I am wondering if this Arduino UNO R3 clone is clocked at 12 MHz instead of the standard 16 MHz? On the board, you can see there is 12.000 written on the crystal oscillator. clone1

But maybe it's not the MCU clock speed? I found this other clone, which has 2 crystal oscillators?! One is 12 MHz and the other one is 16 MHz. clone2

I can't figure out what's happening with these boards... Are these sporting faster or slower speeds? The original Arduino UNO R3 has only one 16 MHz crystal oscillator.

  • look at the leftmost component between C5 and C6
    – jsotola
    Aug 3, 2019 at 23:53

2 Answers 2


The 12MHz crystal is for the USB interface.

The main MCU uses a very small 16MHz resonator, which you can see between C5 and C6.


The 16 MHz resonator, a 3-pin part, can be seen between C5 and C6 in the first picture.

The 12 MHz is for the CH340 as noted.

So it's not an Uno, but a clone ripoff, as an Uno would have a Atmega16U2 for the USB.

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