$25 24bit VGA GPIO hat for Raspb Pi! (most others are 18bit)

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kitty666cats
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$25 24bit VGA GPIO hat for Raspb Pi! (most others are 18bit)

Post by kitty666cats »

https://texelec.com/product/lo-tech-rpi-vga-board/

Anyone picked one of these up yet? Pretty cool-looking. With the exception of the ~$100+ RetroTink Ultimate (also 24bit), all other GPIO hats people use for emulation are 18bit. I personally just use a non-scaling HDMI to VGA DAC nowadays (or HDMI to YPbPr for consumer CRTs), but I've previously owned a VGA666 and RGB-Pi and the improvement in image quality from 18 to 24 was definitely very noticeable after getting so acclimated to the former!

Would have been very cool if it had a dip for RGBS instead of RGBHV like the RT Ultimate, but that's hardly an issue. I definitely plan on grabbing one soon, would love to hear thoughts if anyone here has one!
viletim
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Re: $25 24bit VGA GPIO hat for Raspb Pi! (most others are 18

Post by viletim »

This hardware has resistor DAC like the other cheap ones do. To get 8 bits per channel it would need to have a real video DAC on the board. For console games from the 16-bit era and earlier that have fixed palettes, there aren't enough colours on screen at any one time to notice any error, so it doesn't matter. It would certainly be noticeable on more modern games which were made to run on 24 bit RGB graphics hardware though.
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kitty666cats
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Re: $25 24bit VGA GPIO hat for Raspb Pi! (most others are 18

Post by kitty666cats »

viletim wrote:This hardware has resistor DAC like the other cheap ones do. To get 8 bits per channel it would need to have a real video DAC on the board. For console games from the 16-bit era and earlier that have fixed palettes, there aren't enough colours on screen at any one time to notice any error, so it doesn't matter. It would certainly be noticeable on more modern games which were made to run on 24 bit RGB graphics hardware though.
Do you know if those cheap reliable HDMI to VGA DACs have the same 'resistor DAC' you speak of? The non-scaling Portta is the one I have, and then there's that HDMI to YPbPr in the black box with kinda rounded top, the one Mike Chi suggests. Or are those what you were referring to...? Wasn't sure if you meant those, or the old VGA666 hats.
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xeos
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Re: $25 24bit VGA GPIO hat for Raspb Pi! (most others are 18

Post by xeos »

viletim wrote:This hardware has resistor DAC like the other cheap ones do. To get 8 bits per channel it would need to have a real video DAC on the board. For console games from the 16-bit era and earlier that have fixed palettes, there aren't enough colours on screen at any one time to notice any error, so it doesn't matter. It would certainly be noticeable on more modern games which were made to run on 24 bit RGB graphics hardware though.
is that a theory of something you've seen in practice? I'd think the number of colors wouldn't matter, since it's not using a palette/lookup table on the output side. it's just a question of whether the color errors are noticeable. With photos it might be moreso than for illustrated / drawn images.
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kitty666cats
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Re: $25 24bit VGA GPIO hat for Raspb Pi! (most others are 18

Post by kitty666cats »

viletim wrote:This hardware has resistor DAC like the other cheap ones do. To get 8 bits per channel it would need to have a real video DAC on the board. For console games from the 16-bit era and earlier that have fixed palettes, there aren't enough colours on screen at any one time to notice any error, so it doesn't matter. It would certainly be noticeable on more modern games which were made to run on 24 bit RGB graphics hardware though.

“ The Raspberry Pi uses HDMI for it’s built-in display interface, and it’s well documented that a second screen can be connected to the GPIO header when switched to ‘display parallel interface’ (DPI) mode. The DPI is powered from the Raspberry Pi’s GPU and so has the same performance and capabilities as the HDMI port – 1080p, 24-bit colour, 60Hz.

Project boards exist already to connect a VGA screen to the GPIO, but these are very simple designs and have some limitations such as 6-bit colour and sensitivity to interference from the wireless peripherals in the RPi 3. The RPi GPIO is also stressed by the TTL control signals in the VGA interface and the project boards lack the certifications needed to be offered as finished products.

The Lo-tech Raspberry Pi VGA Board aims to address these problems, providing a true-colour VGA Adapter in a ‘HAT’ PCB format that will provide a reliable VGA output for primary or secondary display purposes whilst protecting the RPi, both from ESD when the screen is connected hot and from over-stressing the GPIO outputs via buffering of the key control signals.

I’m excited to report that this board has just cleared EMC testing, meeting EN 55032:2015 Class B limits, and ESD testing, passing BS EN 61000-4-2:2009 level 4, and so can be pre-ordered today (first deliveries expected approx. February 2017).”

Here’s more deets on theirs!
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kitty666cats
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Re: $25 24bit VGA GPIO hat for Raspb Pi! (most others are 18

Post by kitty666cats »

Bumpin' to see if anyone has nabbed one of these. Probably should save my $ since I am good with HDMI to VGA already, heh
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xeos
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Re: $25 24bit VGA GPIO hat for Raspb Pi! (most others are 18

Post by xeos »

kitty666cats wrote:Bumpin' to see if anyone has nabbed one of these. Probably should save my $ since I am good with HDMI to VGA already, heh
yeah I'm curious what this really offers over a $2 hdmi ->vga adapter? Said adapter adds no more than 1ms of lag (I've measured it directly) and supports 120hz at lower resolutions (perhaps more), and 1920x1080 at 60hz....
setiawan
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Re: $25 24bit VGA GPIO hat for Raspb Pi! (most others are 18

Post by setiawan »

Just found out about this product. Has anyone gotten their hands on it and done a comparison? Does it really provide 24bit colour?

