The circuit shown is a hacker’s contribution, and I’d want to look it over a little more closely before using it than if it were Bunnie’s design.

One consideration in the puck is that I’d like to be able to plug it into USB and have it both drive the lights and charge the battery. 16 LEDs at 25mA is 400mA total, and some LEDs I just got can probably take 50mA, so 800mA total.

I understand that USB can supply 100mA or 500mA, which means we couldn’t run 50mA per LED off USB power. But it also complicates (I think) the charging design, to try to maintain a constant current to the battery whilst the battery is being used at the same time.

Here is a link to the charging circuit on the Chumby. I didn’t realize that it was designed for a rechargeable battery. I wonder why it doesn’t ship with one.

For the past couple of weeks, I’ve carried the puck idea around in my head and thought about times I’d use it. In doing so, I’ve come up with two decisions of much higher importance to me than I had guessed at first: It needs to have a magnetic base so it can be stuck to things, and it needs to be water-resistant enough to use underwater for a few hours.

Water resistance will be far easier to accomplish if the puck doesn’t have a charging port penetrating its case, so I think inductive charging (besides being just plain cool) is a fantastic idea. Would you mind looking into that?

As a fallback plan, I’ve been thinking about the pager “coasters” you get when there’s a waiting line at chain restaurants. They have a couple of contacts on the bottom to charge when placed on a base (and corresponding pins on top to charge the next one up in a stack, but that’s not relevant here). We could probably waterproof metal pads recessed into the bottom of the case, and diode-protect the system from discharging through the pads in (impure) water.

But inductive charging would be nicer, if it can be made practicable.

Of course Wikipedia has tons.. http://en.wikipedia.org/wiki/Inductive_charging

Here is an article that had me lauging so hard I amost passed out. Yes it’s about inductive charinging.. A mouse that charges through it’s pad. Why do funny, go see for yourself..
http://www.afrotechmods.com/cheap/arnoldpad/arnold.htm

If you place the puck on top of the charging coil so that both the external and internal coils were close to each other, you should get good coupling. The primary concern will be the distance between the coils. Magnetic energy drops of very fast so the coils need to be close.

There would be some interesting experiments to try. I am not an expert but I do know that this will work. I have seen similar technology.

If you really want to try this I can do some research? I have access to an RF engineer or two who will know what we need.

If the puck is round, perhaps the charging coil can be wrapped around the outside. Then the puck could be placed inside the charging coil.