@daniel: There's been no issues with the PSU this far, though it's also true that apart from testing I've scanned only one book with it. But I don't see any reason as to why it should fail once it's working. I bought two PSUs from the local recycling centre 6€ apiece, I thought I'll modify the other one into a general purpose "bench PSU" for electronics projects, but found one of them wasn't working; apparently there was a fried component (judging by the black dirt around some diodes), but I didn't investigate it further.
Page turning with the foldable platen works so that after taking a shot I fold the platen (turn the right side on the left), lift it with one hand and turn the page with the other. Then I put it back on the book. The main reason I did it like this is that lifting a fixed-angle platen would have required that I put the cameras more apart so that there's enough room to lift the fixed platen without having to worry about it hitting the cameras.
Possible downsides are perhaps that with small books the 20cm x 30cm platen tends to rise a bit in the middle, so that you have to hold it lightly in place by hand. I haven't found that too inconvenient though, because you only need one hand to operate the trigger, so the other is free to do whatever in any case.
I scanned the first book with it yesterday, 200 pages took 15 minutes, I'm pretty happy with the rate. The book itself BTW was printed in fraktur, but running it through Tesseract 3 + VietOCR with German Fraktur as the language setting produced relatively good results (not significantly worse than the usual OCR output for Finnish).
@jancoj: I modified the PSU as per the instructions here:
http://web2.murraystate.edu/andy.batts/ ... SUPPLY.HTM
The modification process is relatively simple (then again I'm an electrician), because the PSU supplies the needed voltages (3,3VDC and 5VDC) out of the box. Basically you just have to connect a 10W / 10 Ohm resistor between one of the 5VDC-GND wire pairs, and connect the POWER-OK wire to another GND wire. Normally POWER-OK is connected to GND through its being connected to the motherboard, so in this case it has to be fooled into thinking it's connected to it. (What the different color wires were was written on the side of the PSU). The modification instructions said that the PSU needs the 10 Ohm dummy load in order to work. I didn't try whether it really needs it - the resistor was only 1€, so I didn't see a point getting possible trouble by trying to save the money, and no doubt the original author of the instruction was better informed as to the functioning of a PC PSU than I am.
I lowered the 5VDC with a diode which lowers the voltage 0,6V (but does nothing else in this setting), because the CHDK wiki emphasised that the USB trigger pulse should be no more than 5VDC (
http://chdk.wikia.com/wiki/USB_Remote_Cable).. the actual voltage put out by the PSU was 5,2VDC or something, so even though in practice it might have made no difference, I decided to play it safe as the trick is relatively simple, because the wiki did say (
http://chdk.wikia.com/wiki/CameraFeatures) the needed pulse is somewhere between 3,5 and 4,5 VDC.
For powering the cameras I used the 3,3VDC without modification (or regulation), even though the nominal is 3,15 VDC.. I judged that was within tolerance. Maybe digital cameras are more refined electronics-wise, but in my general experience electronics work with voltages that can deviate a lot from what the nominal voltage is (see e.g.
http://hackaday.com/2012/01/04/exposing ... ue-prices/, which actually deals with digital cameras.. the "DC" at 2:16 - what a load of rubbish! :'-D ). Most probably the 3,15VDC nominal is there because Class I DC plugs have 3,15 VDC nominal maximum.
I haven't measured how much current the cameras draw from the PSU, maybe I could do that at some point.
