I found this tutorial for building your own arduino on a breadboard.
I'm planning to do that on a PCB and also power the the processor with 12V DC.
The thing is, where should I connect the power jack ?
I would connect it to either pin 7 or 20 but not sure what the difference is between Vcc and AVcc
And also how can I reach to 5V output ? Is it also introduced through voltage divider on the arduino board ?
power the the processor with 12V DC.
+12 anode of 1N4007 cathode to 7805 regulator input, 7805 regulator output is +5V.
Of course you will power the 7805 with 12V and feed the o/p of the 7805 to the processor VCC(7) and AVcc(20) .
Aref(21) to 100nf to ground.
VCC(7) to 100nF to ground.
AVcc(20) to 100nF to ground.
5V and -only- 5V connects to both Vcc and AVcc. Do NOT connect 12V to those pins. It should go to ground and the input of the 7805, seen here:
That page is flawed - there should be several 0.1uF bypass caps across both power rails, one right at AVcc, and on ARef.