EEVblog Electronics Community Forum
Electronics => Microcontrollers => Topic started by: legacy on January 13, 2019, 03:22:46 pm
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for a do-it-yourself project I'd like to combine an LCD-screen with graphics tablets with the purpose of converting it into a graphics tablet-screen hybrid.
I don't need colors, green is OK (and preferred), and I don't want to have a light inverter because it produces heat and this is a thing I'd like to minimize.
I already have several old Wacom tablets board, some are damaged, some are completely destroyed, but in a stack of 10 boards ... 1 got completely restored to fully and aesthetically functionality (I have even polished the plastics), and 2 boards are ... well "acceptable", the plastics are really bad, glued here and there, but they work.
So I want to modify one of the two "acceptable" Wacom tablets and have an integrated LCD.
Now, for this crazy purpose, I need a very thin LCD screen (max 9mm), without metal on the back, and backlighted by LED rather than by neon.
eInc LCDs look perfect, but I need
- VGA input, say 800x640@50-60Hz is OK
- no components or metal on the back of the glass
- leg backlight (no neon+inverter)
- the maximal thickness of the whole (frame + glass + led backlight) must be inferiorior to 9mm
I am open to hints ;D
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You should probably study first to know what are you diving into, rather then quickly slapping together ideas, while not having any clues of how those work.
Do you know what a refresh rate of eInk is? How their service life is affected by the number of refreshes?
Do you know what a VGA signal is? How to convert it to digital? How to put the digitized VGA in the eInk display, which will more than likely have a completely incompatible signal driving waveforms?
Do you know, that tablets (and most if not all digital devices with LCD screens) do not use a VGA signal inside? (You know, VGA is an analogue signal and there is no point to convert from digital to analog and then do the same backwards in the LCD?)
More than likely you will find there a DPI interface (RGB parallel data + Vsync, Hsync, DE and CLK) or a serialized form of that video interface like DSI or LVDS?
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You should probably study first to know what are you diving into, rather then quickly slapping together ideas, while not having any clues of how those work.
hey? relax.
Do you know what a refresh rate of eInk is? How their service life is affected by the number of refreshes?
Yes, not directly compatible with anything like CRT and Screen, so what? I saw a prototype of a device which accepts VGA 640x480 pixel refreshed at 60Hz signals, samples into a video ram, and uses the video ram to randomly update the eInc screen on differences. Weird, but interesting.
Do you know what a VGA signal is? How to convert it to digital? How to put the digitized VGA in the eInk display, which will more than likely have a completely incompatible signal driving waveforms?
Do you know, that tablets (and most if not all digital devices with LCD screens) do not use a VGA signal inside? (You know, VGA is an analogue signal and there is no point to convert from digital to analog and then do the same backwards in the LCD?)
More than likely you will find there a DPI interface (RGB parallel data + Vsync, Hsync, DE and CLK) or a serialized form of that video interface like DSI or LVDS?
I know what VGA is. I have already implemented a couple of VDU devices for FPGA; the weirdest and funniest comes with serial RS232 input that produces VGA output, kind of hardware vt100. Recently I have also developed adapters to convert VGA signal input into LVDS output for LCDs (I know, there are also Chinese products like this). Analog to digital is not a problem, no doubt it's not a design that one would do, but, on some workstations, you don't have any choice since you don't have any modern stuff.
I would for sure use a modern graphics tablet with a built-in LCD if the machine had a USB input for the tablet and a DVI/link-display-something device output. Unfortunately, it has none.
edit:
Anyway, the title of this topic has been changed: rethinking about it, eInc display adds too cost and complexity. I'd better stay on an LCD screen, but I still need something that has no metal or components on the back of the glass otherwise it would interfere with the magnetic field of the Wacom's circuit.
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Not 100% sure I got exactly how you want to set this up.
Are you thinking of putting an LCD panel directly on top of the Wacom tablet, use the "pen" on the LCD surface and expect the LCD not to interfere with the tablet's normal operation in any way? Or how would this be mounted and operated?
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Are you thinking of putting an LCD panel directly on top of the Wacom tablet, use the "pen" on the LCD surface and expect the LCD not to interfere with the tablet's normal operation in any way?
yes, precisely.
On DTB we have recently done some tests. It might work, but the sensor on the Wacom tablet starts to have troubles if the pen is more than 9mm far from the sensor. We used thin surfaces of polycarbonate, 1mm thickness each, we progressively stacked, and tested on which substrate the pen starts to have bad behavior. The 9th layer was the last one tolerated, thus 9mm is the maximal spec.
I guess glass + liquid crystals do not interfere, but metal objects for sure do: it still needs more tests.
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how would this be mounted and operated?
we'd like to rebuild the final device in a way it can be used attached to an LCD mounting arm. So the arm will be attached to our woody desk, the screen updated by VGA signal, and the pen read by a serial RS232 line.
