I usually walk to work every day, and this year when winter started to rear its ugly head I decided to do something about it and buy a USB rechargeable hand warmer. It works great except for the fact that I would leave it in my jacket pocket and forget to charge it until it was totally dead, so I solved this problem the best way I know how: more electronics!
To make sure my USB hand warmer is always charged up when I put on my jacket, I cut a USB cable at the end and soldered the wires to copper tape on a clothes hanger:
When I hang up my coat, the electrical contacts on the hanger meet up with some conductive fabric sewn to the inside of the shoulders. The fabric is sewn with conductive thread to wires that carry the charging current down to a USB cable in the jacket pocket. I used wires for the charging conductors in this project because they’re insulated to prevent shorts and they can carry more current than conductive thread so anything plugged into my jacket will charge as fast as possible.
There’s also an LED sewn on to the collar of my jacket that lights up when it’s receiving power from the hanger so that I know it has a solid connection. The LED is sewn in with conductive thread instead of wires because it only needs a small amount of current in order to light up.
Now I can just leave my hand warmer (or any device that charges from USB) in my pocket and it’ll get topped off whenever I hang up my jacket. No more icy fingers!