Me and my wife have tried to used more renewable resources and cut down our use of electricity. The other day I noticed that my elliptical runs on it's own power. So then the next question was: "How much power is it generating?" Turns out it's about 8.8v when actively running, and goes down slowly from there after you stop. Then I remembered that there were many 9v to USB adapters out there, so I figured that 8.8v was probably close enough for it to work. Turns out anything above 7v works great.
I am not going to go over how to create the circuit itself, as there are many great instructables that do a great job. The following are links that I used in putting this together.
Portable USB Charger (Version 2.0)
Another Altoids iPod Charger
USB Adapter schematics
Another USB Grounding Dagram
Step 1: Test the Power
Step 2: Build Voltage Adapter
Take note that you will not need the 9v adapter, as we will be connecting directly to the Elliptical's power source.
I tested here to make sure that the thing was working correctly. I had someone hold the volt meter to the output wires for the USB, and I held the input wires to 9v and success!
In addition to the parts above, you will need the following:
Wire splices -- I used some from AutoZone. Probably not the most elegant, but they work...
Hot glue -- What good instructable doesn't include some!?
Patience -- duh.
Work out equipment -- (I used my elliptical but I am sure if your equipment doesn't use batteries or plug into the wall, you could do something like this.)
A loving wife -- at least one willing to let you dig into your very expensive elliptical to save a few watts...
Reebok RL 1500 Elliptical
Donor PII motherboard -- I used this to get the usb (was actually the front usb connectors) and a heat sink for the power regulator.
Throw away USB device -- You will need this to test your setup! ( I used my poopy zune!)
Step 3: CUT!
Step 4: Insert and Splice!
I recommend doing a dry run, so you can see where everything fits.
Get your hot glue gun out and glue away! I tried to make it look neat, but that isn't a main concern in this, as once it is buttoned up, it will be completely hidden!
Then splice the power from the elliptical to the wires of your regulator. I like this method as if I don't have to do any unnecessary (read: because I suck at) soldering.
If you use the splices, make sure that you get the right size. The splices I used fit the cables that i had fine, but did not fit the Elliptical's wires very well. This led to a half-hour of wondering why I was only getting very little if any voltage across them. All I did to remedy this situation was to open the splices back up, and use a box cutter to fully cut the insulation down to the wire so the metal could make contact.
Step 5: Button Up and Enjoy!
Plugged her in, and she was fantastic!