This plus an LDO may do the job. http://www.adafruit.com/products/390 (Although it's currently out of stock) Matt I have a small sensor monitor system which uses Zigbee (Xbee 2.4 Ghz models) to send back various telemetry from my 5 acres of land. Thus far, the only one I have actually built and installed is a swimming pool temperature monitor, but I plan on having that station do double (or triple) duty eventually, and monitor things like air temp, wind speed and direction, solar radiation, etc. I have need of two or three locations to put these critters where it will do things that are "slow detection" type events: opening of a mailbox, detecting someone driving up the driveway, etc. Yes, I'm just that geeky. The pool sensor bundle consists of 4 DS18B20PAR+ temp sensors, a 3.3v Arduino "mini mega" with entirely too much I/O for what I need, and a Xbee. I've got most things on the Arduino turned off, unused lines are configured as inputs with pull-up resistors to keep them from floating, etc. I also sleep the Xbee other than perhaps 1 second out of each 60, when there is something to be transmitted. I don't currently power the DS sensors up only when needed; they have a fixed resistor tied to Vcc for now, but I intend to instead use an additional I/O line from the Arduino to supply power only when needed. I also slow the clock down to the minimum, which and a timer tick happens once every 3.4 seconds or so, where it wakes up briefly, sets the clock back to 8 Mhz, checks to see if we have something to do, and if not, sets the clock down to minimum and sleeps again. Using the Vcc monitoring built into the Xbee, I have seen a 0.02 V drop in 4 days, powered off two standard alkaline AA cells. What I'd like to do is find a LiPo charger with 3.3 V DC output, a solar input, and as an option an external DC supply. As I live in Oklahoma, I think the biggest problems are keeping the LiPo in the proper temperature range, not a supply of sunlight. However, I'd obviously like to keep things plunking along all night. My ideal system would include: (1) 3.3 VDC output. (2) Solar input. (3) DC input, say from a USB or wall-wart. (4) A wide range of LiPo capacities. (5) The ability to intelligently use (2, 3, 4) together such that it will take power from either (2) or (3), use the excess to charge (4), but will use combinations when (say) the sun is low but does provide SOME power, but not enough. That is, it will only augment solar with the LiPo when needed, otherwise it could run entirely off solar even if the LiPo is otherwise full. (6) Some logic-level indication about the power source, or if the LiPo is being drained, charged, or is "idle." (7) A logic-level indication about the charge on the LiPo. I know, a long list of desires. Anyone know of such a beast, ideally one I can buy rather than build? Exploding LiPo does not smell good in the back yard. Thanks! --Michael -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .