Zero-Crossing Detector

Discussion in 'General Electronics Chat' started by cheesemunger, Feb 15, 2009.

  1. cheesemunger

    Thread Starter Active Member

    Jan 25, 2009
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    I've been using http://www.andrewkilpatrick.org/blog/?page_id=445 and it says to convert an AC voltage to DC and then use a 4n25. But someone else says I can just use a H11AA1 straight away which would make sense. If that is true then that is gd:) but I don't have access to that , I have access to ILD620, is that fine?
     
  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    ILD620 should work. Limit the peak input current to ±40mA or less.
     
  3. cheesemunger

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    Jan 25, 2009
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    How do you suggest I do that?
     
  4. Ron H

    AAC Fanatic!

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    With a series resistor. Choose the value using Ohm's law: R=V/I.
     
  5. cheesemunger

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    Jan 25, 2009
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    so voltage is 240v and current is 60MA which is 0.06A. 240/0.06=4k
    so.... I could use a 4.7K 1/2W resistor? Or do I need 2 resistors in parallel to dissipate heat better?
     
  6. bertus

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  7. cheesemunger

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    Jan 25, 2009
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    Do I really have to you a capacitor? Can't I just use resistors? If I have to use a capacitor, does it matter what value?
     
  8. bertus

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    Hello,

    On the page I gave you is stated how to calculate the value.

    [​IMG]

    Greetings,
    Bertus
     
  9. cheesemunger

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    Jan 25, 2009
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    Wait, I'm not sure where I got my 0.06A from? LOL Where should I be getting it from?
     
  10. bertus

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    Hello,

    Ron H has said to limit the current for the ILD620 to 40 mA.
    I think the 60 mA was from the original schemaitc.

    Greetings,
    Bertus
     
  11. cheesemunger

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    Jan 25, 2009
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    On the website I posted to begin with he used 2x 47K 1/2W resistors in parallel, why can I not just use that?
     
  12. bertus

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    Hello,

    It depends on how many current you want to have on the led.
    In the origenal with 2X 47K there will be ca. 10 mA on the led.

    Greetings,
    Bertus
     
  13. cheesemunger

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    Jan 25, 2009
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    all its got to do it provide a high signal to a microprocessor (arduino) so 10mA should be fine.
     
  14. bertus

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    Hello,

    It is the current in the led, not the transistor.

    Greetings,
    Bertus
     
  15. eblc1388

    Senior Member

    Nov 28, 2008
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    Using a capacitor to provide voltage drop is common in many applications but not in this case where the aim is to detect the zero crossing of the AC voltage.

    Adding a capacitor in the detection path will inevitable shiftes the zero crossing point from the true zero crossing and makes the detection invalid.
     
  16. cheesemunger

    Thread Starter Active Member

    Jan 25, 2009
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    eblc1388: Thats what I though :p

    If you look later on in his post at his final schematic, he removes the led and just connects it to an input pin on a microcontroller.
     
  17. eblc1388

    Senior Member

    Nov 28, 2008
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    Which post? :confused:

    Where can I see the final schematic? Can you provide a link?

    There has been a recent thread about feeding AC voltage into a PIC pin via high value resistor to detect zero crossing. Doing so has other problems too.
     
  18. cheesemunger

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    Jan 25, 2009
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  19. eblc1388

    Senior Member

    Nov 28, 2008
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    I opened the pdf but still can't see what you meant. Sorry.:confused:

    Which input pin on the MCU are you referring to? Pin#22?
     
  20. cheesemunger

    Thread Starter Active Member

    Jan 25, 2009
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    look at Pin 21
     
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