• 3.3V:
  • Voltage regulators: KB33, S20K, F34V, L0RA, L0RB
  • Oscillators: 80e., 80'0
• 5V:
  • Voltage regulators: KB50, L05, L0UA, L0UB
  • Oscillators: R160JAC6s, 16.000-30, A1, A'N, A'a

https://arduino.stackexchange.com/questions/8511/how-to-identify-arduino-mini-pro-5v-vs-3-3v