Feedback ZX Spectrum version (ULAdigitizer)

[c0pperdragon]

This thread is intended for feedback on using my ULAdigitizer.

[wthorch42]

I successfully installed and tested the ULAdigitizer on a Sinclair ZX Spectrum 48K rubber-key with an Issue 2 board. Installation was a little fiddly, having to wire between pads on the ULAdigitizer and the ULA pins, but went smoothly. I spoke with c0pperdragon about that and, in conjunction with some other feedback he'd received, he's considering changing the board design to "castellated", where the board would fit over the pins of the ULA and then you'd just flow solder into the appropriate vias.

I had to tweak the clock trimmer pots on my spectrum to get the clock frequency dialed in correctly to match what's expected by the digitizer, but I think that was specific to my Spectrum, and shouldn't be the case for most. As I understand it, Issue 3 and later Spectrums don't even have the trimmers.

You'll need at least the ALPHA 63A firmware release for your RGBtoHDMI to get the correct Spectrum LumaCode profile.

You can see my installation here.

[spatuluk]

I've been trying to get it to work with my issue 2 Speccy, but it's causing it to enter what seems to be a reset loop.

Sometimes it gets far enough for the Sinclair Research message to be displayed before it resets again. Without the digitizer, it's fine, and my ZX-VGA-JOY produces a perfect output. The composite output is awful, so maybe it's related to that, somehow.

[c0pperdragon]

Could to provide a photo of the install. Maybe I spot something that is not right.

[spatuluk]

sure..

20240331_105046_1.mp4

The composite mod is unpopulated, and I'm just using it as a platform for the phono.

[c0pperdragon]

Why did you connect everything with these long wires? I would expect this to wrack havoc on the signal integrity. Using just the shortest connections possible is clearly the first thing to try. You see on my installation pictures how I intended the thing to look.
https://github.com/c0pperdragon/LumaCode/wiki/ULAdigitizer-(for-ZX-Spectrum)#installation

[spatuluk]

I did that initially, but the result was even worse. it still entered a boot loop, but never displayed a white screen. my soldering was not great, though.

I'll give it another try in the correct position.

[c0pperdragon]

One thing to check is, if the problem is with the ULAdigitizer or with the RGBtoHDMI and its configuration. Try to plug the lumacode signal directly into a TV with composite video input. You should see a stable black&white picture (with vertical stripes encoding the colors).

[c0pperdragon]

When the board renders the rest of the system instable, there may be something wrong with the board itself, as it is actually designed to only passively listen to the signals with high-impedance inputs to not disturb the host machine.
Maybe there is something wrong with the voltage regulator or the grounding of the level shifters. Use a multimeter to check the continuity from the ground pin of the ULA (pin 40) to each of the GND pins of the level shifters (pin 10 of both the TSSOP-20 ICs). Also check if these ICs get proper 3.3V on their power pin (pin 20).

[spatuluk]

Ground continuity seems fine, and I'm getting 3.25v on the power pins. I've re-soldered the digitiser under the ULA, but output is exactly the same. Output to a composite monitor was also the same, with the constant resets meaning it never gets far enough to produce a stable picture.

[c0pperdragon]

Your soldering looks very reasonable and I can see no obvious shorts anywhere. Maybe there are some tiny bridges still on the input pins of U2 o U3 that would mess up the system bus.
Could you test for continuity between any neighbouring pins of these ICs? And if this does not get you any hints and you happen to have an oscilloscope, try to probe all the ULA pins that go to the board to see if anything fishy is going on.

[c0pperdragon]

Looking at the picture, my soldering of U3 indeed looks a tiny bit suspicious. Maybe there is some bridgeing that conducts just enough to mess with your system, but not enough to fail in my test harness.

[spatuluk]

on U2, pins 4, 5, and 6 are bridged, and 9 and 10.
on U3, pins 12, 13, and 14 are bridged, and 9 and 10.

I'm not sure what to look for with the ULA, but I already checked the CLK, which is 3.5 something-hertz.

[c0pperdragon]

I am not sure about your measurement procedure, but this amount of bridgeing is basically impossible given that the picture looks not so bad. Maybe it is just the best to give all pins of U2 and U3 a short reflow with your soldering iron. Add no extra solder but use some flux if available.

[spatuluk]

i just went from pin to pin with the multimeter set to continuity. however, it only gave short beeps for the pins, rather than the constant beep of holding the probes together. it's not documented, so i have no idea what that's about.

anyway, i now have an issue 3 motherboard, with a simple AV mod, and i transferred the board to that. it worked fine first try! :)

I guess something on the issue 2 mobo is barely working, and the digitiser pushed it over the edge, somehow.

Thanks for all the help, and sorry for wasting your time with my dodgy speccy. If it's any consolation, the output of the ULAdigitizer is amazing!

[c0pperdragon]

Maybe it is just the additional power draw of the ULAdigitizer that rendered your issue 2 board unstable.
Anyway, I am glad that it works now for you at least in the other machine. Congratulations.

[L1GHTF0RC3]

Hi there,
I am having problems getting this to work with an OSSC.
Tried installing on 2 issue 2 boards and now its installed in an issue 3b, but get the same result.Whatever settings i use on the OSSC i cant get the picture correct.

ULAdigitizer connected to composite input on tv.

Connected to OSSC no lumacode.

lumacode on.

install.

Hopefully im just missing something here.I cant find anyone else that is using ULAdigitizer and OSSC so i cant copy their settings.
Any help would be appreciated,thanks.

[c0pperdragon]

It looks very much like the OSSC is not sampling the correct total number of pixels per line. I don't know exactly where this setting is found, but it should be set to 448.

This video shows how to change all relevant settings. It is for the C64, but für the Specturm it should be very similar.
https://www.youtube.com/watch?v=6ZZGEm12jUI&t=180s

[L1GHTF0RC3]

Thanks for the link, i had already seen that video, thats what made me buy the board.
The thing that wasted time for me was the fact that my TV will not seem to accept 384x240 in line5x mode, i had to change OSSC to 320x240 output.
Anyway after a lot of playing around with various settings i now have a great picture.
Thanks for your efforts in making this board, it produces a bright clean picture.