technology from back to front

A touchscreen mod for the Asus Eee 701

Tony and I bought Asus Eee PCs a couple of months ago, largely to experiment with. He’s been using his quite a bit, and had some fun installing Ubuntu. Mine has been languishing at home, waiting for its tooth on the cog to come around.

Recently, someone pointed me at a YouTube video of unrepentant modder jkkmobile fitting a touchscreen to his Eee PC. The cog turned, and I ordered a specialised touchscreen overlay kit from eBay they are quite easy to find.

There’s four bits to the kit: the touchscreen itself, which has a ribbon; a touchscreen controller PCB; and two cables, one from the ribbon to the PCB, and one from the PCB to USB. Some kits (like the one I bought) purport to be solderless; however, the cable meant to connect PCB to USB ended in the familiar A type plug, and had a choke (which we had a bit of fun destroying).

The overlay is a 4 wire resistive touchscreen panel, meaning that it works with a finger, a (capped) pen, a PDA stylus, or whatever. One just has to be careful not to use anything sharp or inky.

The first task was to take it all apart and determine where and how to accommodate the controller. Taking it apart consists mostly of two activities: unscrewing screws and popping the various clips in the case. A fiddly bit is taking the keyboard connector out, which requires especial delicacy because the housing is quite sticky and its easy to scratch the ribbon – this goes for the touchpad connector too.

As jkkmobile mentions, there’s a bit of space here and there for the controller. I didn’t want to sacrifice a speaker, as he did, and I wasn’t planning to do any more modding, so we used the space-of-least-effort, which is beside the memory housing on the underneath of the motherboard. We used a bit of insulation tape to separate the board from the motherboard; it took a few layers, since the pins on the underside wanted to poke through, and we had to trim the plug casings (other people have removed them altogether and soldered the cables on).

With the controller board in roughly the right place and cables plugged in, we routed the wires up through the gap between the motherboard and the case. It’s probably worth wrapping some tape around, so the edges don’t strip the sheath away.

The next choice was what to connect the USB endpoint to. USB cabling consists of four (sometimes five) wires: two for data, one (or two) earth, and one +5V power. On this, jkkmobile says that an external port would be fine except for the power lead, which ought to be connected to a power source that turns off when the PC does. I was happy to sacrifice one of the three external USB ports, so the earth, D+, and D- went to the pins of the lonesome port on the left-hand side of the case. tnkgirl helpfully provides a guide to the various USB traces on the motherboard, from which we choose a seeming spare (and verified its behaviour with a multimeter). We also had to check which colour wire corresponded to which pin, again with the multimeter this is left to vendors in the USB specification, though there is a convention.

Then there was soldering. At this stage I would like to point out that the last time either of Tony and I abused a soldering iron was under heavy supervision when we were about twelve. Nonetheless, we were game, and a couple of hours, countless Watts and a burnt finger bought us some shiny conductive solders. We ended up using some conducting epoxy to glue the earth to the port shielding, but it could equally (health and safety concerns aside) have been soldered to the pin.

The penultimate task was to attach the touchscreen and plug it in. I used double-sided tape along each edge of the LCD display. I left the backing on while I cleaned the screen one last time, then lined up the panel and pressed it on, with the ribbon at the bottom where there’s a bit of room out of the way of the camera. The panel overlapped the LCD by about 5mm at the left edge, so I had to trim the plastic clip on the fascia and cope with there being a bit of a bulge on that side.

The cable from the controller to the screen had to go from the keyboard part of the case to the screen part of the case, so I routed it through the hinge along with the camera and left-speaker wires. It took some persuasion, but there’s actually plenty of room to spare, both through the hinge and over the motherboard (the mic and speaker plug housings rise a good few mm above the board, for example) certainly enough for the cable to go through a couple of 90° bends. The ribbon from the panel is robust enough to be folded too, though perhaps don’t score it first.

While putting it all back together, we had a heart-stopping moment as it started refusing to boot past the initial firmware. At first we thought it might be the keyboard, and in particular the keyboard connector ribbon. In general these are often very sensitive, and known to be so, for the Eee. However, we are nothing if not scientific here at LShift, and we’d soon discovered that it was not the keyboard, but in fact some other problem that disappears when the motherboard is prodded in a certain way. After defouling some wiring and cycling its state of assembly, it booted consistently again.

