kindly go through attached doc for automatic phase selector switch and I want to implement this project so for that I just want to know what will be the appx BOM cost for single PCBA????

 

Welcome to AAC.

I realize that you are seroius in asking this question, but it’s hard to believe. What you are asking is for someone to do an absurd amount of work. No one can answer this question for you. You will need to do the work required, possibly with the assistance of a PCB fab sales engineer—but it is unreasonable to ask people here to do this work.

 

what's the major advantage of designing automatic phase selector using microcontroller and optocoupler rather than comparator ICs and transistors????

 

Flexibility of using programmable device can allow one to adjust settings easily, for example device behavior in case of a phase loss, intermittent faults, or any other condition

 

if we deploy stepdown transformer 230v/12v AC, then if i/p is 250v AC then using same transformer (230/12v AC) transformer output of 250v AC is more than 12 v or it would be 12 v AC only irrespective of input AC voltage???? also, if i/p voltage is say 200v AC then also output of transformer will be 12 v only or less than 12 v as i/p v oltage is less than 230 v. kindly clarify