UNO & ATMega328 with internal clock - Microcontrollers - Arduino Forum
Bootloader doesn't work with internal oscillator - Frequently-Asked Questions - Arduino Forum
What is the Working Frequency of Arduino UNO
Arduino pro mini @ 1MHz - 1.8V
Standalone ATmega328p
Arduino Standalone (Arduino without Arduino) | Electronics & Arduino
avrdude - Flashing a ATmega328 that came from an Arduino to not use an external oscillator - Arduino Stack Exchange
From Arduino to ATmega328 | DroneBot Workshop
My first Microcontroller project. Sadly, I do not have access to a crystal oscillator so I just accessed the oscillator of arduino uno. : r/electronics