ZX80 Core - new ZX80 motherboards

[XorA]

Pm Sent!

[RWAP]

Get some listed on SellMyRetro - it has a wider appeal than just this forum

Is it worth offering them as a complete kit?

[PokeMon]

Of course I will do in a few days.
I want let the chance to fill the pre-oders first.

[fatbob_gb]

I am interested in one of these boards.

PM Sent.

[questarian]

PM'd... Definitely want one!

[retrolab]

I'm interested, too.

PM sent.

[PokeMon]

Thank you all. Just need a PM, no need to explicitly post here as I read my PMs daily.

[retrolab]

Hello PokeMon.

Do you have any pictures with the ZX80Core working to compare video quality? I have read the recommendation about buying the additional video module and I would like to compare the image with composite image, if it is possible.

Thank you very much.

[PokeMon]

First I show you the original schematic of the ZX80 to explain:

zx80modsch.gif (4.36 KiB) Viewed 4619 times

The signal is mixed through resistors R30 (1k) and R32 (330R) as VIDEO (pixel information) and SYNC.
This is okay for the ASTEC modulator, which has a impedance of about 1k.
You can imagine what the video signal level will do on a 75R impedance (like an video imput of a TV or similar, composite video).
It breaks down and the signal has much noise level.

So this will be the picture I found when connecting composite video input directly to the standard ZX80 video signal (or ZX80CORE) mixed over resistors:
The brightness has to be increased to nearly maximum to see anything due to the missing back porch (another problem).

zx80core_video-ovload1_s.jpg (129.5 KiB) Viewed 4619 times

So the next screen shows the video output with composite video using the module ZX8-CCB.
I choosed here a nice screen of a hanging ZX80 system as everybody knows the boring dump-my-name-screens.

zx80core_28C64_err2_s.jpg (274.25 KiB) Viewed 4619 times

The picture quality is much much better and improves the picture quality using the RF / UHF modulator for TV antenna as well.

[PokeMon]

I show you the video signals as well, here you can see the difference very good as well (for electronics engineers).
This is the original signal using 75R load.

zx80core_video-ovload2_s.jpg (159.59 KiB) Viewed 4619 times

And this is the signal looking with ZX8-CCB (using 75R load).

zx80core_video-backporch_s.jpg (100.22 KiB) Viewed 4619 times

You can see in comparison to the above the backporch, so you have a 3-level signal which shows a clear SYNC (lowest level), BLACK (middle level) and WHITE (highest level). And you can see the fine pixel going to low, I use the keyword PRINT to have a stronger signal you can better view.


So - up to you. I kept the video of ZX80CORE like the original ZX80 but left the option to improve it with a modern video driver like ZX8-CCB. You could do the simple transistor mod as well but you won't have a backporch with this simple impedance changer and have to rise up the brightness.