Fiddly B1ts

Adventures in Over Engineering

by on Jun.11, 2012, under Multitouch

So, we have four cameras stitched but to get all 16 routed into this poor little PC, I plan to use a four terminal USB 3.0 PCI-E card and four hubs to concentrate each of the four cameras down. Well that is a lot of cabling, so much so that it will basically yank the PCI-E card right out of the mother board. So yet another step in this little journey was to provide some security to the expansion cards. It was going to happen sooner or later and the video card was fairly secure so there was no rush until now. I had some 1/2” x 3/4aluminum angle lying around from another failed experiment which served nicely. Making use of almost all of my clamps and the handy project table I got for Christmas, I managed to bolt something together. The cards, they are not going anywhere. Now, I await the arrival of another USB 3.0 card as I’m pretty sure the one I have now is fried. Too many unintended exits from the motherboard while I ran cables.

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Finally, some touches.

by on Jun.05, 2012, under Multitouch

Ok, so finally we got some touches stitched together last night. You can see here the dual 1080p desktop with the four quadrants represented in the grid. This is really used to make sure that the touches are falling within acceptable boundaries for each camera from the perspective of the projected image. Granted, it this final test it is just the lower left quadrant ( under CCV ) but its the last bit I wanted to see work before I buy 12 more camera kits. Overlap is quite good across camera boundaries and the hand-off from one camera to the other is smooth. It would have been nice to have all of the cameras fitted with 850nm filters for the test but it was not worth the delay. I think this scheme will do well enough.

In this layout, the upper right camera is actually imaging the mirror and the other three are pointing directly at the acrylic. Working this out took quite a bit of trial and error with lens swapping and moving cameras around in a fairly cramped space. The mirror for the TV is not helpfully placed in the slightest. So I will order 3 more sets of lens kits and replicate this for the other three quadrants. And then, hopefully, the PC won’t collapse under the weight of 16 cameras crushing those four little cores…

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What exactly is going on?

by on May.31, 2012, under Multitouch

Table ready to go for a remote game weekendOk, so no posts in about 6 Months. Not what I would call a good track record for the blogging. So what has been going on? For one, there have been some cosmetic changes, and the second thing is a ton of work fussing about with cameras. But first, it is important to note that the table has proven (semi) portable! I had a sheet of 5mm plywood cut to fit the top of the table and used cargo straps to hold that in place. We took the legs off and stuffed the whole thing into a mattress bag as rain was of course inevitable. That went into the back of my truck and me and the boys drove it up to DC from our home here in NC for gamage. I’d say things went delightfully. Setup was about 10 minutes worth of work and all was well. To be honest it is a beast and requires a couple of guys to properly wrestle but I’d say its worth it. I think a trailer might be a good choice next time…

Right, so for the cosmetic stuff. I added grill work on the end-caps of the table to provide venting for the TVs. The end-caps were buckling due to heat build up which clearly needed somewhere to go. I managed to source a sheet of perforated steel from Amazon ( what can’t be bought on Amazon these days? ) and took the trusty Dremel to it. I cut out 3 3″ holes in each end cap and then cut out corresponding grills with 1/4” tabs to hold them in place. After that I hit them with self-etching primer, which I have to say sounds rather terrifying, and then some black automotive paint. All in all I’d say the effect was pretty worthwhile. The only hang up was spending an hour or so with the grinding wheel on the Dremel touching up the edges to get them to fit as seamlessly as possible. Its the little details that make it look clean.

So on to the more important topic of where the hells are the touches? Quite a bit of time has already been spent trying to get an imaging plan for the table that will actually work. 4 Cameras, while economical ended in tears for several reasons. The light contribution from the edges of the image was way too weak to be detectable. The angle at which the light was entering the camera from touches at the edge of the image was too oblique and there were just not enough photons. The other issue is that I needed a 1.7mm focal length lens which just meant that way too few pixels were dedicated per square inch of the table so a 4 pixel touch was not quite easy to detect unless it was very bright. So given all that, the next step was to subdivide each quadrant of the table. Moving to 8 cameras still meant that one dimension was going to require a very high FOV, so 16 cameras it is. To test the theory I ordered a lens pack from Peau Productions to find good fits for the sub-quadrants. I ran twine across the quadrant to give me a target for the cameras and then started swapping lenses and fiddling with the cameras until I managed good placement with no shadows and a tight imaging of the sub-quadrant. Now given that there is a very large mirror taking up most of the space in the TVs there isn’t 850nm Filter much room for cameras. Also there are 4 sub-quadrants in the center of the table that need imaging. The solution to this was to position cameras along the edge of the table and image the mirror itself in order to grab those touches. This gives me a much longer focal length to work with as well as keeps the cameras out of the way, as you can see in the alignment grid picture. Some extra work will need done to flip the image properly but that is a small matter of software. So I have the four camera positions, appropriate lenses780nm Filter Test and a reasonable mounting system worked out. The one last thing I wanted to test was filters as I had initially used 780nm filters at work for the larger sized table but was concerned that too much arbitrary light was getting into the camera and washing out the touches. This turned out to be the case. After a trial run with a 850nm filter we are getting better contrast for the touches and good response. So finally I want to run one more test to get the 4 cameras of the table quadrant stitched just to be certain that all will play nice and then its time to put in a big order for the other 12 lens kits. I managed to score a nice pile of PS3 Eye cameras on ebay for a decent price so we should be pretty close to making this thing work.

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