I have a Arduino Uno.
http://arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdf
I want to power Arduino using rechargable Lithium polymer battery,
through ICSP's 5V and GND pins.
ICSP might not be the best place, but I want to know if ICSP is possible for this, because every Arduino has it.
So when the Arduino's USB is connected to PC and Arduino is able to get power from USB bus, I want to charge the battery through the board on top of ICSP pins.
When USB is disconnected, and the battery is full, my board provides 5V to Arduino.
I understand that my board needs a current control IC (ex: max1555) to safely charge Li-Po battery, and a way to convert Li-Po's voltage to 5V.
Is there something else that I have to worry about?
Does Arduinos accept 5V from ICSP and work properly?
Best Answer
I don't think this is necessarily safe. The Arduino Uno has two power supply options - USB and through the barrel jack. If the barrel jack is used, the USB power is disconnected through comparator U5A and Mosfet T1. +5V is derived from either USB (directly) or from the barrel jack (via regulator U1).
Feeding +5v directly to the +5V lines would not 'trigger' the USB power shutoff. Whether this is an issue for the USB device feeding the Arduino or not I'm not sure but I wouldn't bet on it.
More information here (similar question): Arduino Uno R3: Directly supply regulated 5V to 5V pin?.
I'd suggest using a similar 'shut off' on the Lipo supply that shuts off the Lipo supply is the USB is connected (assuming you are using a charging circuit this should not necessarily prevent you from charging over USB). Really what is boils down to is 'how do I build a USB powered Lipo charger / power supply'.
Another option would be to use a USB powered Lipo charger/booster board like Sparkfun's Power Cell - LiPo Charger/Booster. You'd basically power the Arduino using the board - using the board's USB power in stead of the Uno's USB port. As Sparkfun has all the schematics for the board on their website (https://www.sparkfun.com/products/11231) you could also re-use their design to 'integrate' if with your design. Similarly, you can have a look at how the Arduino Fio (https://www.sparkfun.com/products/10116) does it - it has an integrated Lipo charger.
From what I can see, all these work the same way: use the USB +5v line to power the battery charging IC. Then connect the battery to the voltage regulator. It wouldn't be too hard to modify your Uno to work like this - just cut the USB +5V trace and basically drop the charger/lipo in there.