ATmega 328p PCB

[mangekyo]

Hi,

I have been working on a hobby ATmega 328p custom PCB. There are some things I dont understand and am hoping I can get help with.

1. Do I need to enable the internal pull-up resistors for all the pins I am not using?
2. The schematic for Arduino nano suggest adding a 1k resistor for the TX pin and another 1k resistor for the RX pin. But the schematic for Arduino Pro Mini which also uses the ATmega 328 does not include these resistors. Are they needed?
3. I have read that i2c pins should have pull-up resistors. But this is not included in the nano schematic, but in the Pro Mini schematic, it says its optional. Are they needed?

[LarryD]

1 No

2 No

3 No

[gilshultz]

1. No
2. The resistors are to allow external device without cutting traces. If not used properly you could cause problems and possibly damage the Arduino or your pc.
3. Sounds like a good idea but not really, as you change I2C modules those values will change. You could use 4.7K with a jumper to enable them, that will give you the best of both worlds.