I don't really understand the technical reasons behind why basically every other hat only provides 18bit colour, but I've been assuming that it was some constraint of the Pi itself. Is this not the case?

Edit: Came across this interaction on the rpi forums, between Gert ("Gert van Loo", I think the original designer of the VGA666 board?) and the designer of the Lo-Tech 24bit board ("james-at-lo-tech"): https://www.raspberrypi.org/forums/view ... 5#p1079395

Still not sure what to make of what they're saying really. Something about the precision of resistors may possibly cause banding, the number of resistors required, and the VGA impedance of monitors being 75ohms..
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Guspaz
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Re: $25 24bit VGA GPIO hat for Raspb Pi! (most others are 18

Post by Guspaz »

He's saying that he designed his product to use cheap 1% resistors (resistors whose values can vary by up to 1% from their rated value), and so adding more bits of precision doesn't help with such imprecise resistors. In order to take advantage of more bits of precision, you'd need more expensive resistors.
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Re: $25 24bit VGA GPIO hat for Raspb Pi! (most others are 18

Post by setiawan »

Guspaz wrote:He's saying that he designed his product to use cheap 1% resistors (resistors whose values can vary by up to 1% from their rated value), and so adding more bits of precision doesn't help with such imprecise resistors. In order to take advantage of more bits of precision, you'd need more expensive resistors.
Ah I see. Lo-tech has put up a small wiki page about their product, where they list the models for the different resistors they use on the board: https://www.lo-tech.co.uk/wiki/Lo-tech_RPi_VGA_Adapter

I've looked them up and they're all rated to have a tolerance of 1%. Does this mean that it only 'might' produce 24bit colour, but unreliably so? Maybe even just as bad as 18bit?
mikechi2
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Re: $25 24bit VGA GPIO hat for Raspb Pi! (most others are 18

Post by mikechi2 »

It doesn't make sense to spend so much effort on these resistor strings when a proper video DAC, with real 75 ohm source termination, is readily accessible using the same connections.
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Re: $25 24bit VGA GPIO hat for Raspb Pi! (most others are 18

Post by kitty666cats »

I have not bothered picking this thing up.

If anything, I’m more curious about THIS instead -

https://www.tindie.com/products/takeit/ ... erry-pi-b/

Although at this point, I feel like any more $ put towards my Pi 3B+ would be better utilized on a dedicated emulation PC / Pi 4 / MiSTER!

That being said, I am always happy to see different GPIO hats for analog video.
https://www.ebay.com/itm/174326888301
https://www.ebay.com/itm/294027086102
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kitty666cats
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Re: $25 24bit VGA GPIO hat for Raspb Pi! (most others are 18

Post by kitty666cats »

BTW, I picked this up and it looks phenomenal - can use the same config.txt settings the RTUltimate implements in custom 15kHz etc Pi images. I use it with a sync combining circuit on my IIgs monitor:

https://www.instagram.com/p/CWIA7Zag-Gn/

https://www.instagram.com/p/CVoIzAxlO8h/

https://www.instagram.com/p/CUf2wG-FLRd/

https://www.instagram.com/p/CUf-HL_lhV5/

https://www.instagram.com/p/CUp7WC9FJr-/

https://www.instagram.com/p/CUJvR8ZAdrR/

Say what thou wilt about a resistor ladder being lazy design, but the thing works and looks great!
nes.og
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Re: $25 24bit VGA GPIO hat for Raspb Pi! (most others are 18

Post by nes.og »

I’m skeptical that a hat using a resistor ladder can display 24 bit color as accurately as a DAC. Would be interested to see some screen shots compared to a RT Ultimate.
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xeos
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Re: $25 24bit VGA GPIO hat for Raspb Pi! (most others are 18

Post by xeos »

nes.og wrote:I’m skeptical that a hat using a resistor ladder can display 24 bit color as accurately as a DAC. Would be interested to see some screen shots compared to a RT Ultimate.
why? I agree screen shots are always nice, but it's pretty damn hard to capture screens successfully so unless the quality was pretty gross I think it would be hard to tell the difference.
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Re: $25 24bit VGA GPIO hat for Raspb Pi! (most others are 18

Post by nes.og »

xeos wrote:
nes.og wrote:I’m skeptical that a hat using a resistor ladder can display 24 bit color as accurately as a DAC. Would be interested to see some screen shots compared to a RT Ultimate.
why? I agree screen shots are always nice, but it's pretty damn hard to capture screens successfully so unless the quality was pretty gross I think it would be hard to tell the difference.
Don’t think it would be would be very difficult. I’ll try to purchase one soon to post some comparison pics vs VGA666 and RT Ultimate.
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Re: $25 24bit VGA GPIO hat for Raspb Pi! (most others are 18

Post by kitty666cats »

I'm certain the RT Ultimate will yield a better image - RT Ultimate also doesn't require an obtuse setup with a sync combiner / outputs YPbPr and S-Video... it is obviously the superior unit! That being said, this thing is quite the hidden gem - it's substantially better-looking than the RGB-Pi and VGA666 I have owned in the past. Obvious kudos to Portta DACs / technically... Lontium. Those still reign supreme compared to any GPIO hat if you know what you are doing. @mikechi2 in particular knows the wonders of Lontium's DAC ICs! :)

Mike, if you see this - I am going to reach out to you with a question soon (not related to Pi GPIO hats tho, just a question about a niche use-case of your products). I don't know the ideal avenue so you may see a PM on here as well as an email or Twitter thread; am most likely to be found on here, if you end up seeing this :)
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