Hi All and thanks in advance for the help!
I have created a few boards using the ATMega328P (-AU) at 5 volts but I am now trying to create one running at 3.3 volts so I don’t have to use vltage dividers on my logic interfaces.
I have looked at these two posts, which are helpful, but I still have a few questions:
Based on my [probably too limited] understanding of the info in these posts, I have tried to upload the bootloader to my board as if it were an Arduino Pro Mini using the Arduino as ISP method. No luck.
The first post tells me that I need to run the 328 at no more than 12 MHz:
Can anyone recommend a good external 12MHz resonator that is hand-solderable?
I’m pretty good hand-soldering SMTs down to about 1206
Prior to loading a bootloader, I am guessing that the 328 runs off the internal clock
If I supply 3.3v to it will it configure itself appropriately to receive my bootloader? Or
perhaps it sees that I have an external clock hooked up and just uses that?
The second post tells me “You need an 8 MHz bootloader on the chip, if it is running at 8 MHz. You will need an ICSP programmer to do that.” (thanks jremington). Of course I am looking for 12MHz but point taken. I am assuming that an Arduino Mini or Pro Mini running at 3.3v must also be limited to 12MHz and therefore the Arduino as ISP should be trying to load my board with 3.3v settings (brownout detection < 3.3v and clock at 12MHz).
Bad assumption on my part?
Do I really need an ICSP programmer?
The first post also tells me that I can look at hardware\boards.txt. I am running the Arduino IDE on a Mac and I can’t find that. Can anyone tell me how to find that file?