Second screen add-on project

[Exophase]

So, this came up a few times already as an idea, and I recommended someone start a thread for it. Since then I've talked a bit with an electrical engineer coworker who might be interested in helping out with something like this, so I might end up trying to do this with him at some point.

Just so we're clear, this is about adding an external second screen to Pandora (and down the road Pyra), it's not about doing any kind of new handheld with two screens or getting ED to make this. Think of it more like a hardware mod or homebrew sort of thing, although it wouldn't actually modify the handheld and could be used with other devices. It's also not really meant to be anything serious, I get that most people wouldn't be very interested in something like this. This thread is just for coming up with ideas for those few people who do think this would be interesting.

Here's what I'm thinking thus far:

1) LCD display 2.8" diagonal, that can be programmed with a direct bus interface (probably means has a framebuffer), I'd prefer 256x192 for nice DS integration but you can't really find that. Having to rotate to go from 240x320 to 320x240 isn't a big deal.

2) Should also have a resistive touchscreen.

3) All communication and power would be over USB 2.0. This should be enough bandwidth to facilitate 320x240x24bpp or at least 16bpp @ 60Hz, along with touch information going back. Possibly using isochronous mode, trading possibility of errors for bandwidth/latency (probably in practice there won't be many errors?)

4) Needs a microcontroller with USB, a lot of SRAM to store double buffered 320x240 framebuffers, and some ADCs to read the touchscreen values.

5) I'm not totally sure on this yet, but I think at least to start with it'll attach to Pandora by being laid on top of the nubs and some of the keyboard, and kept in place with an elastic band (if necessary, with holes cut out for the controls and maybe some of the keyboard)

For LCD I'm thinking this:

http://www.mouser.com/ds/2/116/DT028ATFT-v21-221378.pdf

And for microcontroller:

http://components.arrow.com/part/detail/62024492S651017N2064?region=na&utm_source=FindChips&utm_medium=buyNow

I like this one because it has 512KB of SRAM, USB 2.0, a parallel bus interface for LCD, and you can get it in a 64-pin TQFP package so it's not that unrealistic to assemble by hand.

Any thoughts?

 

[mcobit]

This sounds like a nice idea.


you could also use a lcd that just has component input and power it over usb.


Edit: But I guess you want crisp pixels


Edit2: I thought of attaching a bigger (around 7") lcd and use the Pandoralcd as the touchscreen. But that might be hard to hold and control. Might try that sometime.

 

[elwing]

hum, why not a real DS screen, not long ago it was pretty easy to find spare DS lcd and cheap too and with a touchscreen... not sure if the protocol have been documented through and I have no idea if it got framebuffer trough I supose it doesn't...

and since we're already using some Cortex why use a pic when you can go with something like a Cortex M4 or such?

 

[levi]

The microcontroller's needed to talk to the USB port and to convert the USB stuff to the LCD stuff. It doesn't really matter what microcontroller you use for that, though little hobbyist CPUs like PIC and Arduino are often easier to wire up. I'd assume that's also where the framebuffer's located logically rather than on the LCD though I don't know to be fair.

 

[slaeshjag]

It does matter what microcontroller you use. You need to shuffle around 10+ MB/s and have half a MB of built-in RAM for double buffering. And a USB 2.0 port. And enough grunt left over to handle the USB port. With those requirements, you're right on the edge between beefy microcontroller and SoC. Exophase dragged me along a little on his parts hunt for the microcontroller, he didn't choose that microcontroller at random

 

[moxie]

You're all insane, in a very good way I can't contribute much to the practicalities, but I can do a good cheerleading thingie from the sidelines

 

[Foxgod]

I am actually interested, i would plug it in every time i launch a ds game

But it would also be great to manage a music list while the panda/pyra are closed.

I would be nice if it could be used to raise /lower volume, skip to next song, etc.

Howabout making it a screen attached to a wire, so you can handle it like a pocket watch? or a handsfree headset.

If it would be directly attached it would turn the pyra into a weird moloch, unless it can be attached to the lower side below the keyboard, somehow.

If you want to attach it to the lower side of the panda, you could make a case that clicks to the bottom (battery side) of the panda/pyra, that got an usb 2.0 wire running trough it, so it can connect at the back, and in front of the case could be a holder for the screen.

 

[Hồng Thất Công]

Oh!  Exo!  You read my mind.  Please make this a reality!  Are you think of selling these when it's done?

 

[Exophase]

hum, why not a real DS screen, not long ago it was pretty easy to find spare DS lcd and cheap too and with a touchscreen... not sure if the protocol have been documented through and I have no idea if it got framebuffer trough I supose it doesn't...

It's too large, and I need something with a built-in controller/framebuffer.

and since we're already using some Cortex why use a pic when you can go with something like a Cortex M4 or such?

