I hadn't burnt myself with a soldering iron in a long while (because I hadn't used one in a long while, not because my skills with one had improved :-) so I thought I would look for some projects to play with. I found the Minty Boost. This looked like a reasonably easy to make and useful little project, so I ordered some of the bare PCBs, opened an account at DigiKey ('cause I just knew there would be more fun things to build later) and bought some Altoids chewing gum.
Once I had all the parts, it was time to do some soldering. Ladyada's instructions are quite good, so I won't get into the details of constructing the kit. I will, however mention the few places where I deviated from the instructions. My deviations were intended to strengthen the USB connector, not to make up for any defect in the kit.
As you may have guessed, I like silicon adhesive. It will bond pretty much anything to anything else, yet it is flexible enough to help absorb some of the abuse that connectors invariably have to deal with.
I also built a second one, but used two D cells instead of the AA cells. Of course, this won't fit into the Altoids tin, so I have just stuck the PCB to the back of the battery holder until I find a good case for it.
Now that I have my Minty Boost, what to charge? I can think of two things I own that charge off of USB, my BGT-11 GPS and my Openmoko Neo FreeRunner.
The BGT-11 just worked. No muss, no fuss. I just plugged it in and it
started to charge.
The FreeRunner has an interesting setup for the charging circuit. It will draw either 100mA, 500mA or 1A depending on a few things. The default is 100mA, but if it can, it will negotiate higher with the host. Also, it can identify the wall charger it came with by a specific resistor installed on the ID pin of the mini USB-B connector. It will draw 1A from the wall charger.
Since the Minty Boost can not do the USB negotiations, the FreeRunner
will only draw 100mA. This current is not sufficient for the FreeRunner
to charge the battery, instead the Minty Boost is essential an external
power pack. It will extend the FreeRunner's battery life but won't
charge the FreeRunner and is insufficient to operate the FreeRunner if
its battery goes dead. If you look at the picture, in the upper right
hand corner, you see the battery strength indicator. This indicator
means that the FreeRunner is not charging.
Fortunately, I can override this in software. I wrote a shell script
that forces the FreeRunner into 500mA mode and created a "Minty" icon to
launch it. I tap the Minty icon and if you look in the upper right hand
corner, the indicator has changed to a lightning bolt. That indicates
that the battery is charging. The photograph of the screen is a little
difficult to read, so here is a screenshot that is much more clear.