Hello,
I have recently purchased an arduino pro mini board clone.
It seems to be a non-standard 3.3v board with a 16Mhz quartz.
This combination is not listed in the arduino IDE so I have used the 3.3v 8Mhz option both to reprogram the bootloader (flashing didn't work out of the box) and to flash a sketch.
Everything seems to work fine but the board consistently uses a double baud rate with respect to the one i set with Serial.begin: if I set 4800, then I have to set 9600 in the serial monitor to get it to work and the same happens for higher baud rates.
I suspect that this might be due to the fact that the board is expecting a 8Mhz quartz but there's a 16Mhz quartz instead.
How can I fix this? I am OK with running the board at lower rates, I don't really need 16Mhz for my application, as long as it behaves correctly.
The ATmega328 chip is not guaranteed to work at 3.3V and 16MHz according to the datasheet - in
practice some people have got this to work OK - but you are living on the edge(!).
Use any 16MHz board setting with the same version of the ATmega328 chip - the only thing the bootloader
cares about is the chip's signature bytes and the clock speed in practice for all ATmega328's. The bootloader
cannot tell what voltage the board is using!
Is this a TQFN32 or DIP28 ATmega328? Actually is it an ATmega328 even?
I would like to have a link to where I can buy such a board, as the 3,3V 16MHz combination is used in quite few RC receivers. Currently I have to replace the 8MHz crystal by a 16MHz on 3.3v promini's, to get what I want.
hmeijdam:
I would like to have a link to where I can buy such a board, as the 3,3V 16MHz combination is used in quite few RC receivers. Currently I have to replace the 8MHz crystal by a 16MHz on 3.3v promini's, to get what I want.
Just buy a 5V board and feed it with 3.3V. Look at the schematic to see what you need to modify.
Note that it will use the 328P processor outside its spec (mentioned before if not mistaken).