5V Atmega 328P-AU on 3.3v

Hello everyone, I have a question regarding running a 5V Atmega328P-AU chip on 3.3v at 8MHz.

Up until now, I have always used 3.3v Arduino pro minis to run on my custom 3.3v Arduino development boards, I have noticed though that whenever I use an Atmega chip from a 5V Arduino pro mini, it simply won't upload the code and won't work. They are technically the same chip?

I am nearly certain that this is due to the bootloader and I can just bootload the chip on a 3.3v Arduino pro mini but I have not had the chance to test it out yet.

Is it just a matter of uploading the 8MHz 3.3v bootloader?

thanks

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. This one works extremely well, for both 3.3V and 5V boards.

That pololu is indeed a very nice programmer and usb-to-ttl in one device.

I don't regret ever buying it.