Last came the software. The Xandros distribution happily recognises the USB controller, loads the usbtouchscreen module, and treats it as a mouse. However, it needs calibration, so it ends up being an insane teleporting mouse. A fair amount of interaction with Google led us to believe that the answer was to treat it as a different input device; that is, stop it looking like a mouse, and have a special input driver for it.

What normally happens is that it gets assigned something like /dev/mouse1, which is interleaved into /dev/input/mice, to which the X Window pointer input driver listens. To stop it looking like a mouse, it’s necessary to have a specific rule for it in /etc/udev/rules.d/:

KERNEL=="event*", SUBSYSTEM=="input", SYSFS{idVendor}=="0eef", SYSFS{idProduct}=="0001", SYMLINK+="input/evtouch_event"

(The values for idVendor and idProduct come from examining cat /proc/bus/usb/devices)

I compiled a specialised X input driver for it – to do that, I had to install gcc, and to do that I had to add repositories to /etc/apt/sources.list – and configured it as an input device.

To calibrate it, Tony wrote a tiny program to interpret the numbers from the event stream:

import sys
for line in sys.stdin.readlines():
  (d3, d4, d1, d2) = line[:4]
  hex = d1+d2+d3+d4
  print int(hex, 16)

and a few pipes and filters later we had our min and max values:

xxd /dev/input/evtouch_event | grep '0300 0000' | cut -d' ' -f8 | python byteswap.py | sort -n

(byteswap.py is the file with the Python from above. The ’0300 0100′ filters for the event type and the X axis; the Y axis is ’0300 0100′. I’ve doctored the original line used to be a bit simpler, so it may need some hacking).

I needed a bit of experimentation with the XSwap, YSwap and Rotate options in the input driver configuration in xorg.conf, with accompanying restarts of X, then it was done!

The resolution is such that it’s possible, with a bit of concentration, to browse web sites with a finger. A nice side-effect of the screen layout is that it’s possible to scroll a full-screen window by running a thumb along beside the bezel.

by
mikeb
on
15/05/08
  1. John O'Hara
    on 16/05/08 at 12:50 pm

    Wow!
    Practical and cool.

    Every EEE PC should have one!

    Do you know if you can get this component for the “new EEE” sized screen?

    John

  2. Hi John,

    I did a quick survey of the googleweb, and didn’t see much sign of 8.9″ resistive touch panels. There were rumours that the 900 would have a touch screen, of course, so presumably someone somewhere makes them.

    Now the 900 is in stores, the mod kit cottage industry will no doubt wind up.

    I think the higher (by £100 odd) price point of the 900 may discourage a few people — including me — from experimenting with modding. But well, I’ve done it once ..

  3. Hi! nice tutorial here. I was wondering if u could point me to the exact Store in Ebay where u bought it, heapz of them are selling and i dont knw which one is best. maybe u could give the seller name or store? or best exact link?
    I juz bought my asus and wanted to make it touch screen. thanks

  4. @Kaye: From memory, I really just bought the first one I saw that had the necessary components (viz a 7″ touchscreen overlay, controller, and cables with appropriate plugs).

    Having a quick look again, it seems that the ones advertised as being for the Asus Eee 7″ have the right components. They are all about the same price at £15-£20, too.

  5. I have 7 inch EEE touchscreen kits for sale for the old 701 models. I could even do the work for you, if your interested drop your questions in a mail to contact@piratelogic.nl

    cheers – cc

  6. It seems that some screens are thicker/ less durable than others. Alas after completing all the mods, and putting the fascia on over the screen the touchscreen cracked up. Even if it hadn’t, I’m not sure that the fascia would have fitted properly, and would probably have caused it not to close. So, the thinner the better…

  7. Incidentally, for driver installation on Xandros, following the guide at http://wiki.eeeuser.com/howto:kiddshoptouchscreenunderxandros worked just fine.

  8. Blackberry Playbook - Page 2
    on 30/09/10 at 8:07 am

    [...] to do this : A touchscreen mod for the Asus Eee 701 LShift Ltd. Learn the rules – so you know how to break them properly Simplicity is the ultimate form of [...]

 
 


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