[DC/DC Converter]

what you'd need is smps step down design however this network
requires a control ic (most do these days) do a search with
the following keywords:smps stepdown circuit or smps stepdown
application notes,-- most semiconductor manufacturers will have this
information on their websites

[AAA Battery Charger]

you could make a simple one with a rectifier and resistor(s)

[LED]

audioguru:
Hi Bryen,
Welcome to our forum.
I've tried it. A LED makes a very inefficient photodetector. With an extremely bright light up close or light from a similar LED up close, they produce a little more than 1 volt with hardly any current. They also conduct hardly any current.
Why not use an efficient photo-transistor or photo-cell, that's what they are designed for.
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to overcome the insensitivity you could use a high-speed opamp
on the other hand yes youre right why not use what youvemention or infrared reciever,transmitter leds costing no more than a regular led