Mosfets will allow current in either direction if turned on. Which way current would try and flow if external power was on but below auto-switch point, would depend on which was the higher voltage, the board's 5 volt regulator or the USB voltage source.
Lefty
retrolefty:
However it's the Arduino auto-voltage selector design I really wanted to discuss. Anyone think it's a well thought out design? They certainly allocated plenty of parts and board space for it.
I'll give them credit for one major thing ... it's simple. Considering the number of beginners who get started on the Arduino, even a single jumper is likely to be confusing. Some may spend an hour pondering if it is in the right position. Others may not wonder, but leave it in the wrong position and then post that the board "doesn't work".
I think the low barrier to entry for newbies is a big positive. You don't need special USB cables, you don't have jumpers to change, you can power it in two obvious ways. The IDE is easy to use.
Then when you get to know it better you make up a custom board (like I did for my alarm clock) that just has a simple circuit with only a handful of parts. But the Arduino with its ease-of-use and its modular design (for trying out other stuff) is what got you down to the point of being comfortable with it in the first place.
retrolefty:
Mosfets will allow current in either direction if turned on.
Ah, OK.
I'll give them credit for one major thing ... it's simple. Considering the number of beginners who get started on the Arduino, even a single jumper is likely to be confusing. Some may spend an hour pondering if it is in the right position. Others may not wonder, but leave it in the wrong position and then post that the board "doesn't work".
I think the low barrier to entry for newbies is a big positive. You don't need special USB cables, you don't have jumpers to change, you can power it in two obvious ways. The IDE is easy to use.
Then when you get to know it better you make up a custom board (like I did for my alarm clock) that just has a simple circuit with only a handful of parts. But the Arduino with its ease-of-use and its modular design (for trying out other stuff) is what got you down to the point of being comfortable with it in the first place.
Don't get me wrong, I think the arduino system was a almost perfect product for the intended market. All open source hardware and software, multi-platform, I can't think of another controller platform that met all those points upon introduction. And even though it was designed for non-geeks, it's certainly drawn a lot of users with lots of knowledge and experience as well. The vast user contributed libraries is an asset that not many platforms will be able to match, now or into the future. The ease of use with the IDE and the easy transfer to standalone hardware projects is what attracted me after trying out the Picaxe platform and a little standalone PIC attempts. Arduino rocks, no mistaking that. I had made several failed attempts to learn C in past decades, but the Arduino is the platform that made it work for me.
Lefty
Wow, thanks for all of the information guys! There is definitely something for me to consider here.