In this design, the USB charging station can be unplugged when not in use. When charging the devices can be kept in your pocket or backpack.
The charging station has four AAA rechargeable batteries wired parallel to the female USB that provide a secondary energy storage and once charged can power a USB device independent from the bike.
You can use the dynamo to power the lights or the USB but not simultaneously. A toggle switch on the bullnose handlebars turns the front lights off.
Step 1: Circuits
LED for beginners: www.instructables.com/id/LEDs-for-Beginners/
try out different circuits... blinking, back light, combinations =>
As the front wheel turns it creates alternating current (AC) power. The 'bridge' is a rectifier that converts the AC dynamo power to DC power. The bridge is made up of qty(4) 1N5818 diodes.
Bike Light Encapsulated in Epoxy :
The battery pack absorbs any power not consumed by the USB device.
qty(4) 1N5818 Diodes
qty(8) White LEDs
qty(1) Battery Pack
Step 2: USB Charging Station
First I wired the battery pack and USB devices in parallel.
Next I partially disassembled the battery pack and wired the phone jack. I arbitrarily used the Left channel of the phone jack as DC positive. You just have to be consistent when you work on the handlebar connection.
I drilled a 1/4" hole in the lid for the 1/8" jack to stick through.
Step 3: LEDs
I assumed these LEDs used normal voltage (~3 volts) and this was confirmed by looking at the Cateye circuit that has 2 type N 1.5 volt batteries in series powering qty(3) LED lights in parallel.
I have a 6 volt dynamo so I just wired both sets of 3-volt cateye's in series to equal 6-volt. Typically it is recommended to use resistors if you have more voltage than allowed by the LED. They work great so far in series so I'll let everyone know if the LEDs fail seemingly premature.
12/1/09 update => So the LEDs burnt out... :(. ... so I bought qty(8) LEDs and used a similar parallel configuration. This time I used ONE 40ohm resistor.
Why did the original cateye's burnout? I found the dynamo was creating a lot more than 6 volts. For instance, the new circuit achieved a total voltage drop of 14 volts!
A bench test shows the NEW voltage drop across each bank or LEDs is ~3.4 volts (within specs) and the voltage across the resistor is 7.5 volts.
Another layer of circuit protection would be a dedicated resistor for each LED so I'll let you'all know if this circuit fails or lasts.....
2/09/10 Update: Sooooo the problem with only using qty(1) resistor is you are dissipating a lot of wattage through this 1 resistor; that is,
7.5 volts / 40 ohms = 187 mA. (through the resistor)
VxA=watts so 7.5 x 0.187amps=1.4 watts.
You are not going to find a 40 ohm resistor rated at 1.4 watts. So in lieu of this (and after burning out a lot of resistors) I used a 100 OHM 1/2watt 5% carbon Film resistor.
This should bring the amperage through the LEDs down to the 20mA specs for normal LEDs. You can certainly buy LEDs that allow higher currents (80mA, 90mA, 250mA, 300mA, and up) but these require a little bit more care (heat sinks!) to dissipate the heat. Pilom uses a 5mm thick piece of aluminum to transfer heat away from the LEDs.... check it out.
11/30/2010 Worked great for over a year! check this next iteration out==> shortly.
Step 4: Handlebar Work
11/30/2010 - yea that dinky switch worked for about ~2 months of oregon rain... (piece of !>#()
any ideas for a good waterproof switch?
I got the little PCB kit from Radio Shack for ~$2. It's similar to the one listed below. I had to cut the board down to size to fit it into the handlebars. I used hot glue to protect the PCB and diodes. (thank Jay for the idea). http://www.radioshack.com/product/index.jsp?productId=3173937
The qty(4) diodes 1N5818 can be found here for $0.38 each:
All the parts 'n pieces get inserted into the handlebars. Wrapped some of the wires under the handlebar tape (see pic).
Filled up the holes with a glue gun for weather protection.