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Book Scanner 2: Basic design elements...

After some careful consideration, I’ve decided to just go ahead and start building something. I’ve got most of the stuff around, so If I have a serious change of heart, I’ll toss it and start over. After finding a couple of clamp lamps left over from a precious model railroading project that I abandoned, It turns out that the only items I really needed to source were the cameras, a couple of SDHC cards, the trigger mechanism, and some glass or acrylic for the platen. I’m pretty sure that the remaining parts, which are mainly wood scraps, are floating around my shop somewhere. After discovering that the favored camera, the Canon Powershot 590, is no longer available in a practical way, I found that some folks have had good luck with the Canon Powershot A480. I found this camera refurbished for under $70.00 (at that price, two of them cost less than any single camera I currently own), so i grabbed a couple of them. They showed up today, and turned out to be pretty much exactly what I expected, so I am happy!

The DIY scanning community tends to fall into a few camps as far as how to control the cameras. The Book Liberator uses the most basic of methods: pushing the button to take a picture. It doesn’t get any simpler than that, but I think it does get better. It sure seems to me like it would be awfully easy to move the camera around, probably imperceptibly, but I’d be willing to bet you’d see the blurring in the full-size scan.

Some people have used Gphoto2 , a nice, open source digital camera interface. This is actually the method I’d probably most like to use. In theory, one could use this method to bypass the need for a card at all. You could just check the shot on your monitor, then capture the image directly to your hard disk. Nice! Problem is, the a480 doesn’t support that kind of remote viewing, so it’s not an option.

The most common method for image capture is to use a version of the Canon Hack Development Kit (CHDK). This is a wonderful project, in the finest tradition of open source community software. CHDK replaces the firmware in a number of Canon cameras, and allows certain features to be implemented which were not part of the original specification. The big feature for DIY bookscanner builders is the ability to trigger the camera remotely through a USB switch. Most builders place this switch somewhere on the chassis of the scanner, and a quick click gets both cameras to fire. There is an offshoot of the CHDK project that is near and dear to the Bookscanning community, and that is StereoDataMaker (SDM). This project was originally intended to make it easier to create stereo images with multiple cameras. Well, guess what, most bookscanners are using two cameras! SDM is also much more lightweight than CHDK, and covers all the bases the scanner community really needs. A small bummer is that the installer for SDM is Windows-based, and there aren’t really any clear descriptions of how to get SDM working manually. Someone was skilled and good enough to create an installer for the Mac, and the gneral tone of the advice out there is to use one of the installers, even if you have to go find a Windows machine. It doesn’t really matter, of course, since the firmware is just being copied onto an SDHC card, so the exposure to Windows is thankfully brief. Of course, I’d still rather do the whole thing from Linux, but what the heck…

I ended up going the SDM route. Despite having to go into my seldom-used Windows 7 boot (only for a minute, the installer is really small and fast!), the install went smoothly, and I was able to successfully trigger my cameras by unplugging and then re-plugging the USB cables, so I know that the only feature I really need will be working just fine.

My daughter and I had some time to kill today, so bribed her with hot chocolate, and we walked from Starbuck’s to the hardware store (across the street) to look for some glass. The consensus seems to be that “Doublestrength” glass is the way to go. I was figuring on seeing what sizes were more or less “standard”, and sizing my platen appropriately. I own a glass cutter, but my previous cutting experiences told me not to even try on any piece of glass that I actually paid for. Anyway, the store had a scrap of doublestrength at 12″ x 30″. The guy was nice enough to cut it down the middle, so I ended up with two nice sheets, 12″ x 15″. I figure that will be sufficiently large to scan over 95% of the books I could ever want to scan.

Cameras and Platen Glass

Cameras (Canon a480s) and Platen Glass (2 sheets, 12"x15").

So a couple of the design points have been determined: I will be using 2 10 megapixel cameras, loaded with SDM. The platen will be roughly 12″ x 15″, with an effective scanning area of somewhere around 11.5″ x 14.5″. That seems to me to be most of the important decisions for the time being. I’m actually hoping that I can get most of this thing built in a solid day in the shop, but I’m pretty sure I’ll then be spending several weeks getting everything tweaked and set so it’s just right.

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