I am making a Uno for a battery powered project, and I just want some opinions on whether anything looks incorrect in the schematic. I have added a few things that the Uno doesn't have, such as digital pin protection, plus the power LED only runs when the board is connected to USB. Does it look right to anyone here? Are there any ways I can use even better components for using the least milliamps possible?
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For a battery powered "Uno" I'd drop the USB stuff. Just leave an FTDI header (assuming you add a bootloader) and/or an ICSP header
Can you explain what you are doing with Q2 and D4.
Built in resistors on GPIO pins are not normal. You may get problems, for example, with SPI peripherals.
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I thought about this. But I want to find some way of disabling the USB interface when the board is powered by the VIN pin/barrel jack. Q2 and D4 are supposed to be the LED on pin 13.
This is what I was told be someone in a private message. I tried to follow their advice there, but I think I did it wrong.
I was told by someone that they did this without any issues.
You are shorting Vin to GND ! 
The center pin is Positive
Oops. I wired that wrong.
Just follow the UNO schematic:
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I was hoping to use the half of the LMV358 that Uno uses for the pin 13 LED for the power LED instead:
Power LED is a simple circuit, save the 358 for D13.
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Here you go:
Is pin 6 and pin 7 of the LMV358 supposed to be connected? One goes to SCK, and one goes to 13. But both SCK and 13 are directly connected to the same digital pin, and header pin.
6 is connected to 7.
This has the NET called L13
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So my schematic is correct?
I am having some difficulty of justifying the expense of the from-scratch construction of a clone UNO. Most members use the "mini" clone for such needs as it is inexpensive and can easily plug-in to a DIP socket made of header strips.
At 16MHz, the minimal UNO is extremely sparse in parts: xtal, 2x load cap, ATmega328P, connection for +5V. An optional USB-serial permits programming with a bootloader.
Understandable. But I can build it for $20, which is cheaper than a genuine Uno anyway.
I specifically want to be able to use Uno shields on it though, and I'm trying to make a circuit that shuts off the USB chip when the board is using the VIN pin, mostly just because I want to see if it is able to be done.
Can I just build a simple NPN transistor switch?
Yes. But I want it to do this automatically (a manual override such as a jumper would be nice though).
