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I am really despaired. I have spent a full day to understand this, and it seems that I still don't.

I have an Arduino UNO, with an ATMega328, for which I wrote a great piece of code.

Later, I have built a circuit on a bread board, where I want to use that same ATMega328, in a 3.3V configuration, and hence 8MHz oscillator .

So, I understood that I have to write a new boot loader to it (is that correct?)

So I follow many guides available, including the Arduino Standalone, and then I understood that I don't have another chip (ATMega328), in order to use the UNO as a boot loader.

So, I was trying to connect the ATMega328 directly from the bread board to the UNO's serial data, change the boards.txt file to add "ATMega on bread board 8MHz", and tried to boot-loading it, without success. I get the error that it can't connect with the board.

Now I have been told that I can't connect the ATMega328 directly to the UNO serial to boot load it, so my questions are:

  1. Do I really need to go over this hell in order to work with the same chip that worked with 16MHz, but now on 8MHz at 3.3V? (why in microchip I could just switch xtal? )
  2. If I do have to boot loading it, and I have one chip, and an UNO, how can I do that?
  3. How you do that in mass production?
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    More than a month passed since you posted this question, and there are two answers, below. Did any of them help you? Have you solved your issue? – Omer Jan 11 '15 at 12:40
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So do I understand you correctly that you want to lift the ATmega328 IC from the Uno board and use it on a breadboard? That strikes me as an unnecessarily risky proposition just to save a dollar or two for a separate ATmega328p.

Second, you technically might not have to write a new boot loader to the chip, if you don’t intend to reprogram it while it’s on the breadboard, but you definitely need different fuse settings, and the two changes are closely related in the Arduino IDE.

Third, bootloaders on ATmega are incapable of modifying themselves, so if you want to write a new bootloader, you always need a programmer (which can e.g. be your Arduino UNO running the ArduinoISP sketch or ScratchMonkey); I don’t think your single-microcontroller idea would work.

For mass production, you’d just use a programmer. Bootloaders tend not to be used for this, which can lead to situations like this year’s mishap at SparkFun

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There is a very nice tutorial by Adafruit, which explains how to get the Arduino Uno run at 3.3v, with minimum hussle and while keeping it's speed at 16Mhz, despite it's a bit out of specs (they claim it shouldn't pose a problem).

The main idea is to replace the voltage regulator and the fuse on the Uno board. This involves some soldering, but will probably give you the fastest results for prototyping.

I would not choose the Arduino Uno for mass production anyway, since there are plenty of Arduino compatible boards that runs at 3.3v (like Arduino Due, Lilypad, and Arduino Pro Mini to name a few. Full list can be found on Wikipedia). As a side note, for mass production, I would probably go with a custom made PCB, and not an off-the-shelf product, considering its high cost.

The link you provided explains how to recreate the Arduino around the Atmega328p on a breadboard. For that, you will need a USB to serial converter such as the suggested FT232, but please note that this tutorial does not address the issue on stake, which is running the chip at 3.3v (note the specs of the voltage regulator they offer, which is a 5v regulator).

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