measuring 220V ac with MCU

Discussion in 'Embedded Systems and Microcontrollers' started by aamirali, Jul 11, 2014.

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  1. aamirali

    Thread Starter Member

    Feb 2, 2012
    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
  2. bertus


    Apr 5, 2008

    As senior member you should know that direct mains connected circuits are not allowed over here.

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