Energy Meter Project

I am building an Energy Meter with Arduino(Atmega328 bootloaded) as its core. As a first step to calculate instantaneous voltage,I am sampling the secondary voltage of a 3-0-3 stepdown transformer connected to mains in the primary.The problem is since tranformer secondary will not have a secondary ground I cannot connect it directly to Atmega328' ADC. And I wan't to reduce th output swing(8.48Vpp) further to acceptable limits (0 to 5V).Hope somobody can help me. I can provide more information if you want.

If you ground the centre tap and feed the other leads to two separate analog pins, you can check them separately.

A voltage divider will bring the voltage down. What is the peak to peak voltage out of the transformer?

its 3-0-3 so I suppose 12 * 1.414 = 16.97V if between 3 and 3.

Google on energy measurment ic.

There are custom ic which will savee you a lot of expense.

open energy monitor . org is a good library for energy monitoring.