niner wrote:
Question 2 : How can I use AC to give the arduino high/low input? When main switch is on high, when off low? Like the sensors we use with DC?
Thanks
DON'T DO THAT
Please understand the difference between using and Arduino to control a 5V relay used as a switch for the mains AC (the two circuits are isolated, you may figure the Arduino pressing a button) and feeding 220V AC into the Arduino. You don't need to apologize for your English but you need to understand what we are telling you.
rockwallaby wrote:
If you are going to be playing around with AC as you mentioned, and if that is mains voltage AC, then you better get very clear about what you are wanting to achieve and how you will do this. Understand the risks involved with mains voltage or do not even attempt this if you have no skills or understanding.