Pressure sensor 3.3V on 5V analog input (help need)

Projects Programming
1

Hello,
I would like to connect a pressure sensor (0-50kPa) which has 0-3.3V output on analog input port..
I'am using Arduino UNO board.

I'am confused with A/D converter..

I have found that is possible to set up arduino to use 3.3V as reference voltage so the digital value of 3.3V is 1024?

Or If I use default "setup" the analog value of 5V is 1024 so 3.3V is about 689..

what is right aproach?

in my case 0V represent 0 Kpa and 3.3V represent 50kPa..

Can someone help me to convert "digital" value into pressure?
(function is: Vout = VS (P x 0.018 + 0.04) ), VS = 3.3 V

for example:
digital value of 689 = 50Kpa and digital value of 0 is 0 Kpa...

thank you!

3

I wan't to use 3.3V as analog input.. so 3.3V will be 1024 (I will get better resolution)

On some web page I have read that I must connect 3.3V pint with AREF pin...but If I do that.. the board will not communicate over RS232 port..(I get exception that comm port does not exists)

image from the web

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