Digital Video Out

[jscinoz]

Hi,


From what I've gathered, the OMAP3 chipset shared by the Pandora, BeagleBoard, Gumstix, and I'm sure others, has one digital and one analogue video output.

I know that on the Pandora, the digital output is connected to the internal display, but I'm wondering if it would be possible to hack in a HDMI connector (but really DVI-D like on the BeagleBoard) and add a physical switch, to toggle between the board's digital output going to the internal display or a digital output. Obviously the internal display an a proposed digital output like this couldn't be used simultaneously, but switching between the two should be possible with a physical switch.

Would something like this be possible?


EDIT: Assuming that this is possible at a hardware level, it should be easy enough to wire the switch to also generate an ACPI event, so it'd be easy to have xrandr change the resolution when the display is switched.


Thanks,
jscinoz

 

[Chip]

It's not impossible, but it is an incredibly complex and possibly destructive mod. It's definitely beyond the capabilities of anybody without significant EE experience.

 

[JayFoxRox]

I was suggesting the same for month because this would improve the pandora ALOT for me. It would make it possible to use it for stationary use too which is alot better for drawing stuff etc or programming directly on the pandora.
I also planned to do this, but it seems to be pretty hard and I wouldn't do it unless I had 2 or more Pandoras.

 

[benjymous]

Is the signal sent down the ribbon cable all ready too specific to the screen to be usable? (Could we just unplug the cable, connect it to something that can convert that back to VGA, and passthrough the ribbon back to the LCD?)

 

[Chip]

Could we just unplug the cable, connect it to something that can convert that back to VGA, and passthrough the ribbon back to the LCD?
Not exactly. There are digital framer chips that can convert the raw digital data into something useful, but you can't have the LCD panel and the framer connected at the same time. What you would need is a board that can switch ~30 signal and control lines (without introducing any interference) between a cable that goes to the LCD panel and a circuit consisting of a framer chip and buffer array to convert the voltages.

I don't think this could be done internally, and externally isn't an option either. I think this would actually require a full case mod to make room for all the new circuitry, not to mention the physical connector for whatever video format to which you're converting. Like I said, it's not impossible. But it is close enough to impossible as makes no difference.

 

[tsh]

For the cost and effort, a beagle board has to be not much more expensive - and it would presumably be fairly simple to use the pandora as a controler - either exporting the display to your tv-top hardware, or running an app on the beagle and using the pandora keyboard. I guess any app should run on either platform with no porting effort? Having the TV detect when you come in range, and pick up the display wireless would be cool...

 

[jscinoz]

Hmm, thanks for the information, I wasn't really sure how the signal to the internal screen was sent.

Since the method of doing this is as complex as you describe, its probably just a tad beyond my skills

 

[EdCa22]

Could we just unplug the cable, connect it to something that can convert that back to VGA, and passthrough the ribbon back to the LCD?
Not exactly. There are digital framer chips that can convert the raw digital data into something useful, but you can't have the LCD panel and the framer connected at the same time. What you would need is a board that can switch ~30 signal and control lines (without introducing any interference) between a cable that goes to the LCD panel and a circuit consisting of a framer chip and buffer array to convert the voltages.

I don't think this could be done internally, and externally isn't an option either. I think this would actually require a full case mod to make room for all the new circuitry, not to mention the physical connector for whatever video format to which you're converting. Like I said, it's not impossible. But it is close enough to impossible as makes no difference.

Uh, hwell, ok. I'm going to come clean here- I designed a pcb capable of this some time ago and left significant hints about it in a thread in the developer section. I am currently on holiday so don't have access to the schematics,but I don't think it is any bigger than 30x40mm (pretty sure its much smaller but this is a generous estimate),based on an expansion board from gumstix. It is a 3 layer board. It uses 1 Gpio line,but this is not really necessary and there is one on the LCD cable anyway.it has a place for a connector on the very edge of the board for the LCD cable from the motherboard and another directly above on the other side of the board for the connector to the real LCD. The hdmi/dvi socket is not on the board but would be connected by wires. So it is perfectly possible,and actually was only a couple of hours work. Trouble is,I can't make one until someone gives me the LCD pinout and part number so I can shift the pcb around and finish the design (so pcb may get bigger or smaller too),which so far I have seen no signs of despite asking.plus I do not know if it will fit in the case.also,as far as I know,if both LCD and dvi monitor support the same resolutions it will output to both simultaneously. Also,as chip says,perhaps I need to add a level shifter ala beagleboard, but I do not know until someone tells me the LCD voltages etc.

Edit: I'm at a real computer now, so don't have to contend with the iphones screen size and on screen keyboard (come on pandora, you'd make holidays so much easier!). Just wanted to add that you don't need a chip to switch the signals because the 'DVI encoder' tri-states its inputs when you change its enable line...which is what youd use the GPIO, or a switch, for. Also, as detailed in my original thread on this, I'd need a bunch of other stuff to get the voltages I need unless they are available internally on the motherboard already. I designed this to try and make it fit given what I have seen from pictures and videos of the positioning of the LCD connector on the motherboard, but there may still not be enough room... however, it occurred to me last week or so (when the videos of the LCD installation into the case were made) that it might be possible to put the DVI circuit inside the LCD housing, to the left or right. Don't know where you'd put the DVI connector in that case though.. and I suspect that the pandora guys would be even less willing to give away the pin out for the LCD itself rather than just their cable (cable going into LCD is different to that coming out of pandora mobo) as they may not be allowed (NDA for LCD part?). The board I based the design on is the overo earth's summit, which made it very easy to design, and looking at that now I'd say the board I designed is about 20-30mm by just under 40mm so my estimate above is about right...however some re-jigging may make more room - as I said I didnt spend an awful lot of time on the design. But unless the information becomes available from the guys this is all irrelevant! A little help?

 

[dispraekailo]

I suggest looking into a handy xserver called 'freeNX'. It allows you to host a desktop environment which is accessible over lan (much like the standard X windowing system), but has a lot of handy features. I use freenx to access my two linux workstations through my windows pc, and can easily resize my linux desktop just like any other application in my windows environment. Keyboard and mouse support works by default too.

FreeNX is probably the best choice for home workstations that will be integrating with the pandora, as you can easily interface over a wireless connection. It's not nearly as portable as a digital video out though, given that you need the freenx client installed on any machines that will be serving as a terminal for the pandora. However if you have even the cheapest of laptops, it's perfect. You can take advantage of the much larger display and keyboard, while using the pandora to do all the rendering work.

Though consider the reverse once--accessing your home workstation from your pandora on the go! I can see it already.. using a bluetooth keyboard to type up code, compiling on my quad core at home, and syncing to my svn repo once it's done faster than I could compile on the pandora itself...


*sigh* The things I fantasize about.

 

[jscinoz]

EdCa22, I wouldn't have thought that something as basic as the pinout for a component would be restricted under a NDA, but I'm in no position to know for sure

dispraekailo, This topic is more about hacking on a digital video output somehow, not remotely accessing applications/an entire session. Although, if I really wanted to access things running on my other boxes from my Pandora, I'd much sooner use Xpra (basically its screen but for X11 apps), or plain old ssh X11 forwarding than NX, as AFAIK NX is basically for accessing an entire session remotely, when I'd only need to access single applications.