• Fix LRF
Front Light illumination
There are many different light sources available for illumination the screen of Sony Reader at dark. All of them are not perfect. The major imperfections are:
Modern technique for LED current stabilizers uses so called charge-pumps. In contrast to old-style parametric stabilizers, in which the excess of current is being dissipated on the transistor; the efficiency of charge-pump technique is close to 100% because there is no passive elements in the schematic. The chips for LED current charge-pump stabilizers are very inexpensive and requires only a few external elements.
2 LED Flex-Neck Clip-On Reading Light
Among many other lamps I tested, the 2 LED lamp with the flexible neck seems is one of the best illuminators. I made an improvement by replacing the two C2032 button batteries with 600 mAh Li-ion rechargeable battery (from Nintendo GameBoy console) and made current stabilizer based on the FAN5607 "LED Driver with Adaptive Charge Pump DC/DC Converter" by Fairchild. The chip costs ~2$ and available at www.DigiKey.com. It produces stable current through the LEDs within wide range of battery voltages, even deep discharge does not affect brightness of the LEDs.
The driver can support up to 4 LED, in our case we are using only 2 LED, the other 2 pins are simply go to nowhere. The current is regulated with the Rset resistor. The current for each of the LEDs vs RSet is shown at right. The capacitors must be ceramics (not electrolytic!) fast capacitors; I used capacitors taken from damaged hard drive ( they are brown color and have box shape). I built two similar units and used capacitors with unknown capacitance (just took the biggest ones) and both units work without any problems; so I think the capacitance is not that important. But take in to account, they must be fast (this is a key point of operating principles). The FAN5607 chip has current protection, so the chip can not be damaged with high current or even short circuit of the output pins.
The head of the lamp was cut with the knife (its glued and can not be separated by other way), the electronic schematic was inserted in the head together with Rset resistor (which replaces the on-off switch); the switch disk button is attached to the resistor and used as a wheel for current adjustment. The Li-ion battery is located in the box made (soldered) from PCB. The images are below, click them to get larger pictures.
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Update: Note, this project was done and published here almost a year before than Sony created similar, based on Light Wedge book cover. Now easier to purchase the illuminator from Sony.
LightWedge frontlight illuminators are deigned for regular paper books. They give nearly perfect illumination, but unfortunately, they do not fit the PRS-500, because big battery box does not allow to put the Wedge close to the screen. Besides, it requires 4 AAA batteries; that makes the LightWedge heavy. Current stabilization/adjustment is also missing.
To modify the LightWedge (PaperBack format) the following was done:
Here are the steps to modify the Wedge:
a) Disassemble the LightWedge and cut to fit the width of the Wedge to the Reader. Regular saw for metal or wood can be used. To make accurate cut and do not scratch the surface the direction of cut was along the surface.
b) Make a semi-hole symmetrically to the one we already have. Put 2 LEDs (original LightWedge's) to the holes and solder the wires. The ends of the wires goes through a hole drilled at the edge of the plastic wedge (for better fixing). 3 wires go out of the hole (see schematic diagram above). Cut LEDs legs as much as possible (I left ~0.5-1 mm), this is needed to reduce the size of the wedge.
c) Wrap the top of the wedge with a tape. Fill the volume with black epoxy to completely cover the LEDs and the wires.
d) Shape the epoxy with a file to make it smooth and rectangular.
e) Wrap the LED's area (at the level of white stripe) to prevent light coming out of the LEDs area. I used thin paper tape especially designed for optics (the tape is very nontransparent).
The box was soldered from the pieces of PCB cut with scissors. Preliminary, the bottom PCB was scratch to get pads for elements. The electronic schematic is the same to the discussed above. The FAN5607 chip is glued upside down to the PCB and connections are made with thin silvered wires inserted into plastic tubing. The capacitors are mounted (soldered) to the pads scratched on the board. The box includes adjustable resistor (100 k), the on-off switch and a connector to plug the cable from the wedge. The cover is attached with 2 screws.
The images of the box and the LightWedge are shown below.
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While using, the box is attached to the cover with U-shape steel-wire spring soldered to the box (see images). The LightWedge is attached to the Reader with 2 black ribbon bands. At dark the illumination is uniform, except small areas around the LEDs. The reading is very comfortable, none of the lamps give such quality of illumination. Also the LightWedge does not produce additional light and therefore does not bother the others. Here is the screen at dark: