Framework tablet build for Embedded development

Creators & Developers
1

Hi guys, I have been dreaming to get the ultimate hardware development tablet for embedded development and various other endeavors that I do. So I came up with must have and nice to have list of feature for my build. I will be getting a used framework mainboard as the brain of my built since it makes the tablet nicely modular, which I love. Also the first gen boards are pretty cheap for what they are.

My ultimate goal is to build something inspired by the original framework tablet build but make it more compact, so that I can actually use it in the field. I have MBA and it is a pain when I need to connect it to some random device god knows where to monitor the uart and mqtt at once.

Must haves:
Touch screen
32-64GB Ram
Around 12 inch size
IO (I will incorporate even ethernet if I can)
Reasonable battery life
3D printable + CF/ALU build

Nice to have:
Pen support
Trackball

Research so far:
I have been focusing on finding the optimal screen. I really like the surface pro 4/5 screen. They are very affordable and have support for both touch and pen, however they also have major downsides. Unknown 25 pin connector, but should be eDP. Unknown spi+usb communication for pen and touch respectively.

Alternatively an ipad screen would also be an option, but I would sacrifice quite a bit of screen real estate and touch support is also kinda iffy.

The easy way out is to grab a touch screen kit off of aliexpress with bonded digitizer. There are 12.1 or 11.6 inch screens which seem reasonable, they come with controller board that could be used, however they should communicate over eDP, so it should be possible to use the framework eDP interface.

I plan to use one of the mainboard usb ports for internal stuff, touch and additional IO. I would love to have pen support but that seems highly unlikey, unless the surface screen would suddenly become completely documented. This will leave me with three io port of which I might route one to the top or the bottom of the device, to keep it compact.

Useful links:
Surface pro 4 screen reverse engineering

Aliexpress 12.1 inch display
https://a.aliexpress.com/_ExTJOet

2 Likes
2

One more display possibility is to grab 12.5 inch eDP LCD, there are some 1080p options available on aliexpress and ebay, however then I would have to bond the digitizer to the display, which I would like to avoid, since it requires dust free work area and steady hands. Unless the existing touch interfaces on the lenovo x2xx screens have been reverse engineered.

1 Like
3

It seems smaller screens, such as those, are often 2 lane eDP. Have you seen this thread with an adapter that a community member created? 40pin eDP (Framework/4Lane) to 30pin eDP(2 lane) - #13 by Dylan_Evans

4

Yeah, I wanted to add it to the reading list, but I am limited to two links in a post for now.

Ideally I hope to adapt the edp interface and get rid of the conversion board to save space. Sadly there is not much info in the screen listing, but it seems that they are using fpc for the edp, so I can just design a pcb that converts it to the framework edp cable connector.

5

Something like this digitizer might also give me the wacom pen support which would be awesome, although I am not 100% sure it would work with any screen due to metallic layers.

And there is even a guide on how to get it to work :slight_smile:

https://blog.muwave.de/2014/02/wacom-digitizer-screen/

6

Actually this assembly might work with the 30 pin adapter, but the resolution is not great, it is wxga, so 1280x800.

7

I found Surface Pro 4 schematics, there is a youtube video with download link in the description, maybe there is still hope for the surface screen. Although I would still be worried about reverse engineering the spi and i2c communication protocols for the touch and ntrig, but I think there are linux drivers for it so maybe there is hope.

I had to reverse engineer spi communication once when I was still intern at work, but that was not a plesant experience :rofl:.

This seems to be the sp4 edp pinout

IMG_0920
IMG_09202388Ă—1500 452 KB

It does seem to be correct this is the ribbon for the sp4 lcd and it is 2x25 pin, but I don’t know the connector type, it looks like a some mezanine connectors that I’ve seen, but nothing specific rings a bell.

IMG_0921
IMG_09211076Ă—1046 66.5 KB

8

Actually this connector might be it based on the second number in the schematic, pitch seems plausible.

https://cz.farnell.com/molex/51338-0574/mezzanine-connector-rcpt-50pos/dp/3500601

9

Got a notification about this post as my own topic was linked, just had a quick read through the topic - you seem to have a good level of experience but I would (from personal attempts) strongly advise against trying to bond your own digitiser. If you are considering OCA film you need a dust free environment (as you said) - which can be achieved with filtered airflow - but more importantly you need a bubble free finish, and this is only realistically achievable with a debubble (autoclave) machine. You can use LOCA glue, but it is messy as all hell and the screen I did got all screwy a few weeks later (I think I didn’t cure it long enough).

3 Likes
10

Yeah that’s exactly what I am worried about, I could do dust free with difficulty, but the bubbles and aligning everything perfectly would be an issue.

