But what are some reasons they haven't implemented a 3.3V / 5V selection switch on the Arduino board (even newer revisions of the same don't have this) -- are there any possible difficulties or disadvantages to this?
@retrolefty:Looking at the datasheet graph, I see that is indeed the case (although 12 Mhz might be an option).Have you used the Seeeduino's selector capability -- I'm curious how that feature has worked out for you in general.Well I don't actually own a 328p based Seeeduino board, so I can't report on it first hand. Looking at their schematic (http://www.seeedstudio.com/wiki/images/7/7b/Seeeduino_v3.0.pdf), they are using the selector to switch a LD1117-3.3 regulator after the 5V. Seems a fairly straightforward approach.Yes, and as I said there have been several people over the years run their 'standalone' 328p projects at 3.3v and 16mhz and reported no problems, so I suspect it mostly a case of Atmel using conservative specification that has to take in worst case temperature ratings and such. I suspect it would work fine for you. It's not like the board will burst into fire and burn your house down. Lefty
And pretty much the only disadvantage to having such a voltage selector, as far as I can see, is that beginners may mistakenly leave it on 3.3V and use a 5V shield.
Many people have run their chips at 16Mhz with 3.3vdc Vcc without problems, but that is indeed working outside the datasheet specifications for the device, effectively 'overclocking' when running at that speed and Vcc voltage
I'm also regularly running ATtiny85s at 16MHz quite happily @16MHZ
Looking at the datasheet graph, I see that is indeed the case (although 12 Mhz might be an option).
QuoteI'm also regularly running ATtiny85s at 16MHz quite happily @16MHZThat's a classic if(true) statement!
Yep. But as far as the original topic of this thread is concerned:
My home brew boards all have jumpers to select Vdd = 5V or 3.3V. I've been running 328's at 3.3V and 16 Mhz fine for year now
are there any possible difficulties or disadvantages to this?
Why Not a 3V3 option? Indeed.