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so, judging by this diagram ( http://www.arduino.cc/en/Hacking/Atmega168Hardware )of the pin-mappings for an atmega168, you should be able to remove the chip after burning it with the bootloader and a sketch for standalone operation, right? Simply connect inputs to corresponding pins on the chip, etc.?

You'd have to power it with a battery or some other power source (and I assume, regulate that power source to provide the correct voltage), and I suppose add resistors to compensate for the lack of the arduino's internal pull-up resistors, but it would work correctly otherwise, right?

Has anybody tried this? Maybe it's an obvious question.
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It should work fine.  One thing, though.  You'll also need a 16 MHz oscillator and supporting capacitors, unless you change the fuses on the chip (using a hardware programmer) to work on the internal oscillator.  
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Can the fuses be set and unset if needed ?
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Yep.  You can also continue to run the ATmega from its internal clock when it's on the Arduino board, if you don't want to have to change the fuses every time.
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It looks like the internal oscillator runs at 8mhz not 16mhz so timings maybe out !?
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It should be fine.  The LilyPad also runs at 8 MHz, so I've adjusted most of the core to work at either speed.  The PWM frequency will be different, but everything should work (and the delays should be correct).
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so I would connect an oscillator to the two pins marked 'crystal'? thanks so much for the help!
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Pretty much.  See the Diecimila schematic for details: http://www.arduino.cc/en/uploads/Main/Arduino-Diecimila-schematic.pdf
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I'm also in process of breadboarding around a pre-burned ATmega168.

Picked up a handful of 16 mHz resonators at Digi-Key earlier this week.  As I understand it, a couple of filter caps, a regulated supply, and the resonator is most of what I need to get a "naked" Arduino running.

(I'm tinkering on a project where I just don't have space for the full diecimila and shield).
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There is a page on the main site about using the controller by itself (with a few discreet components) on a breadboard

http://www.arduino.cc/en/Main/StandaloneAssembly
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Or you could check the Real Bare Bones Board:

http://www.moderndevice.com/RBBB.html

It think it will be hard, for a DIY project, to beat the 11$ pricetag and the ultra small footprint.

MikMo
http://www.mikmo.dk

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Quote
add resistors to compensate for the lack of the arduino's internal pull-up resistors
Unless I misunderstand you, what you refer to as "Arduino's internal pull-up resistors" are actually the "atmega168's internal pull-up resistors" so they are internal to chip and so "come along for the ride" when you make it stand-alone.

--Phil.
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