UPDATE: I now have a couple of lithium polymer powered rechargeable MintyBoosts.
Lady Ada of Adafruit Industries sold me on yet another kit, the MintyBoost. It’s a USB charging device that fits into an Altoids chewing gum tin.
I ordered one entire kit, plus five extra PCBs and MAX756-CPA+ power regulators from Adafruit. From other vendors such as Maxim IC, Mouser, DigiKey, and Futurlec, I bought parts enough to build at least 25. Looks like I’ll have to either make my own circuit boards or order more from Adafruit.
So far I’ve built five of them – the original yesterday afternoon and the other four in the past three hours using parts I already had on hand. Her instructions to “Case It” make use of sheet metal snips and cut through the rim. I don’t like this as the tin’s structural integrity is now compromised:
I have a Dremel, so I used a cutoff wheel to make three incisions: two parallel with the top edge and one diagonally, making a “Z”
The two resulting flaps can then be bent inwards a bit and snipped off and pressed tight against the inside wall. I need to practice a bit more making the cuts as I made the hole too large on four of the five. On the fourth, I tried to get as close as possible to the correct dimension, but it was too small. Then I made it too large by over-correcting.
It still works just fine, though. I have successfully tested each with the portable electronics I have:
- HTC Dream Dev 1
- Garmin Nuvi 660 GPS
- Lexar 1GB LDP-600FB MP3 player
- iPod 2GB Nano
- Sony Ericsson 750i cellphone (reportedly must be pull-down resistor configuration; further testing required)
- Sony Ericsson W800 cellphone (reportedly must be pull-down resistor configuration; further testing required)
The difference between using a pull-up or pull-down resistor is due to the fact that the USB standard is just a document and therefore interpreted in any number of ways when a manufacturer implements it. As such, some devices are designed with the need to see a particular voltage on the data bus even though it’s merely charging while others don’t care one way or the other. It seems that the newer iPods, in particular, need to see that voltage.
I think one of the modifications I will make is a slightly larger tin such that the USB jack will be flush with the tin’s wall and two sets of batteries in parallel for a longer run time. Perhaps a Penguin tin for a super dweeby Linux theme, or an Altoids mints tin? If I can contain the costs, a rechargeable LiPoly will be in the works.
However, as built, they’re inexpensive, fun and easy to build, and work exactly as advertised. Highly recommended!