measuring 220V ac with MCU

[A 2]

I want to measure 220V ac with MCU.

Instead of using step down transformer, I want to use voltage divider of 1M & 3.3K.

So that 0V-220Vac gets reduced to  0V-0.724Vac.

 

Since it will also include negative peaks & MCU cannot measure negative values unless I put some offset to it.

So I have added 2.5Vdc offset.

 

Now I know that this can be done by opamp as an adder. But since I have -ve going peaks in ac voltage, so do I need to add -ve supply rail to opamp or opamp can add both volatges without using negative rails as one of voltage is going negative.?

 

 

 

1. Do I need negative rails?

2. What should be right opamp for this application?

3. Any reference schematic or any application node explaining measurement of 220V will be helpful

[Ashutosh Bhatt]

you dont need OP-AMP

you can use simple diode positive clamper circuit. it will shift complete wave to positive side.

[Author]

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