AC(grid) dectection method.

Discussion in 'General Electronics Chat' started by ak52, Oct 25, 2014.

  1. ak52

    Thread Starter Member

    Oct 15, 2014
    145
    4
    Hello Everyone,
    In continuation with this thread:
    http://forum.allaboutcircuits.com/threads/suitable-opamp-for-very-low-signal-amplifications.102442/

    I am next exploring the possible efficient ways to detect grid voltage using a micro-controller(dsPIC33):

    1.I use a step down transformer ,then give it to a rectifier ,filter the signal, and then give it to micro-controller as a digital input.
    Using a transformer gives me isolation from line side and user(MCU) side.

    OR

    2.I simply use a voltage divider and give it to as ADC input of my MCU.
    Not using a transformer saves a lot of cost and makes the circuit lighter and portable,but i sacrifice isolation.

    If you have any other suggestions,I'd be glad to hear them.
    Arun
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,006
    3,232
    It depends upon what do you want to do with the measurement results?
     
  3. ak52

    Thread Starter Member

    Oct 15, 2014
    145
    4
    As of now i have not planned to do any thing fancy yet.I need the MCU to know/detect that grid voltage is present.

    If it is read as a digital input only ,it would trigger charging a battery partially though grid supply.
    If it is read via an ADC, i could also check for AC voltage limit protections(over-voltage ,under-voltage,voltage fluctuations,spikes,sags,swells etc.)
     
  4. #12

    Expert

    Nov 30, 2010
    16,283
    6,795
    And then there is the diode input protection scheme...
     
  5. ak52

    Thread Starter Member

    Oct 15, 2014
    145
    4
    Hello #12,
    I normally use the two schottky diodes,one grounded the other pulled up to Vcc at opamp outputs before the signal is given into the MCU.
     
  6. #12

    Expert

    Nov 30, 2010
    16,283
    6,795
    I guess I misunderstood what you needed. Talk about surges on the 50 amp detector resistor told me you needed to protect the inputs of the op-amp. Oh well. No harm done.
     
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
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    I recently wanted to log the presence or absence of 240Vac into an Arduino. I wanted complete galvanic isolation from the line for safety. I thought about various transformer and opto-isolator schemes, looked in the junk box, and came up with one of the these:

    [​IMG]

    Can be bought at a thrift shop for $0.50. Complete isolation. 100 to 250Vac input. 5.0V output. Draws only mA from the AC line if output is lightly loaded... Interfaces directly to a 5Vcc Arduino input port pin. What is not to like?
     
  8. Externet

    AAC Fanatic!

    Nov 29, 2005
    759
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    Why not a mains powered relay; its contacts closing will signal the microcontroller mains is present.
    Or a mains powered optocoupler. (as in a telephone ringing detector) - Will do the same.
     
  9. ak52

    Thread Starter Member

    Oct 15, 2014
    145
    4
    Are you referring to a USB charger? 230 VAC to 5Vdc.
    That was indeed my first idea which i posted in the first post,common adapters consists of a small low current transformer,coupled with a bridge rectifier and a regulator.
    Good thing about the above is that it comes as a single unit so no hassle of selecting the components ,,):)
    Yes i am looking into relays also,searching for one at the moment.Can you suggest me the optocoupler part number that i can look up.
     
  10. Externet

    AAC Fanatic!

    Nov 29, 2005
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  11. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    I say again:

     
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