Grayscale Uzebox (no AD725)

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unebonnevie
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Grayscale Uzebox (no AD725)

Post by unebonnevie » Sat Oct 03, 2020 3:59 am

After a long time, I've decided to make a board for this, based on the R2R DAC from http://belogic.com/uzebox/schematics/uz ... mal_v2.pdf. I just sent the board the JLCPCB.

Here is a picture of my board from a Gerber viewer from JLCPCB. There is no AD725 chip, course. The board has:

1) USB power only, no DC connector, thus no 7805 regulator, because one can get a USB plug to have 5V of 1A minimum output.
2) I put in the CH340G, a very usable AND cheap USB-serial chip.
3) SD CARD has multiple connection support, include the original, micro-SD card, or simply headers.

I don't know if it works, but I will try it out when the board arrives.

Attached is the image.
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UZEBOX-GRAYSCALE.png
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D3thAdd3r
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Re: Grayscale Uzebox (no AD725)

Post by D3thAdd3r » Sat Oct 03, 2020 8:09 pm

This one should be interesting to see and I am curious what the grayscale looks like for games. So do you think the CH340G can be used for flashing, or did you envision some other PC<>Uzebox communications?

unebonnevie
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Re: Grayscale Uzebox (no AD725)

Post by unebonnevie » Sun Oct 04, 2020 7:22 am

Yes, the USB serial is there for flashing and communication. I figured if I have USB as the power, might as well throw in the CH430, which is dirt cheap compared to FTL232 USB-serial chip, and the CH430 works well.

dave
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Re: Grayscale Uzebox (no AD725)

Post by dave » Mon Nov 30, 2020 10:20 am

By the way, if you want a proper RGB->grayscale conversion, you might want to use the resistor network from the "Y" channel of the Y/Pb/Pr design I posted here. This network should also be more correct WRT the 75 ohm termination (the original black&white uzebox design uses 75 Ohm to ground in parallel with all the other DAC resistors, resulting in less than 75 ohm effective termination resistance).
  • Y - GND: 120
  • RED2 - Y 2k3
  • RED1 - Y: 4k3
  • RED0 - Y: 8k2
  • GREEN2 - Y: 604
  • GREEN1 - Y: 1k2
  • GREEN0 - Y: 2k4
  • BLUE1 - Y : 6k2
  • BLUE0 - Y : 13k
  • SYNC - Y : 604
This seems to work well here, see the attached screenshot, though I haven't installed the controller connectors yet, so only tested with a static image so far.
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D3thAdd3r
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Re: Grayscale Uzebox (no AD725)

Post by D3thAdd3r » Wed Dec 02, 2020 5:10 am

Hey nice work, it looks good :ugeek:

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uze6666
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Re: Grayscale Uzebox (no AD725)

Post by uze6666 » Sat Sep 25, 2021 2:26 am

Nice work! Have completed the whole build and it's working? If so can you send me your gerbers, schematic and BOM so I can add them to the downloads page of the website?

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