Different voltage requirements

Hello All,

Before I start connecting up various components to my Arduino UNO, if i Plug a 12V DC adapter to DC input of arduino.

Based on the following picture

On the left side power header,

-will I still read 3.3 V at the 3.3 PIN
-will I still read 5 V at the 5 PIN

And read 12V at the VIN pin?

Thanks

Yes.

Vin pin will read about .6vdc lower then actual external power input voltage due to a series polarity protection diode.

Pierre7:
Before I start connecting up various components to my Arduino UNO

You could also connect a multimeter...

Great news! Anyone knows the maximum wattage the VIN pin can take?

Pierre7:
Great news! Anyone knows the maximum wattage the VIN pin can take?

You probably want to read the section titled "Input Voltage" Limits and Recommendations on http://arduino.cc/en/Main/ArduinoBoardUno

So I guess 500ma would be the limit and should rely on voltage divider?

My apologies, I completely misread your question. I thought you asked "volts" not "watts." My bad.

From my testing I've found up to 12V you can draw up to 300mA through Vin on a R3, and 500mA on a R1.

Commonly we see people who report "my project works on USB but not with 12V." This is because 500mA is pushing the regulator too hot through Vin.

I estimated the on-board regulator, as laid out, could dissipate around 1W to 1.5W before shutting down, if I remember correctly.

[quote author=James C4S link=topic=229930.msg1659902#msg1659902 date=1396306927]
My apologies, I completely misread your question. I thought you asked "volts" not "watts." My bad.

From my testing I've found up to 12V you can draw up to 300mA through Vin on a R3, and 500mA on a R1.

Commonly we see people who report "my project works on USB but not with 12V." This is because 500mA is pushing the regulator too hot through Vin.

I estimated the on-board regulator, as laid out, could dissipate around 1W to 1.5W before shutting down, if I remember correctly.
[/quote]Cool! Thanks for the update