Drivers (the software side) is not a problem, we have already written something that allows GIMP to operate.
On the other hands, supporting USB-HID graphic tablets seems a bloody hell from both the hardware and software points of view :palm:
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If I were you I would consider some computer vision based approach. Probably much simpler.
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There are many modern LCD panels that embed LED backlight and are just a couple mm thick, in all kinds of resolutions and size. Most of them are either LVDS or eDP, and controller boards with VGA inputs are easily available. I think some don't have a metallic back, although there's almost always at least a metallic frame around them, so you may lose at least some margin, if that doesn't cause more severe issues to the tablet's sensing. You may be able to carefully remove the frame though...
Example: http://www.ebay.com/itm/HDMI-VGA-2AV-Remote-LCD-Controller-Board-7-1280x800-N070ICG-LD1-IPS-LCD/181145243253 (http://www.ebay.com/itm/HDMI-VGA-2AV-Remote-LCD-Controller-Board-7-1280x800-N070ICG-LD1-IPS-LCD/181145243253)
But I would expect them to emit enough EMI to cause major issues with a graphic tablet stacked just beneath them. They are not very expensive though, so that may be worth a try.
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That said, using an LCD panel with a capacitive touch panel overlay seems a lot simpler. You can find them either pre-assembled or as spare parts at AliExpress for instance for very reasonable prices. Some of the touch panel overlays come with an USB HID controller and are easy to interface with most OSs. Don't know if that would fit your needs.
On the other hands, supporting USB-HID graphic tablets seems a bloody hell from both the hardware and software points of view :palm:
Well, I don't know what kind of hardware and OS you're going to use this on...
I've recently bought a touch panel overlay (13.3") to mount over an IPS LCD panel that I already had laying around. Tested it and it works fine. Now I have to mount that in a custom frame.
https://www.aliexpress.com/item/For-13-3inch-323-195mm-multi-touch-G-G-Digitizer-Touch-Screen-Panel-Capacitive-Sensor-USB/32958246370.html (https://www.aliexpress.com/item/For-13-3inch-323-195mm-multi-touch-G-G-Digitizer-Touch-Screen-Panel-Capacitive-Sensor-USB/32958246370.html)
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I guess glass + liquid crystals do not interfere, but metal objects for sure do: it still needs more tests.
Well, even if you have no metal you do have conductive paths in the glass. Also, modern LCD's have the driver IC's mounted on flex PCB's inside the unit, so whilst the back may just be plastic, there will be "metal" between the back cover and glass around the edge.
It seems you're just assuming that an LCD, along with all its driver electronics switching at kHz and MHz frequencies, won't interfere with capacitive sensing behind the display. Whilst the backlight lightguide, and glass itself may not interfere too much (even though the glass is essentially a grid of conductive lines) I'll bet the drivers will. And if the backlight is PWM driven, the integrated LED's could too.
It is fairly easy to test - first try it just with LCD glass over the top of the tablet, no drivers, no connectors, no backlight. Then with the backlight, then with an LCD begin driven. As you've done display drivers for FPGAs before, I'm sure you could pick up a cheap monochrome 320x240 STN display for <$10 to play with.
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I also wonder how modern graphics tablets are built.
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Well a quick google came up with this: https://hackaday.com/2014/06/08/converting-the-wacom-intuos-into-a-cintiq/
Looks like they do just strip down an LCD display and use that, although I'm willing to bet there are caveats.
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The display [Bumhee] used for this modification is a Retina display from an iPad. With the right adapter, you can easily connect one of these displays to a computer, giving you a very thin 2048×1536 9.7″ display. The initial tests to see if this mod would work on his tablet – removing the metal shield on the display, placing it on the tablet, and drawing – were a success, giving [Bumhee] the confidence to irreparably modify his tablet
iPad retina. Bah ...
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I don't think you have to use that exact display.... I linked it as a proof of concept
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the questions for this tipis are -a- does it make sense? can it be done? -b- which display is the more appropriate for the purpose?
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maybe you can look at a lenovo X201 tablet display
than one has capacitive touch + LCD with CCFL backlight + wacom tablet.
also, i've seen an old HP "tough-book" with the same construction
i think you can find a part number for the lenovo LCD, and a decent datasheet
the tablet and touch screen part connects via USB
i think this is the part:
https://static1.1.sqspcdn.com/static/f/489821/26342342/1435254504897/HV121WX4-120.pdf?token=eehWjUDTMAuBqM7VSrFvppTsYaA%3D (https://static1.1.sqspcdn.com/static/f/489821/26342342/1435254504897/HV121WX4-120.pdf?token=eehWjUDTMAuBqM7VSrFvppTsYaA%3D)