Thanks so much for both .
So I can use a simple voltage divider with 200kOhm resistor and 100kOhm resistor ( one side grounded ) i think . And across 100kOhm resistor I get about 3.5v if the transformer output LV side gives 12V AC ( and i assume i get about 10.5VDC after rectifying ) .
So 10.5V x ( 1/3 ) = 3.5VDC
So I can write the code to display 230VAC if the detected voltage is 3.5V at arduino analog input pins . Im I right sirs ?
Do I need to include any diodes to prevent damages to arduino ? or just only two resistors enough ?
And what if i use a smoothing capacitor inbetween the ground pin and the other side of the grounded resistor ( 100kOhm ) ?
And the other thing is lets say i arrange this voltage divider, and then i get the 3.5V to the analog input pin of the arduino . So I feel then the resistance of the circuit becomes parallel to the 100kOhm resistor I used . So the resistance becomes even smaller . So would this be a problem ? or is it negligible ?