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Hi! i want to make a standalone setup, and since the project is not computationally intensive i want to keep the pcb small and simple.
1)If i set the atmega to work with the internal clock, can i still power it with 5V? or i need to give it 3.3V? i have a pir and other stuff on the board that is 5V so if i have to use two voltages on 8mhz it no longer makes sense.

2)not directly related to my project, if run the atmega at 8mhz how are pwm/timer(s) library affected? does delay and similar functions work as advertised? someone says that the internal 8mhz clock is not stable, what kind of applications can have trouble with it?

Thanks!
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Hi! i want to make a standalone setup, and since the project is not computationally intensive i want to keep the pcb small and simple.
1)If i set the atmega to work with the internal clock, can i still power it with 5V? or i need to give it 3.3V? i have a pir and other stuff on the board that is 5V so if i have to use two voltages on 8mhz it no longer makes sense.

5v will work fine.

2)not directly related to my project, if run the atmega at 8mhz how are pwm/timer(s) library affected? does delay and similar functions work as advertised? someone says that the internal 8mhz clock is not stable, what kind of applications can have trouble with it?

Thanks!

Everything else works OK. The stability issue is that the actual clock speed will vary according temperature, much more so than with an external crystal or resonator, but unless you need a high accuracy clock rate for some reason in your application, usually not an issue.
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Perfect! Thank you!
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I understand you want a PC board.  If you ever want a low-profile 328P-PU on a breadboard / stripboard, this is a very easy build:

http://www.instructables.com/id/Build-A-FLAT-duino/

My prototype is using a 16MHz, but it is optional ... Just mind the fuse settings.


Ray
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For stability of the internal clock look at the datasheet: http://www.atmel.com/dyn/resources/prod_documents/doc8161.pdf

On pages 417, 418 fig. 29-174 and 29-175 show you how internal clock frequency varies with temperature and supply voltage. It depends on your application if this is stable enough for you.

Elektrix
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