11

I did some more digging through the surface pro 4 schematic. I’ve found the touch connector and it’s pinout, it looks like the spi and and i2c are connected directly to the processor, would there be any way to do it on the framework motherboard or should I look for a suitable ftdi chip. I am not sire the drivers would work if I go the ftdi route.

IMG_0925
IMG_09252139Ă—858 272 KB

IMG_0924
IMG_09242006Ă—1377 424 KB

IMG_0923
IMG_09232170Ă—1328 551 KB

Oh and one more thing, it communicates using 1.8v

12

I have found a control board for the SP3 screen, so that might also be an option.

https://a.aliexpress.com/_ExUoLel

13

Hi I’d very much like a framework tablet that could use a wacom stylus. My original idea was to 3d print a framework “backpack” for a samsung s9 tablet (same thickness as the touchscreen used for the original framework tablet). The only thing is you’d have to use 3rd party software to be able to use android with the framework and the one I know of is designed for windows. There is also the asus pro art, which is also windows only. If you guys can figure out how to get an old surface pro screen to work that would be way better.

14

I tried to post on the surfaceLinux reddit, if there is somebody with the knowledge of the i2c and spi protocols that the screen uses, so maybe I will get some info there. Support for it was developed for the as part of the surface kernel, so hopefully I will get some info.

If I know the protocol, but I can not get it to work in windows with the drivers, there is always the option to use a microcontroller like an stm32 process the data from i2c/spi and just push it to the device as hid through the usb.

The i2c could just be HID over I2C, in that case there is an FTDI chip exactly for that, but that still leaves the spi on the table. SPI is supposidely used for the pen data.

I will probably have to make my own adapter from framework edp to the surface edp, since the connector they used is pretty exotic in combination with edp, at least on aliexpress, so this might get costly, however I am thinking about a simble flex pcb with both connectors and then I will just hopefully make it work somehow :smiley: and for the touch either ftdi or the stm32, we will see.

15

Small status update, I decided to try and lay out a small adapter pcb, I have only the edp signaling ready. I’ve tried to stick to NXP displayport layout guidelines so all traces for diff pairs are length matched, the guide says to keep it withing 5 mil, I managed to route them to within 1 mil of length. However, signal quality will be questionable at best, lets just say that the pcb looks like abstract art, since the pairs are crossing on the pinouts. I have to figure out the rest of the connections, mainly for the backlight. But I will check the other adapters here on the forum and hopefully figure out the rest.

One questionmark is the i2c interface comming from the LCD, it is definitely not touch, hopefully it can be left disconnected, otherwise there would have to be some more logic to handle that.

Screenshot 2024-02-05 at 17.09.36
Screenshot 2024-02-05 at 17.09.361398Ă—828 137 KB

Screenshot 2024-02-05 at 17.09.27
Screenshot 2024-02-05 at 17.09.271344Ă—992 325 KB

1 Like
16

You may find that the I2C interface is what communicates the LCD details (resolution, size, etc) to the video hardware. This was a scheme introduced in VGA displays a long time ago, and I suspect it continues on to current production displays.

17

Yeah, I am worried about exactly that. With MIPI, it sometimes is not needed, but not sure about eDP.

18

I am starting to look at other options for LCDs too. Lenovo screens are good candidates, since they have pen support.

The MIIX replacement LCDs are really nice, although they run about $150. There is also the ElitePad 1000 G2 which is 10 inch but has 30 pin edp + i2c for touch and pen.

One more thing: video about hacking the wacom digitizer https://youtu.be/Zsaeg7UrHr4?si=KFLD7hjgeFHo99rB

It would be lovely if there was touch lcd compatible with the digitizers, since the protocols seem relatively documented and are available cheaply on ebay.

Finally schematic dump on the ElitePad LCD since there are schematics on iFixit website

IMG_0929
IMG_09292189Ă—1128 161 KB

IMG_0930
IMG_09301424Ă—1004 119 KB

1 Like
19

This is true for VGA/DVI/HDMI, but it is false for DisplayPort and eDP panels specifically. With those, the AUX channel is used for all such communications instead. The I2C interface on that LCD is more likely to be for features like eSOL (instant on logo, apparently?) or DDS (no idea what that is but shows up in TL070FVXS01 datasheet). Of course, there might still be a DDC interface on that I2C, but it’s not a guarantee by any means.

What I’d recommend is connecting the panel I2C, but through jumpers you can cut, or maybe add two resistor footprints that you can populate later.

20

It seems like the project might be on hold until I find some other framework motherboard for sale in EU, since the seller stopped responding :confused: