Arduino 3.3V and LiPo UPS

[system]

I'm looking for an easy and smart way to have a 3.3V Arduino PRO mini with one little LiPo (1 cell only - 1S) embeded, acting as UPS.

LiPo must to be on charge when external power (from DC or USB) is available and feeds Arduino when DC or USB is unplugged. Of course, Arduino mustn't turn off in the meanwhile!

I know that Olimexino does it and I would like to do the same with Arduino PRO mini.

I don't want to use shield. It must be a very cheap solution. I found a couple of ICs that could be useful: MAX1551/5 and ltc4071.

Has anyone already worked on this matter?!

[MichaelMeissner]

One solution would be a battery charger like Adafruit sells. You hook the battery up, and if there is external power, it uses it to charge the battery. You can charge while the Arduino is running. Adafruit sells 3 different modules of charger that you can power the chip while charging the batteries:

• USB/DC Lithium Polymer battery charger 5-12V [3.7/4.2v cells] : ID 280 : $17.95 : Adafruit Industries, Unique & fun DIY electronics and kits - Can charge the battery from a mini USB plug (5v) or a 2.1mm DC adaptor (5-12v);
• USB LiIon/LiPoly charger [v1.2] : ID 259 : $12.50 : Adafruit Industries, Unique & fun DIY electronics and kits - Can charge the battery from a mini USB plug (5v);
• USB / DC / Solar Lithium Ion/Polymer charger [Rev C] : ID 390 : $17.50 : Adafruit Industries, Unique & fun DIY electronics and kits - Can charge the battery from a mini USB plug (5v) or a 2.1mm DC adapter (5-6v). This is designed to be charged from solar power and will automatically draw the most current possible from the panel in any light condition.

The chip Adafruit uses for the first link is the MCP73861. The MCP73833 is the new replacement for the MCP73861 (the biggest difference seems to be the MCP73861 can use input voltages up to 12 volts, while the MCP73833 can use voltages up to 6 volts, which is where the limits for the other boards come from).

[system]

Thank you, but it looks to me a simple li-po charger, not a power back-up solution (UPS).

[MichaelMeissner]

Qbert:
Thank you, but it looks to me a simple li-po charger, not a power back-up solution (UPS).

Maybe I'm not understanding what you want. Quoting from the page:
2 JST connections so you can keep the battery plugged in and powering your project

As I understand it, if you plug in the battery into one JST connector, plug your board into the other, it will run from the battery. If you plug in power via USB or DC current, it will charge the battery and allow you to run the Arduino.

If you need to switch between two power sources, perhaps you want something like this (but it wouldn't charge the battery without additional circuitry): Pololu - FPF1320 Power Multiplexer Carrier with USB Micro-B Connector

[CrossRoads]

I used a MAX1811 in my RF remote control.

Mixed-signal and digital signal processing ICs | Analog Devices

Plug in 5V source (USB port) to charge, battery takes over when charge source is removed.
It installs in the socket on the left in this picture, a couple or Rs & Cs to support it go on the right. I should take a new picture!
A 1000mAH LiPo flat battery is secured to the bottom of the card.
I've posted the schematic for it before, will see if I can find a link.
http://crossroadsfencing.com/BobuinoRev17

[CrossRoads]

Here's a thread showing the MAX1811 in another design I was contemplating, a simple 5 button remote replacing the 16 button keypad:
http://forum.arduino.cc/index.php?topic=112798.0