I have built an Arduino on a breadboard (using an ATmega328PU) with an 5V FTDI USB controller.
I want to be able to run the Arduino at 3.3V instead of 5V.
It works completely at 5V supplied by the FTDI controller, including USB serial from the Arduino IDE to the FTDI controller.
I am using a voltage regulator to lower the FTDI controller's 5V down to 3.3V (I have checked and its always 3.2-3.4V out) to power the Arduino. Everything works (it can power some 3.3V sensors and run my sketch), except I can't communicate with it over USB serial at all.
I have a 22μf cap between the DTR line and the ATmega's RESET pin and I have a 10k resistor on the ATmega's RESET pin (from tutorials the 328PU needs both for uploading sketches), and it works at 5V.
I have tried an NTE4050 non-buffering inverter to convert between the 3.3V and 5V signalling and it still doesn't work. Has anyone tried that?
For serial monitoring (which doesn't work at 3.3V either) I am running at 115200 baud but I also can't upload sketches which is at a lower baud rate (19200?).