This is my entry for the flashlight contest.
In this instructable I will be showing how to make a rechargeable flashlight that charges from your car. I got this idea as I often find myself using the flashlight that I keep in my car, but have come to it many of times with a dead battery. So my idea for a rechargeable flashlight started. It is fairly simple device, it is a flashlight after all. I did need to order one part from the internet. The light output of this flashlight is quite usable and probably perfect for being used around a car. With that said let's get started making the flashlight.
Step 1: Parts and Tools
Just a quick breakdown of things I used in the process of making my light.
3 white leds
5 10 ohm resistors
small switch ( I used RS # 275-0645)
li-ion or li-poly battery (single cell) (mine is only 70mAh)
li-ion/li-poly charger single cell ( I got mine from adafruit here, sparkfun also makes one)
USB mini B connector (cut mine off a usb cable)
power connectors for the board and battery (see picture)
power adapter/plug ( I used RS # 274-1569)
power jack (RS # 274-1577)
I used some plexiglass I had laying around
And finally for my housing an Altoids can
Solder Iron and solder
Helping hands (sure are helpful)
light (helps to be able to see what is going on)
Dremel with various bits (hacksaw and or tin snips can be used instead)
drill and drill bits
Sharp knife (always useful at some point)
Well hope I did not forget anything :)
Step 2: Making the LED Array
The first step is to figure out how to arrange the LEDs. Since my power source is a Li-Poly battery which gives out 3.7V I could not arrange the LEDs in series. So I used parallel. To correctly use LEDs you must use a resistor on the negative leg of the LED (this is the short leg or the side of the LED with a cut to it). In parallel you should also use a resistor per LED and in my case that means 3 resistors. To make it easy to solder the resistor and LED together I hooked them together as seen in the first picture. I then soldered, and snipped away the excess material. Once I had done this for all 3 of my LEDS I soldered them together. I started with the positive legs and soldered together as seen in picture 2 below. I did a similar thing with the negative legs (now with resistors) as seen in picture 3 below. Picture 4 below shows a switch wired to the positive legs, and finally all attached to a power connector for the board.
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.
Step 4: Assembly
So finally came time for shoving the components into a box. I choose a Altoids can as well, they are awesome. First I drilled out the holes for the LEDs, the switch and the charging plug. Then I used my dremel to cut a hole on the top so I could view the status of the battery. Then using some superglue and electrical tape I put it all together. Basically I needed to figure out what configuration would work the best for my enclosure and then adapt it.
Step 5: Let There Be Light!
So I charged my light a bit then tested it. Light output seems pretty decent. Good for most applications I would say.
Some final thoughts;
I would like to figure out a better solution for converting the 12v of the car to 5v or 6v required by the charger.
Another thought that came to me after I had already made the light was to move the charger out of the light and into the car. This would allow for smaller enclosures for a better looking and feeling light.