Changing Speed of Arduino

Hey Guys,

I’m trying to find some information on how to change the speed of my arduino, and I haven’t had any luck. Is there a page or forum posting that’s discussed this before?

I assume that swapping out the crystal/resonator would just work, but that all the arduino timing functions would be wrong (millis, PWM, etc). I remember reading about how to make the changes and reburning the bootloader(?), but I cannot seem to find this info now.

While I’m on the topic:
What is the minimum speed acceptable?
What are pro’s & con’s of a crystal vs. a resonator?

I want to do this to obtain maximum battery life for projects that don’t require speed.

You can use the Atmega8 bootloader in the 168 to use the internal 8 mhz oscilator.

Thanks! Burning bootloaders is straightforward enough, but I assume that the lack of discussion about modifying them probably means it’s well outside of my ability at current.

So the Atmega8 bootloader already has the fuse bits set to use the internal oscillator? It looks like every old ‘full’ arduino board that I looked at had the 16MHz crystal. Do I simply omit the 16MHz one from the circuit or is something else needed?

The datasheet suggests it will go down to 32kHz operation (would call for a 256kHz oscillator?)

I think eried is slightly mistaken - its the lilypad bootloader that uses the internal 8MHz oscillator.

If you want to uses a 32kHz crystal, common for clock applications, check out this thread on ladyada’s forum - the code I give has the registry settings you need to use a 32kHz crystal to keep time…

http://www.ladyada.net/forums/viewtopic.php?f=22&t=4418&start=15

That link was very informative. I’ll try the 8MHz first, then the other when I’m feeling froggy.

Thanks you guys!