Rechargeable Flashlight for your Car

Step 3 Power cable and rough layout of the flashlight

Now it is time to figure out the power cable. According to Adafruit's page about the charger being used, it wants a 5v source such as from a USB port on a computer. Opening the spec sheet shows that the chip on the board can go up to 7v safely. The other thing we know is that a car runs on 12v DC power. Well 12v is much higher than 7v and is not safe. To fix this problem I am using a known trick with resistors called a voltage divider. If you look at picture 3 you can see how to assemble it. Basically there are 2 resistors in series connected to the car power. Then you simple tap the USB + wire(red) between the resistors and the - wire(black) to the - of the car. It is key that 2 of the same resistors are used. This will half the voltage, from 12v to 6v, which is safe for the charger.

The second picture shows all the parts connected to the board. It goes together so nicely.

If you are able to know would be a good time to test your voltage divider with a multi-meter. Plug the plug into a 12v source and look at the power coming to the pins of the USB plug (pins 1 and 5). You should see 6v, if you do good job, if you dont, make sure nothing is grounding out and your solder joints and connections are good.

Since I have assembled this I remembered about voltage regulators, could have used a 5v one... Anyways I would be most interested in anything that didnt consume alot of ghost power.