I’ve built at least two dozen MintyBoosts – some with 4 x AA alkalines, some with rechargeable 2 x A123 NiCads, and of course the standard 2 x AA – and finally decided to build a rechargeable version. I’ve long had the idea, but wasn’t too keen after doing a bit of research on lithium polymer batteries and what is truly meant by “vents with flame” (see this and this, for just a couple of examples). I finally got over the fear and built two in a single morning. I used LadyAda’s MintyBoost circuit board, SparkFun’s LiPo charger, and a couple of the dozens of mint containers I have sitting about. The larger tin contains a 2200 mAh battery I got from RapidRepair for a measly 6 bucks (purchased 3, actually) while the smaller uses an iRiver Clix 720 mAh battery I got from BatteryShip (and cost more than 3x more than the 2200, though it did come with a nice set of minature tools).
My SparkFun charger is an older version of the one depicted at the link above, the only difference being that mine didn’t have the JST (?) connectors. I had originally purchased and planned to use SparkFun’s 2000 mAh battery and decided on a layout which required a bit of modification to both the battery and the charger such that everything could be attached to the bottom of the tin – no mounting of components on top of the battery. When the 2200 mAh iPod batteries arrived, I was pleased to discover that they were perfectly suited the task, but because it was larger I’d have to place the recharging and boost circuitry on top of the battery. Not a problem, really, as for a number of years I made a living installing Nortel and Alcatel SONET equipment and have a roll or two of fish paper electrical insulation left over. I cut the fish paper to size, used spray-on adhesive to glue it to the battery, hot glued the battery into the tin, then aligned and hot glued the circuit boards to the fish paper.
The mini Penguin was a bit different. I had to desolder the DC barrel jack from the board and cut as much off of the board behind the connector solder pads as was possible. I didn’t modify the boost circuit board, but when I do another one I’ll do a bit of reconfiguration to avoid having to cut a hole in the lid. I think next time I’ll eliminate the 8-pin socket and solder the uC directly to the board to get it out of the way – it *barely* closes as it is. I also need to find a shorter inductor. I’ve pulled parts from tons of old electronics boards, but have yet to find a suitable part, probably an SMT (surface mount) part. And while I’m at it, replace everything I can with SMT. Heck, it might even get to the point where I actually make my own boards designed specifically to use SMTs.
In testing, the larger unit recharged my Android Dev 1 with no problem. Hardly a dent in the 2200 mAh battery. However, the Lil Penguin didn’t fair so well. It took my Dev 1 to only about 65%. That isn’t bad, though, and it’ll do in a pinch. The key here is that the device is only for emergency use and it’s tiny, so I’m driven to improve the design.
Yeah, yeah. I rarely post. I have a job that keeps me busy flitting about the US from Miami to Syracuse to Seattle to San Diego and most major metros in between.
LadyAda says it shipped today, so I hope to have it by Saturday. It’s kinda like a Chumby, but mostly not. It’s similar in that it outputs PAL or NTSC composite video to a display using widgets, but not as it doesn’t come with an AC adapter, a display, or a furry cover. Nor are there many widgets as of yet. Hopefully, with time, more will come. But not from me, alas. I took many, many coding courses back in my college daze – assembly, basic, pascal, pl1, fortran, c, and one or two others – but didn’t understand that I needed to focus on becoming fluent in just one, then move on to a new language, one better suited to what I wanted to accomplish. I was young, petulant, foolish, wasteful of time and money, and so cannot code worth a damned in any language. While I’m no longer so young…
I ordered a display, a PSOne screen which runs anywhere from $40 to $100. I considered the Pyle 7″ widescreen which is 2″ larger and more versatile, but settled on the PSOne due to price. Besides, I can hack the PSOne to be portable using ExtremeTech’s tutorial on how to substitute white LEDs for the high voltage backlighting bulb, thus allowing it to run on just 5V. I’ll eventually find an enclosure and drop in a LiPoly battery and charger circuit I got from SparkFun some time ago. I picked up a couple after selling a number of MintyBoosts, deciding to develop a self-contained rechargeable version. However, I gave it second thoughts upon realizing exactly what the warning “Vents with Flame” means after watching this video of a LiPoly pack “venting.” Most decidedly an understatement.
I’ll update after getting it assembled.
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.
UPDATE II: Edited links to Makezine’s protoshield and TodBot’s candle light code.
UPDATE: I’m an idiot. Once I removed the protoshield, I saw that the board has clearly marked these pins as PWM! D’oh! I guess I got too comfortable using the shield and never bothered to actually look at the Diecimila itself.
Hmmm… I was modifying Todbot’s candlelight effect code to use multiple LEDs, but it seems that only certain ports on the Arduino allow such (3, 5, 6, 9, 10, and 11); the others merely flash on/off. The whole point of the code is to illuminate the LED in varying brightness such that it looks like a flickering candle.
I’m using this particular prototyping shield (others can be found here, here, here, or here) and ran the tests again on the bare Arduino, but found nothing wrong with the shield. I need to research this to find out why. I’ll update this post when I discover the reason.