This is the first in a series of posts recording the construction of DirtyGirl, our first attempt at a multitouch LCD screen built into my cheap-o IKEA Ramvik table. It’s going to be used as a total HTPC-A/V jukebox system. [This build log is meant for general computer fora with more mainstream users, so it goes in to a depth that many of you will find pedantic. Some of the explanations will be obvious to you.] So without further ado, fear my MSPaint skills:
The techniques applied here come from the vast http://www.nuigroup.com forums. Thanks to them [YOU!] for their tireless efforts in recording their pursuits. Nearly everything you need for this table is available from http://www.peauproductions.com. Nolan’s site is a store and educational resource that aggregates basic MT knowledge into one easy-to-follow (and purchase!) system. It’s actually the cheapest place I found to buy the multitouch goodies, and shipping was quick. He’s been of great help to me during this process, and continues to contribute to the NUI group as part of their forum. Without further ado, here’s the what makes DirtyGirl tick:
$199 - Acer 23” LCD Display (http://www.bestbuy.com/site/Acer+-+23"+Widescreen+Flat-Panel+LCD+Monitor+-+Black/9183224.p?id=1218049006792&skuId=9183224)
$260 - 2x PS3 Eye, M12 mount, 850nm filter, custom Peau enclosure ($130 each) http://peauproductions.com/store/index.php?main_page=product_info&cPath=1_6_10&products_id=15)
$30 - 2x 3.6mm lenses ($15 each) (http://peauproductions.com/store/index.php?main_page=product_info&cPath=4&products_id=28)
$116 - 4x 850nm lasers ($29 each) (http://peauproductions.com/store/index.php?main_page=product_info&cPath=16&products_id=38)
$12 - 4x line lenses ($3 each) (http://peauproductions.com/store/index.php?main_page=product_info&cPath=16&products_id=39)
$8 - First Surface Mirror sample (http://firstsurfacemirrors.com)
$625 Total Component Cost ($426 if you dismember your own LCD). Depending on your setup, you can definitely get away with three lasers and line lenses instead of four (I purchased one extra just in case) and one eye instead of two. You only need the first-surface mirrors if your setup requires you to reflect the lasers. These trade-offs will, of course, be dependent upon your setup and tolerance for inaccuracy in the touch events.
Now a bit about these components. First up, the victim. The IKEA Ramvik is a cheap, modern coffee table that Lady NYCEsquire has been trying to get me to replace. I’m doing her one better:
We chose the 23 inch Acer because it was cheap. $199 for 23 inches? Yes, please:
Unfortunately, you get what you pay for. It’s a low-grade TN panel, so the viewing angles are not impressive. This is a fairly critical point, since DirtyGirl will almost always be viewed from an angle while sitting on an adjacent couch. If we had mo dollaz we’d have picked up an IPS or equivalent panel that would remedy this issue. Still, the Acer has no “FFC” issues (see below), and this should make for an easy build. The stripped-naked LCD enclosure - nary a fig leaf:
(My little helper made it into the shot, as well). In some other panels, the Flat Flexible Cable connecting the LCD panel to the driver board is sometimes connected in such a way that it can’t be bent away from the back of the screen. The Acer takes a bit of wiggling to get apart, but is easy on the DIY front from there.
The PS3 Eye is a godsend to the multitouch hobbyist. It does 640x480 at 60 fps for fast finger-response times. It’s relatively cheap and well-documented compared to other webcams. We need two because the Ramvik is so short, we’re forced to place the LCD very close to the camera. Much of the LCD at this short distance would be outside the frame of a single Eye. This setup is pricier of course, but we didn’t have much of a choice, and it has the added benefit of tracking at double the resolution of a single camera. Here’s one of them stripped of the pesky OEM shell:
The PS3 Eye, like most webcams, includes a filter that blocks infrared light. Since we need to detect infrared light, these filters [chrisrock] have got ta go [/chrisrock] . Without it, the Eye is open to all visible and all infrared light. But this doesn’t end our modification. We need to block out all light, save one particular wavelength on the IR spectrum, so we install a bandpass filter at 850nm. This will, as the name suggests, allow only light at the 850nm wavelength to pass. Here’s a closeup:
Now that we’ve done this, we’ve screwed up the optics of the Eye pretty badly - to the point where the image is almost unusably blurry. The aftermarket M12 Mount and lens bring us back into focus, and restricted to the spectrum we want:
The peauproductions custom enclosure is precisely machined from onyx acrylic and fitted with a magnetic cover that snaps into place to protect the delicate Eye hardware. Muy sexy. Most importantly, it allows the easy switching of lenses and mounting vertically or horizontally on any surface and in either direction. It’ll save you a ton of frustration and is well worth the extra cash:
The lasers emit light at the 850nm wavelength. We chose 850nm over another, cheaper, 780nm version because it’s less likely to be affected by interactions from visible light. The included lenses focus the dot into a flat, razor thin beam:
They’ll be mounted under the table vertically, forming a verticle plane. What we need is a horizontal plane just over the glass top of the table, so we use a first-surface mirror at a 45 degree angle to reflect the beam. A regular mirror would give some refraction, sending errant IR into the camera.
That’s all for today. Next up:cutting and installation!