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Topic: ATMega @ 3.3V. Can a normal 16/20Mhz crystal be used? (Read 1 time) previous topic - next topic

JoeN

Probably a dumb question, sure hope so.  Can a normal through-hole crystal which works great on a 5V project generally be used for a 3.3V project or is there a special requirement?  I bought my crystals on the cheap and I don't have a datasheet. 

Thank you for any information.
I have only come here seeking knowledge. Things they would not teach me of in college.

dc42

If you are talking about an atmega328p then the maximum supported clock speed @ 3.3V is 13.33MHz. In practice, you may get away with using a 16MHz crystal. The crystal itself doesn't care whether you run the microcontroller from 5V or 3.3V.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

JoeN


If you are talking about an atmega328p then the maximum supported clock speed @ 3.3V is 13.33MHz. In practice, you may get away with using a 16MHz crystal. The crystal itself doesn't care whether you run the microcontroller from 5V or 3.3V.


Thanks.  I have some slower crystals - 12Mhz and 8Mhz so I guess I will use those to be safe.  Speed is not super important, the sketch has delays in it already.  The MPU I want to use is a 328P-AU (TQFP).
I have only come here seeking knowledge. Things they would not teach me of in college.

MarkT

8MHz will be easier as you won't have to compile a new bootloader, there are pre-compiled ones for 16 and 8MHz, but not 12 AFAIK
[ I won't respond to messages, use the forum please ]

JoeN


8MHz will be easier as you won't have to compile a new bootloader, there are pre-compiled ones for 16 and 8MHz, but not 12 AFAIK


I am planning on using my AVRISP2 and programming the chip directly without a bootloader.  I don't think that will be an issue using this route.
I have only come here seeking knowledge. Things they would not teach me of in college.

Nick Gammon

If you don't mind running at 8 MHz use the internal oscillator and then you don't need a crystal at all.
Please post technical questions on the forum, not by personal message. Thanks!

More info:
http://www.gammon.com.au/electronics

JoeN

I just got around to building this and when I switched it from the internal oscillator to the 16Mhz crystal it bricked the 328P-AU.  I forgot about the details on this message so I desoldered that chip and put another one in and left it on the internal oscillator.  I guess I can solder the bricked chip onto one of the other boards and try it with a slower crystal.  Bad luck I guess.  DOH.
I have only come here seeking knowledge. Things they would not teach me of in college.

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