'Additional' components in Arduino Uno schematic

Hi all, I'm building another arduino compatible board. I'm working partly from the UNO schematics this time and I have noticed a few components that I haven't used before when building quick boards or when using the 328P on a breadboard. I guess they must have been included for a reason, but is it worth including some / any / all of them?

  • R2 - 1M resistor between the XTAL pins?
  • C6 - 100n cap between vcc and gnd?
  • D2 - diode between rst and 5v?
  • C4 - 100n between AREF and gnd

Thanks

dtokez: Hi all, I'm building another arduino compatible board. I'm working partly from the UNO schematics this time and I have noticed a few components that I haven't used before when building quick boards or when using the 328P on a breadboard. I guess they must have been included for a reason, but is it worth including some / any / all of them?

  • R2 - 1M resistor between the XTAL pins? I think this is for better starting support for a 3 terminal ceramic resonator that Uno ships with these days, not needed if your using a two terminal crystal resonator.
  • C6 - 100n cap between vcc and gnd? Such bypass caps mounted close to all the +5vdc power voltage inputs to the AVR chip are always a good practice.
  • D2 - diode between rst and 5v? If you using the arduino DTR auto-reset function through a series .1 cap to the reset pin, then this diode from reset to Vcc solves a nasty intermittent lock-up symptom that can rear it's ugly head.
  • C4 - 100n between AREF and gnd Yes, if your using the analog input pins with analogRead commands, this will help with noise floor of ADC. Lefty [/list]

Thanks

Thanks very much lefty, that is exactly the info I was looking for :)