Standalone Arduino 8mhz internal & Software Serial


Due to power requirements, I'm going to run a standard Uno chip on it's own using it's internal 8mhz oscillator. With the chip on the Uno board (at 16mhz) my program communications via software serial to a SIM908 board at a baud rate of 9600.

When the chip is programmed with 8mhz bootloader the output baud rate is actually 4800. Presumably the software serial library thinks i'm still running at 16mhz and it's affecting it's timing.

What is the best / correct way to fix the baud rate. Would I modify software serial, or boards.txt ? If someone can point me in right direction, I'd appreciate it.

For anyone with trouble burning the 8mhz boot loader, I found only version 022 of Ardunio idea would work.

Thanks in advance.

Hello Martinamw You found any solution? I'm also running in to the same issue now.

Please advise


Create an entry in boards.txt for your board. You can look at the Pro Mini, in 5V/16MHz and 3.3V/8MHz flavour, for some of the differences. Also edit the fuses to fit your needs. See the Clock Sources section in the data sheet, how to enable the internal RC oscillator.