Hi CrossRoads, thanks for having a look at Femtoduino.
What's the plan for getting a bootloader in it so that sketches can be uploaded?
According to my understanding of the original Arduino UNO schematics, the programmer header is simply connected to D11, D12, D13, RST, VCC and GND so it should be possible to use ad hoc programmer cables connected to regular pinout pins to load the bootloader or to program the uC using the programmer instead of the bootloader.
Will you have some kind of socket it can be placed on top of for testing?
There are 0.05" female headers similar to those of the Arduino UNO, just smaller. For prototyping that will be the best option.
Can the pinout be adjusted to make it more convenient to connect a standard FTDI (or equivalent) adapter for programming?
I initially wanted to keep the pinout FTDI compatible. Unfortunately, I wasn't able to keep that as the necessary pins where too distant in the QFN version of the ATMEGA328 so it would have required make the PCB bigger.
So, given also the fact that it uses 0.05" headers you still wouldn't have been able to connect the FTDI directly, I decided to break compatibility with FTDI.
I plan to design a simple connector from the Femtoduino pinout to standard FTDI (following Sparkfun pinout) and/or designing it's own FTDI breakout directly compatible with the Femtoduino pinout.
Why have a 10K current limit resister for the power indicator, and then load down D13 with 330 ohm? Will the power LED even turn with ~0.3mA? ((5V-2V)/10K as an estimate)
I used the Arduino Pro Mini schematics
as starting point and 10K was the value they used in their schematics.
Given that I never designed for SMD LEDs I assumed that was a correct value.. but it looked too high also to me. I'm now comparing that value to UNO and Nano schematics and they all have very smaller resistors so it's probably an error on the Pro Mini Schematics.
However this doesn't impact the design too much as I still did not choose the specific final components so changing the value of that resistor is not a problem at all.