I'm trying to improve my electronic knowledge for several months ...
I just built my first my self dev board in order to interface a pellet stove including a atmega328p, a Lora transceiver and a ftdi usb interface. All based on 3.3v voltage.
All seems to works well except usb programming!
Actually, I already bought a ft232 board and I never achieved a usb programming.
So I investigate more with the ft232, atmega328p and a breadboard.
I finally performed a programming in this cases:
A 5v supply with an external oscillator ( 8 mhz or 16 mhz) and a RC circuit between DTR from ftdi and atmega's reset (10K and 0.1uF)
But it didn't work when I switch to 3.3v or when I used internal oscillator (with proper bootloader burning).
Do you have some ideas why I can't program with 3.3v?
I looked on reset time (with the very good OLS logicsniffer project) which is different linked to voltage: around 0.6ms for 5v and 1.2ms for 3.3v so I put 2x0.1uF in series to be similar but no way, it still doesn’t work ...
I have no more idea now ...
I hope someone can help me.
Thank's in advance, and sorry for my bad english...