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Topic: Using ATMEGA328P-AU with 8mhz crystal (Read 109 times) previous topic - next topic

SouthernAtHeart

This is my first project using an Atmega328 with an 8mhz crystal.  Do I just burn the bootloader by selecting arduino pro mini, 8mhz?

I'll be powering it at 3.3Volts. 
thanks.
(I have a 3.3V FTDI cable)

musskopf

Yes, any 8Mhz Bootloader should do the trick. Just make sure you check the fuses values to confirm the external crystal is being used and not the internal oscillator.
http://talk2.wisen.com.au

SouthernAtHeart

The smallest 8mhz crystal I can find on Digikey is this one by Diodes Inc.
It has these specs:
Frequency 8MHz
Frequency Stability ±30ppm
Frequency Tolerance ±30ppm
Load Capacitance 18pF
ESR (Equivalent Series Resistance) 100 Ohm
Operating Mode Fundamental
Operating Temperature -40°C ~ 85°C

This should work okay?  Do I use 22pf caps, like I normally do?

ron_sutherland

Have a look at this:
https://blog.adafruit.com/2012/01/24/choosing-the-right-crystal-and-caps-for-your-design/

So 22pF is probably good enough, especially if the stray capacitance is a little high 8pF (e.g. from ground plane pour).

hansibull

The easiest solution is to use the internal 8 MHz oscillator. This requires no external parts. Everything you need can be found here --> https://github.com/MCUdude/MiniCore
MightyCore -  ATmega1284, mega644, mega324, mega164, mega32, mega16, mega8535
Github.com/MCUdude/MightyCore

MiniCore - ATmega8, mega48, mega88, mega168, mega328
Github.com/MCUdude/MiniCore

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