benireloop:
I have a question regarding the onboard DC/DC Converter on the Arduino.
What Arduino has an onboard DC-DC converter? The ones I have and know of use a linear regulator, very different.
If I draw 100mA of 5V from a 7805 regulator supplied with 12V, it will draw 100mA of 12V and drop 7V at 100mA straight to ground, the heat generated requires current to make.
If I draw 100mA of 5V from a DC-DC buck converter supplied with 12V, it will draw (100 x 5 / 12 + appx 5%)mA of 12V and make much less heat than the regulator, that appx 5% inefficiency x 100mA drawn.
I'm a fan of DC-DC converters but IMO you should put a bypass capacitor across the output PWR and GND contacts to help level the output at least if you use much power. Look into boost converters as well.