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I need to use atmega328P without arduino board, so far I know that I will need 16MHZ Quartz Resonator and two 22nf capacitors. However, I have seen that other people are using atmega328P without capacitors.

What is the role of those capacitors? Can I use atmega328P without capacitors?

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    You need 22pF (picofarad) capacitors, not 22nF. – tttapa Jan 30 '18 at 15:21
  • You also need power supply bypass capacitors. – Chris Stratton Jan 30 '18 at 15:57
  • you can use it without caps and with a crystal, at half speed, but maybe half price too – dandavis Jan 30 '18 at 21:57
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Those specific capacitors form part of the resonant clock oscillator circuit. If you are using a quartz crystal then they are required. You can't do without them.

If you use a 16MHz ceramic resonator, however, they don't need the capacitors (they're built into the resonator).

Also, if you have your ATMega328P on a breadboard the capacitance of the board itself is sometimes enough to "get it working", though as soon as you transfer your circuit to a permanent PCB it will suddenly stop working for no apparent reason.

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    One could also use the build-in 8MHz RC oscillator, and remove the crystal entirely. – Gerben Jan 30 '18 at 15:51
  • @Gerben Indeed. Or use an external clock source, like a MEMS oscillator. – Majenko Jan 30 '18 at 15:51

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