LCD in "low power" or half resolution mode??

[likwidoxigen]

Hey all, my search skills apparently suck on forums. I can't find anything about the low power or low resolution mode on the LCD to conserve power anywhere. I know there were like 3 freaking threads about it too. If any of you could link me that would be great.

 

[Chip]

I don't think there were any threads with this specific topic here. There isn't exactly a "low power" mode, though you can lower the brightness to save power if you wish.

LCD panels only have one set resolution. Programs that use different resolutions must be scaled up or down to match. This does not really affect battery life one way or the other.

 

[likwidoxigen]

I'd swear that the LCD had a mode that flipped off half the pixels and dropped the resolution to 400x240. With the pixel pitch (from a reasonable viewing distance) it wouldn't matter too much and should (in theory) save a fair bit of power.

Did I really make this up in my head? I'd swear that it was possible... (though i've had some crazy dreams latley)

 

[Tor]

What uses power in the LCD screens isn't the pixels, it's the backlight. Unless it's a transflective screen (which uses sunlight for the same thing) you won't see a thing without the backlight. In these 800x480 screens the backlight is generated from a number (3-5) of white LEDs which are mounted at one edge (usually one of the short edges). To the backlight it doesn't matter how many pixels are in use.

 

[likwidoxigen]

What uses power in the LCD screens isn't the pixels, it's the backlight.

Valid point. I forgot about that.

Maybe i read it in context of speed/performance for only having to buffer half the data?

 

[maciek_urbanski]

What uses power in the LCD screens isn't the pixels, it's the backlight.

Valid point. I forgot about that.

Maybe i read it in context of speed/performance for only having to buffer half the data?

Mode you're referring to does in fact exist but not in LCDs. It's used in OLED displays of most cellular phones. OLEDs emit light and have no backlight, so the display itself is a major consumer of power. In order to conserve it there is mode in driver that turns off all but small strip of display. This means that even driver itself shuts down part of logic responsible for maintaining most of OLED area. Usually this strip is used for displaying clock and some icons.

 

[dekutree64]

Is this the post you were thinking of?

 

[Chip]

Is this the post you were thinking of?

That's probably the post the OP was thinking about. What that mode does do is allow you to work with a smaller framebuffer (taking less memory and having to do less work) and the display scales the quarter-rez image for you. It's great for getting a free upscale for 320x240 GP2X ports, but it doesn't do much for your battery life

 

[likwidoxigen]

Is this the post you were thinking of?

THAT'S THE ONE!!!!!!

And the reason I was thinking of power savings was from being able to underclock the processor a ton with the savings on not having to software scale the bitmaps and not have to use the 3d hardware.

So the powersaving idea was unrelated to the actual LCD, but yes that's the exact post I was looking for.

 

[t.s.]

How about using e-paper for the display? Like one in use on OLPC-XO1? (http://en.wikipedia.org/wiki/OLPC_XO-1) or we can use current technology on e-paper (www.pixelqi.com/home)? Guess it can cut the power on half or more..

 

[Capn_Fish]

That would kind of defeat the "gaming" purpose of the Pandora. Don't those displays have horrible refresh rates (as in 0.5 seconds or something)?

 

[t.s.]

oh, I don't think so (if what they said were true):

EPAPER LOOK - WITH COLOR AND VIDEO
The XO screen is sunlight readable, but hard to read in dim roomlight without the backlight on. Pixel Qi has new inventions that can transform this situation. The screen with the backlight off can appear as bright and crisp as paper, but also supports full video speed playback and color. The paper-like look to the screen is desirable. We want to be able to comfortably read off of our screens - with this innovation we finally will be able to.
(http://www.pixelqi.com/products)

full video speed playback == full frame-rate-on-game, rite?

OOT: dunno if XO have this kind of advantage too (full video speed playback).

PS: You can get more info from the link in my previous posting (all you need is time to read it :wink: )

 

[likwidoxigen]

How about using e-paper for the display? Like one in use on OLPC-XO1? (http://en.wikipedia.org/wiki/OLPC_XO-1) or we can use current technology on e-paper (http://www.pixelqi.com/home)? Guess it can cut the power on half or more..

The OLPC XO actually doesn't use an e-paper display. It's just has two modes, a reflective and a color mode.
An e-paper display is what's used in the Amazon Kindle and Sony E-book readers.

It would be pretty sweet to incorporate and e-paper display on top of the clamshell for things like rss feeds and e-books, though it would be well beyond anything I could hope to do.

 

[fischju]

It's the Open Pandora, you could add one if you wanted. The board is capable of driving 2 1920x1200 displays.

 

[t.s.]

The OLPC XO actually doesn't use an e-paper display. It's just has two modes, a reflective and a color mode.
An e-paper display is what's used in the Amazon Kindle and Sony E-book readers.

The first-generation OLPC laptops have a novel low-cost LCD. Later generations of the OLPC laptop are expected to use low-cost,
low-power and high-resolution electronic paper displays. <-- Yep, miss it. TQ for the correction.

 

[likwidoxigen]

It's the Open Pandora, you could add one if you wanted. The board is capable of driving 2 1920x1200 displays.

I'm sure someone could add one (notice I said that already). BUT I don't have the ability to do so(notice I said that too).

The first-generation OLPC laptops have a novel low-cost LCD. Later generations of the OLPC laptop are expected to use low-cost,
low-power and high-resolution electronic paper displays. <-- Yep, miss it. TQ for the correction.

Heh, they'll also be running windows. Such a shame that the device would have to deal with the kind of bloat. Sugar was such a cool idea too.

 

[Chip]

How about using e-paper for the display? Like one in use on OLPC-XO1? (http://en.wikipedia.org/wiki/OLPC_XO-1) or we can use current technology on e-paper (http://www.pixelqi.com/home)? Guess it can cut the power on half or more..

The OLPC uses a standard transflective LCD display. E-paper is good for books, but you would never want to use it for anything with movement. Most e-paper displays take several seconds for each screen refresh. Obviously no good if you want to play games or watch videos.

Add to that the facts that e-paper is considerably more expensive than LCD, is not commercially available in color, is not backlit, and the Pandora is set to go into full production any day now (major design changes have been closed for more than six months), and I think it's safe to say that it's not an option. :wink: