ATmega328 fuse settings for changing 'brown-out' - need help

I have a standalone ATmega328P running at 8Mhz internal clock powered by 3.3V. Problem is it is still running with a 8Mhz stock bootloader which has a brown-out detection at around 2.7V or so. I want to lower it to 1.8V or disable brown-out altogether.

I have found out from various versions of boards.txt files around the Internet that by default the extended fuse is set to be 0x05, which has to be 0xFF for disabling brown-out, or 0xFE for 1.8V. I tried to bootload the chip with just this value changed from 0x05 to 0xFF, but got that infamous avrdude sync problem error. If I don't change this value, bootloading succeeds.

Is it possible to just change the extended fuse keeping the bootloader as it is? If yes, how can I do that?

Or what is the best and/or the easiest way of uploading ATmega328 8 MHz internal clock bootloader with brown-out detection level changed or disabled?

Any help would be highly appreciated.

I have just figured out that unlike the high and low fuses, the extended fuse has only 3 bits. Not setting any one them (i.e. disabling brown-out) the value of efuse would be B111 = 0x07. (It was confusing at first, not setting is 1 and setting is 0).

Anyways, after changing 0x05 to 0x07 in the boards.txt's efuse setting, I have been able to burn the bootloader of ATmega328P with interbal 8Mhz clock. Avrdude process and messages went well, verification went Ok. Now do I need to check (or do I have a way of checking) whether the brown-out has actually been disabled?

Any news ?

I want to ensure that only changing highfuse but using same bootloader i will not make anything wrong fot these little chips.

Could you tell me your experience ?

Best regards,

Sayedurrchowdhury:
I have just figured out that unlike the high and low fuses, the extended fuse has only 3 bits. Not setting any one them (i.e. disabling brown-out) the value of efuse would be B111 = 0x07. (It was confusing at first, not setting is 1 and setting is 0).

Anyways, after changing 0x05 to 0x07 in the boards.txt's efuse setting, I have been able to burn the bootloader of ATmega328P with interbal 8Mhz clock. Avrdude process and messages went well, verification went Ok. Now do I need to check (or do I have a way of checking) whether the brown-out has actually been disabled?

Thanks! I just edited the efuse on the text file and it worked! Lowest I went with the blink sketch is 2.25v and it is because I could no longer see the LED blinking, (it was very faded).