Hi all, I would like to ask for suggestions on how to measure the frequency from my main supply which is 240V? As i know the frequency varies very little, hence i would like to measure it as accurate as possible. The reason for this is because I'm doing a smart meter project with Arduino Mega 2560. I've researched and I saw people using LM2917 or comparator or AN795. However, I am not so sure on how to connect them from the main supply. As i know, I need to step down the voltage from 240V to 6V. I have no ideas after that. Suggestion are much appreciated. Thanks!