This instructable shows how it's possible to make one 5V usb charger from an old 9V battery, useful to charge cellphone's batterys.
The charger in the picture it's already working - it already charged my cellphone last night. But it still needs to be closed inside some case, that should be the 9v battery case kept from it's disassembling process.
However, here goes the instructions, with the electronic scheme included...
Step 1: Materials
The picture shows the components needed to assemble the charger, including one empty case from an old toothpaste, that can be useful to put the charger inside in the future, in an updated step...
And the list of components and materials is:
1 old 9v battery
1 USB port type A (female)
1 Regulator 7805
1 green LED
3 resistors 220R
1 empty case (optional)
Step 2: Schematic
In the computer, using any electronic circuit maker, can be made one scheme like the one in the picture, where I've added a diagram of the pinout of the regulator 7805 and of the USB port.
Step 3: Solder the Components
After the disassemble the old battery, the base with the connectors it's useful to solder the components on, starting with the Ground pin of 7805 (pin 2), soldering it directly to the negative pole.
Pins 1 and 3 must be softly lifted up, in order to solder the other components, according with the scheme of the previous step.
One resistor is connectd in the positive pole with a minor size than the base, in order to connect to the Anode of the LED, making a series from the positive 9V pole to Pin 1 of the Regulator.
Pin 3 of the regulator (output 5V) is then connected directly to pin 1 of the USB port, soldering a wire.
The Data pins of the USB connector are connected with 2 pull-up resistors to the pin 3 of the regulator
To finish, pin 4 of the USB port it's connected with a wire to the negative pole of the battery, where it's already connected pin 2 of the regulator.
The result must be like shows the picture, where we can see the charger charging the battery of my mobile and we can read in portuguese: "Bateria está sendo carregada" - Battery is being charged... ;)
Step 4: Final Product
And the final product must be like it's shown in the picture! Now I have one mini-charger, handy to have in the pocket with a battery, for the urgencies. ;)