Well, I've been absent for a while because I'm moving and having some serious health problems. But I haven't abandoned my mission; far from it. This weekend I got some help from Wolfgang Teder, a brilliant neuroscientist/EEG expert that I'm friends with. I built the base of the first book scanner in his workshop. He helped me design a high-current intermittent LED lighting system for the portable book scanner.
System description video showing the LEDs kicking ass:
YouTube video should be here shortly:http://www.youtube.com/watch?v=cSWj0c6j5P8
Higher quality Vimeo video will be here, but it will be a while:http://vimeo.com/user1097911
A transformer drops 120VAC to ~36VAC. A bridge rectifier and capacitor complete a basic linear power supply. The positive output of the supply is connected to a series array of Cree Q5 LEDs. These are connected to the drain of a high-power MOSFET MTW14N50E. The drain is also connected to ground through a 470 ohm resistor. This resistor serves to keep the LEDs on constantly at a low level. The source of the MOSFET is connected to ground, and the gate switches the whole thing on when fed 2-5VDC. This input also has a small pulldown resistor to keep it off when nothing is connected, and a Zener diode to prevent overvoltage. Very robust. In this iteration, the 5V input is from a voltage dividing tap across the power supply, made from a couple resistors. In the final circuit, it is likely that I will drive it with Arduino.
Things I learned:
How to switch with FETs (well, a little anyway).
Not to use the current-regulating drivers from DX (they weren't driving the LEDs anywhere near hard enough; pointless things).
How to fuck up a dead simple circuit, and recover.
Good soldering irons (Weller, Hakko) are totally worth it.
How to calculate the necessary transformer size for a given application and throw together a mean linear supply.
Relevant electronics principles being explained to me by Wolfgang: