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I had an Arduino UNO (ATmega168) standalone working, but I need more pins, and I decided to use the ATmega2560, I was searching for some schematics, and none of them shown an ATmega2560 standalone, only the full Arduino, with the FTDI, power transformers... etc integrated. So taking parts from those designs, I made this, but I don't know if it's enough or I need Something more: enter image description here

Note: VCC2 is connected to 5V.

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You need more decoupling capacitors - one per VCC and AVCC pin, plus a larger (10µF) for the whole chip.

You need a pullup resistor (and maybe button) on RESET.

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  • In theory (page 58 and 355 of the datasheet) the reset line has already a 30-60 kOhm pull-up resistor. Yes, it might not be enough in very noisy/humid/dirty environments (as I found sometimes). I also always put a 10kOhm: it does not harm. – next-hack Sep 4 '17 at 11:27
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    So it does. I'm used to MCUs with no internal pullup, but yes, it's good to add a proper external one anyway since that is quite a high value for a pullup. – Majenko Sep 4 '17 at 11:30
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    Especially if you plan to use an external DTR+100nF based reset circuit for programming - the lower pullup value will recharge the capacitor faster. – Majenko Sep 4 '17 at 11:33
  • Here in the Arduino forum: forum.arduino.cc/index.php?topic=152319.msg1143618#msg1143618 they say that just changing the processor, will be enough to work, basing on this: arduino.cc/en/Tutorial/ArduinoToBreadboard. – Arnyminer Z Sep 4 '17 at 14:21
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  1. check the datasheet;

  2. I would put a pull-up on the reset pin, plus a small capacitor;

  3. crystal + capacitors as optional;

  4. AVCC to VCC with filtering, if you need good analog performance;

  5. separate Vbat domain, if it has one.

...

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