sub-sampled. Adding a 1 pixel offset will shift the optimal colour sampling point into the 8-15 region.
Dave
Last edited by hoglet on Mon May 13, 2019 1:11 pm, edited 4 times in total.
Re: Atom Video to HDMI Adapter
Yes, the optimum value has changed from 1 to 9
During calibration similar glitches are seen at the left hand side as well
Re: Atom Video to HDMI Adapter
I've just pushed another Atom CPLD version (v2.4) that adjusts the colour sampling point so the optimal value is back in the 0-7 range. This means the previous profile should work unchanged. So please give that a try.
Some background... It's possible (and beneficial) to sub-sample the chrominance signals by a factor of two. That's because the highest resolution colour mode (128x192) is half the resolution of the the highest resolution monochrome (256x192). I'm currently taking the chrominance sample exactly half way between the two luminance samples, as some earlier tests suggested this worked well. There is possibly scope for further optimising this, but unless anyone reports issues I'm not going to try.
Dave
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Re: Atom Video to HDMI Adapter
You're spot on, TV was set to 4:3, now I have set it to 16:9 it looks much better.hoglet wrote: ↑Sun May 12, 2019 7:51 pmHi Chris,
Glad you got it working.Fixed now, thanks.sparkyhall wrote: ↑Sun May 12, 2019 6:56 pmOne minor error on the build instructions is that C18 is listed as an 0805 instead of through hole.The display looks slightly squashed to me, so you might want to experiment with different aspect ratio setting on the TV. You don't want it set to 4:3!
Dave
Chris