Cortex-M3 or M4 was my first choice too, but currently they top out at 284KB of SRAM.

I thought about trying to synchronize USB with frame output to try to avoid having double buffered framebuffers on the microcontroller but I really don't know if that's realistic, plus it could increase the burden on the host..

Oh! Exo! You read my mind. Please make this a reality! Are you think of selling these when it's done?

The goal right now is to make it simple enough that other people could make one, with the drawings and software source available. Not sure if it'll mean I can make them or not. Of course we're far from that point anyway, first step would just be to see if the basic concept works, using an eval board and some hand-soldered up cables.

 

[spud42]

when you first mentioned this idea my first thought before you mentioned the size screen . i immediately thought of this sort of screen.it would have to be rehoused as a clip on to the pandora lid and could use the existing TV out of the pandora.

something along the lines of this... excuse my poor skills...

http://my.ebay.com.au/ws/eBayISAPI.dll?MyEbayBeta&MyEbay=&gbh=1&guest=1

http://www.ebay.com.au/itm/3-5-TFT-LCD-Color-Screen-Monitor-For-Car-Rear-Reverse-Rearview-Camera-DVD-/321166194236?pt=AU_Car_Parts_Accessories&hash=item4ac6ff363c

this screen may be too big but they can be found in 3 1/2" and 4" sizes i think... and cheap enough that its not too expensive to test.

Drastic would work just as it normally does with a TV at home....

powering it might be the problem. they say that it requires 12v but i have seen Ben Heck use a screen like this in a raspberry pi portable ( i think) and found it will operate at around 6.7V

 

[Hồng Thất Công]

I've tried it

http://boards.openpandora.org/topic/14177-tv-out-directly-from-motherboard/

 

[Askarus]

I've tried it

http://boards.openpandora.org/topic/14177-tv-out-directly-from-motherboard/

That's awesome.

Is there really enough room behind the LCD to fit a second PCB in?

 

[Hồng Thất Công]

I've tried it

http://boards.openpandora.org/topic/14177-tv-out-directly-from-motherboard/

That's awesome.

Is there really enough room behind the LCD to fit a second PCB in?

Very very tight, but yeah it does fit

 

[Askarus]

Always wanted such a thing.

Let's make a deal for Pyra: You tell me how to do a screen addon and  I tell you how to build a cool Pyra suitcase.

 

[Grench]

I wonder...

It may be too far of a sideways trip, but the requirements you described are pretty much a Palm Tungsten era screen isn't it? Maybe able to get the parts cheap(er) by cracking an old case?

 

[Exophase]

Palm Tungsten actually has a 320x320 or 320x480 screen, and 16-bit instead of 18-bit, so not really a good fit for this. Besides, the screen I linked isn't really that expensive (http://www.mouser.com/search/ProductDetail.aspx?qs=zkctU4NzKYcsFZL6aQPNHQ%3d%3d&utm_source=findchips&utm_medium=aggregator&utm_campaign=758-SDT028ATFT-TS&utm_term=DT028ATFT), I'd rather no one had to cannibalize hardware for this.

 

[elwing]

hum, why not a real DS screen, not long ago it was pretty easy to find spare DS lcd and cheap too and with a touchscreen... not sure if the protocol have been documented through and I have no idea if it got framebuffer trough I supose it doesn't...

It's too large, and I need something with a built-in controller/framebuffer.

hum, does that means that there is a framebuffer? (sorry, not really knowledgeable there...)

"7 gsp frame sync"

http://electricstuff.co.uk/ndslcd.html

still a 3.0" screen trough...

edit: additional infos here => http://home.comcast.net/~olimar/DS/jumbotron/

 

[Exophase]

If the original DS screen is really like that Sharp part listed (http://www.premier-electric.com/files/Sharp/LQ030B7DD01.pdf) then the interface is pretty low level, not something I can drive without a display controller.

Although the LCD datasheet I linked doesn't say an awful lot, the product page says that it uses this chip as a controller: http://www.newhavendisplay.com/app_notes/ILI9341.pdf That makes things a lot easier.

 

[elwing]

hum, I just stumbled upon this:

http://www.seeedstudio.com/depot/28-USB-TFT-Display-Module-For-Raspberry-Pi-p-1699.html

 

[Exophase]

Wow, good find, that does look close to what I was going for. It looks like they're using an STM32 with only 20KB of RAM, and the blit commands pretty much write directly to the framebuffer-based LCD (which I can't find a datasheet for). I don't really know how it accomplishes synchronization/avoids tearing - if it does at all. Doesn't look like the source for the firmware is available, which is a shame since it lacks some features I'd want. Dumping and reprogramming the firmware should be straightforward, at least.

I guess it's worth ordering one of these and seeing what I can push through it as it is.