a snippet from a log at #sdramThingZero - 133MS/s 32-bit Logic Analyzer...

Wherein, I've ordered a Raspberry Pi Zero, and realized I don't actually have a functional display with an HDMI/DVI input...

As you may recall from the previous log-entries at this project, I went a bit crazy in trying to turn an old 15in VGA-input LCD computer-monitor into a multi-input display, by attaching an old plasma-screen's TV-Tuner/Video-processing board...

It worked, sorta, I'll leave the details to the previous logs. But the gist of it is that A) That screen doesn't have speakers, and more-importantly B) The color-bits output by the TV-Tuner board aren't aligned with FPD-Link (the monitor's input to the panel), so, as I recall, where FPD-Link expects the highest bits, the TV-Tuner is outputting its lowest bits. No, that doesn't quite make sense, does it...? Something like that, anyhow. The end-result was that by adjusting the brightness (on the TV-tuner) to 0, the image is about right, but not quite.

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kden.

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Further, I've got a project coming up which needs the circuit (poorly-) converting between the TV-Tuner's single-pixel output and the dual-pixel FPD-Link... Those chips are spendy, so I'd rather not build another, especially since that circuit was designed for the purpose it will be re-re-purposed back to, and only *barely* works with the project it's currently being (re-)purposed for.

Oy, describing these ridiculous display-conversion "adventures" usually seems to be quite difficult.

Anyways here's what I wrote at the log:

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One realization re: PiZero: Yeahp, I don't have a screen with DVI/HDMI input... I think I can hack something together, but it'll definitely be a hack. At one point a couple years back I did a DVI -> FPD-Link converter, it should probably work, but then I need some adapters from Micro-HDMI->DVI, or something... And the micro->HDMI converters were cheap at that place, but not in stock (figures). We'll see where this goes. Oh, and I finally managed to dig out the fluorescent-tube used in #my very first binary-clock (and many other projects, prior)... turns out the ground-wire got ripped from the tube, but luckily the tube is in-tact as well as the solder-point. FHWEW! So, DVI->FPD-Link may be "the path." Alternatively, I have another LCD display to which I once attached an old Plasma's TV-Tuner board... (which also happens to have HDMI inputs). #Ridiculous [LCD] Display Hacks It's a bit hokey (some of the color-bits are misaligned), but pseudo-functional, and maybe worth fixing-right. Oh, and I might be acquiring a "new" PowerBook G4, from a generous (and extremely patient) donor, to replace the old one, whose motherboard died... which means I'll be needing the Single-Pixel-to-Dual-Pixel converter I'd repurposed for the Plasma->LCD converter, to install that 1400x1050 display back in the new PBG4 (1024x768 is painful!)... So, maybe I'll be needing another of those converters. Those chips ain't cheap. Oy. Oh yeah, and I'd need to redesign it slightly to remap those color-bits... if I wanted to do it right for the Plasma->LCD converter. Weee!

no... dagnabbit... if I'm already building a new circuit, rather'n just soldering up a prebuilt PCB... then the logical-conclusion would be to work it for the *other* LCD display, which just happens to have speakers. So, I'd need... Well, that display is dual-pixel, as well, but dual-pixel *parallel*... the TV-tuner board is single-pixel LVDS-output, with, again, a weird color-bit-mapping. So... I gotsta get an LVDS->Parallel converter (which, actually, I think I have a few, just not the ones the *other* board was designed for, savings: $8). But, then, I need to convert the single-pixel parallel-data into dual-pixel *parallel* data... which would need... a couple 8-bit D-Q latches... No, wait... a couple *for each color* (so six) (and I just happened to invest in a bunch of 574's), and... Hmm, something to divide the pixel-clock in half... another D-Q latch should do... Maybe an inverter or some other glue-logic... I might actually already own all the parts I need, only major problem is the tiny pin-spacing of the LVDS-receivers... Don't *really* feel like designing a PCB for this one-off ridonculosity. (we'll call it "art"). Oh, maybe I can get away with only 3 8-bit DQ latches... Why didn't I invest in some 50+pin TSSOP breakouts...? Ah, but there's a TQFP-100 breakout I could cut in half, and only have a few pins hanging on each side to be dead-bugged... Only thing is, how do I assure that it always picks up the *first* pixel on the latch...? (how many pixel-clocks does the receiver take to sync its PLL?). Guess I could throw in a button to inject a pixel-clock (or a few dozen, with bouncing and all) if it's not synced properly...

So, if I've got this straight, I should be able to take an old 15in VGA-input LCD monitor with built-in speakers, and cludge-together a converter to connect an old (dead) plasma-TV's TV-Tuner board... 15in 1024x768 with two HDMI inputs, TV-tuner, VGA (via RCA-jacks!), a couple composite inputs, and a few other doodads. And... then I'll have something I can connect to the $5 PiZero.

So, how do I determine the color-bit mapping...? I *know* it's non-standard, as I spent quite a bit of effort fiddling with the brightness-settings (really low) to get it working with a standard FPD-Link display... So those high-bits are mis-located, is the logical conclusion. I suppose I could drive it with an HDMI source, 'scope the outputs of the LVDS->Parallel chip when driving it with, say, specific RGB-values (plausibly via GIMP?)... But, then, do I need to worry about whether there's color-correction going on via the OS...? Oh, and... I don't actually have a video-card with DVI/HDMI... Though, the "new" PBG4 does... so, hmmm.... But, then, the TV-Tuner has its own color-"correction" via brightness/contrast, as well as temperature, and more... so, realistically, quite unlikely I'll find a 1:1 mapping from in to out...