I plan to run the atmega328p without external oscillator like in this tutorial:
Some guy here saying:
"The internal oscillator does lead to inaccuracies but I2C is one of those protocols that does not require a synchronized clock with the device it's interfacing with, so no I2C will not be adversely effected by the internal oscillator. The protocol that does require a higher level of accuracy is UART or 'Serial'. Without getting into too much details the faster your baudrate of your UART the more likely there is to be errors. So if you are going to use a UART with the internal oscillator just try out a baudrate like 115200 and see if there is garbage outputting to the Serial Monitor if so reduce the baudrate to 57600. I've personally seen garbage come out on 115200 but that was not consistent. It's probably because the oscillator is temperature dependant."
Could using the internal oscillator cause a problem with wireless communication with 433MHZ RF transmitter using the VirtualWire library?