USB and Arduino: Power Arduino, charge LiPo, and transfer data at the same time I was hoping to design my own Arduino board for a recent project of mine, a portable project that was powered by a 3.7 LiPo battery. Most ideally, I wanted to replace the USB B port with a single USB Micro port that implements the following features:


Provides power to the Arduino while it is plugged in (just like a regular Arduino does).
Connect the D+ and D- pins of the USB to the Arduino somehow to allow for on-board programming (however the Arduino accomplishes this already, I'll refer to this as the "onboard usb/serial converter"). I want it to keep it programmable on-the-go.
Charges an on-board 3.7V LiPo Battery. I was hoping to use Adafruit's PowerBoost 500 Shield as a reference for my schematic.


However, I haven't been able to find a schematic or example that implements all 3 features above at the same time from the same USB port. I don't have much experience with charging circuits, so the following questions might sound dumb. Below are some solutions I was thinking of that probably won't work, but I wanted to make sure:


Connect the Output Voltage of the LiPo Battery to the V+/GND supply of the USB cable (probably not safe to connect all V+ sources together). 
Just connect the D+/- data cables to the "onboard usb/serial converter" without connecting the Vbat/Vusb somehow, have the USB V+/GND connect to the LiPo charging circuit, and the Battery Voltage power the Arduino.


I know some devices have this charging/data-transfer functionality (e.g. my phone can transfer photos to my computer while being powered on and charging at the same time), but I'm wondering how it's possible to have similar functionality for an Arduino board. Any advice?

Absolute worst case, I'll just have 2 USB ports, one for charging the LiPo and one for Serial Communication/Programming

EDIT: The idea of using an ATMega32U4 seems appealing (despite the 3.3V vs 5V operating voltage), mainly because it has a pin for VBUS for USB and Vcc for main power. But I was wondering how to do this on say an ATMega328P that doesn't have a pin for VBUS.
I'd recommend using the Arduino Leonardo as a reference for your circuit. Its pretty much the same as an Arduino UNO but has a built in USB interface so you don't need the USB-Serial converter.

I'd also recommend running the chip at 3.3V. That way you can use a linear regulator to regulate the 3.7V battery voltage down. Otherwise you'd need a boost converter to bump the voltage up to 5V which needs more parts.

If you follow those recommendations then all you will need is a LiPo charging IC to handle the charging. You'll need to add an ISCP header to flash the initial Leonardo bootloader, but after that you can use USB and the Arduino IDE to program it.

I did exactly this for a school project a while back. You can find the schematics here: https://github.com/seanwatson/ece4416-project/blob/master/hardware/rev2/sw-4416-project-v2-sch.pdf