I want to measure the ac voltages using step down transformer do i input 5v directely to arduino?
Yes, you can apply voltages from 0 to 5V directly to an Arduino (unless it powered from 3.3V).
Please note that asking the same question in different parts of the forum is called CROSS-POSTING, and isn't allowed because it WASTES TIME.
Don't do it!
5vac will give higher than 5v to the pin as well as negative voltages.
Explain what you want to do and we may be able to help.
Weedpharma
Edit
The 0 to 5v mentioned above is for DC voltages. AC is another matter!
Weedpharma Thanks for reply
I want to calculate electrical power using ct and pt so as the step down pt giving me 5v ac therefore i have to input referenced voltages to the arduino please tell me that either i rectify it or i can input ac voltages directly into the analog pin?
Give more details of the full project. There may be a better way of doing it.
Give a circuit of how you are planning to connect the parts.
You cannot connect the 5vac direct to an input pin. Firstly the 5vac is RMS so the peak will be above the safe voltage for the input.
Secondly, the AC will have a negative swing so will destroy your Arduino.
Weedpharma
If i rectify the output voltages and use inverting amplifier for getting low referenced voltages than it will be ok for arduino?
Yes, rectify, filter, amplify, tweak, offset.... Can be done with varying levels of difficulty, performance and cost. I suggest you see if ACS712 current sensor will work for you.
I want to calculate electrical power using ct and pt
Everything you want to do is explained at this site, especially these links:
http://openenergymonitor.org/emon/buildingblocks/ct-sensors-interface
http://openenergymonitor.org/emon/buildingblocks/measuring-voltage-with-an-acac-power-adapter
or i can input ac voltages directly into the analog pin?
NO, you cannot. Don't do it.
You also need to consider the use of a "precision rectifier" circuit to eliminate forward voltage drops across your AC-to-DC rectifier. See http://sound.westhost.com/appnotes/an001.htm for an example of such a circuit
If I want to measure a 4.5 Vpp with 2.5 V offset, I can connect it directly to the arduino, wright?
As long as the P-P does not go above 4.5v, it should be ok.
Weedpharma