just grab an lm7805 from your local hacker store and wire it up. connect the positive battery terminal to the 7805 input pin, the positive usb pin to the 7805 output pin, and connect the ...

You know just what to do. The ground pin of a LM7805 connects to the cathode of a TL431 programmable Zener diode pulled from an old scrapped TV. The diode is referenced to a voltage divider ...