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120hz 1080p or 1440p mobile phone or laptop LCDs?

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120hz 1080p or 1440p mobile phone or laptop LCDs?

Postby RLBURNSIDE » 28 Feb 2017, 00:13

Hi guys, has anyone here tried this phone?

http://www.theverge.com/circuitbreaker/ ... hone-japan

Apparently it's only available in Japan. But if it's got decent transmissivity it might be a good contender for a DIY 1080p native 120hz projector. And if it's even good enough still, maybe using two, one in front of the other, and get 1M:1 contrast ratio too.

I've been looking into cheap ways to get 120hz at 1080p in small sizes (13 inches or less, the smaller the better), but it's really hard to even find legit phones or tablets which have them, let alone be able to take them apart to DIY a gaming projector out of them.

There's this new LG G6 phone with Dolby Vision HDR:

http://www.avsforum.com/lg-g6-smartphon ... ision-hdr/

Some Mediatek phones have 1080p / 120hz but I can't find any to buy in North America or online anywhere, and of course sourcing those LCD panels is next to impossible. The other option is just buying a replacement laptop screen with 120hz over eDP but who knows how hard it will be to find a DP -> eDP connector board.
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Re: 120hz 1080p or 1440p mobile phone or laptop LCDs?

Postby Chief Blur Buster » 28 Feb 2017, 11:12

At CES 2015, I saw 120Hz LCDs being tested with in smartphone factor:

Image

From what I know, several 60Hz LCDs can be overdriven to at 120Hz frequency with few effects. Someone overclocked a 60Hz laptop LCD to 180Hz successfully in an unmodified way.

Also, if you know enough advanced electronics programming, you can use an OLED panel and run a rolling scan on it -- that's what several VR manufacturers (including Oculus) did, with a custom panel controller electronics. Clocked a smartphone 60Hz OLED at 90Hz and utilized a rolling scan on it, in order to lower its persistence to ~2ms.
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Re: 120hz 1080p or 1440p mobile phone or laptop LCDs?

Postby RLBURNSIDE » 04 Mar 2017, 11:01

I'm interested in these phones to make a DIY gaming projector out of them (ideally 120hz if not 1440p or 4K).

This is currently the hottest mobile screen in terms of specs in the world I believe:

http://www.avsforum.com/sony-reveals-xp ... dr-screen/

Native 10-bit and HDR, though likely not support 120hz at 1080p although who knows. Though being LCD means the CR is probably only like 1000-2000:1 max so the home-theater HDR performance will likely be mediocre (unless I can get dual modulation going for mega contrast). But poor HDR is still better than none and if I had to choose, I'd pick 4K + 60hz + HDR over 1080p + 120hz + SDR.

There's no reason I can't build both though, it's just I can't actually buy those 120hz mediatek mobile phone screens, let alone those mobile phones at all!!

If you know of a link to buy either a 120hz 1080p mobile phone panel (with HDMI board) or even the phone itself (maybe it uses eDP or MIPI so another adapter might work), that would be helpful. Or even have any contacts in LCD panel suppliers.

Mobile phones still have good use for LCD since HDR is more efficient (for now) than OLED, although of course OLED + low persistence is beautiful due to the high contrast I just need a transparent light modulator for my use. A tiny screen to me is not really super awesome to game on compared to my 138 inch projected image. I'm just tired of 1080p60hz and need to upgrade to something else this year. There are virtually no 120hz native input projectors on the market still, even in the era of HDMI 2.0a compatible inputs which can easily support it from a cable bandwidth perspective.
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Re: 120hz 1080p or 1440p mobile phone or laptop LCDs?

Postby Chief Blur Buster » 04 Mar 2017, 18:26

Indeed, you will need an LCD if you want to build a homebrew projector.

Try a few 60Hz LCDs and then overdriving them to 120Hz. I think it is quite doable with a custom circuit. You might lose 10-20% contrast ratio during the overclock.

Also of possible interest:
Chief Blur Buster wrote:Mechanical Spinning-Disc Shutter To Lower LCD/LCOS Projector Persistence:

You can mechanically lower the persistence of an LCD/LCOS projector with mechanical rolling shutter. It is possible to strobe a projector for low persistence by using a spinning disc with a slot -- like a blacked-out colorwheel with a white area. Mechanical rolling shutter to lower LCD/LCOS projector persistence with non-modulatable HID source. Experiments have been done with a spinning variable-speed fan (with black blades) in front of a projector lens -- and it does produce blur-reducing effects to off-the-shelf LCD projectors.

You build a VSYNC-synchronized motor instead, with a plexiglas disc that's blacked out except for a small slot (percentage of disc black = percentage reduction of motion blur, 75% black pie = 75% reduction in LCD motion blur) -- like a spinning pie chart -- 75% black, 25% clear -- for a 75% reduction in LCD motion blur from your projector. GtG leakage between LCD refresh cycles is still a problem, creating the double-image strobe-crosstalk depending on strobe phase (timing of shutter scan relative to timing of LCD GtG scan, as seen in high-speed videos of LCD scanouts).

The mechanical rolling shutter should be as far away from the LCD GtG zone as possible, preferably 180 degrees out-of-phase of the LCD GtG scan, e.g. 1/2 screen height away from the GtG blur zone seen in high-speed videos of LCD refresh cycles (that is, the blurry "wipe effect" from top-to-bottom, seen in the non-strobed section of the high speed video of an LCD). Like a scanning backlight, except with a mechanical shutter -- you're making the fully refreshed part of the LCD visible in a rolling-shutter fashion, as the GtG zones occurs hidden by the mechanical shutter. Use potentiometers/adjustments to allow you to calibrate motor synchronization phase relative to VSYNC signal (either tapped into the cable, or tapped some appropriate solder joint).

Note, you'll be spinning the rolling shutter motor 3600RPM for 60Hz (60Hz x 60s) and 7200RPM for 120Hz (120Hz x 60s). Multiple clear zones (e.g. 4) can allow you to spin wheel slower (e.g. 1/4 speed) instead. Make vibrations are well-damped. Ripping out and modifying an existing DLP colorwheel motor+disc (one that already has clear zone, and blacking-out the colored sections with some kind of thin lightweight opaque paint/film) is also an alternative approach if you can fit the projector aperture on such a hacked spinning disc.

An additional idea -- a 120Hz projector LCD/LCOS does have the advantage of doing a 2-pass scan for a cleaner 60Hz strobed LCD -- one can scan the LCD twice in darkness to clean up the LCD GtG as much as possible -- then do a chasing strobe sometime behind the 2nd pass scan -- this can be much simpler for DIY electronics hackers than trying to create high-quality LCD overdrive tables that are strobe-optimized (this can be extremely difficult to do) -- the stuff of NVIDIA LightBoost/ULMB fame is often devilishly difficult to do, but the 2-pass LCD scan is quite simple and can help slower-responding non-overdriven LCDs to look cleaner when strobed.

For best persistence-lowering quality (less double-image effect -- strobe crosstalk) you want a projector with relatively fast LCD GTG response in milliseconds preferably far less than half a refresh cycle -- preferably one-quarter, especially if you plan to do single-pass refresh before strobe. Finding a fast responding small LCD/LCOS can be difficult to find, but it's a consideration worth keeping in mind.

You can even make this optional -- stop the spinning disc or move the disc out of the way -- to go back to full-brightness full-persistence mode, whenever you don't need a low persistence mode for your projector.

For more information about DIY strobed display experiments, see Electronics Hacking: Creating A Strobe Backlight
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