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Detect 220V signal — Parallax Forums

Detect 220V signal

TumblerTumbler Posts: 323
edited 2010-11-19 10:34 in General Discussion
Heys

I need to detect 220V AC signals, for logging with a BS.
My first attempt was using a resistor in serie with a optocoupler (led).
But i had to use a 2Watt resistor. Wich is too much.

So i came up with this idea.
220to5.jpg?w=6dd63c01
And my question is: is this gunna work?

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2010-11-15 11:36
    You can get small transformers designed for 220VAC input with output voltages in the 6V range. A diode, small filter capacitor, and maybe two resistors for a voltage divider are all you would need since the transformer would provide isolation.
  • TumblerTumbler Posts: 323
    edited 2010-11-15 20:59
    5 dollars for a transformer would be too expensive, just for logging a signal.

    Attached a schematic,
    but will this work?
    220to5.jpg
    572 x 413 - 129K
  • Mike GreenMike Green Posts: 23,101
    edited 2010-11-15 21:05
    That will work, but you will need a large enough resistor to dissipate the power needed. There will probably be somewhere between 2W and 5W depending on the amount of current for the Zener and the LED.
  • TumblerTumbler Posts: 323
    edited 2010-11-15 21:12
    Mike, seems that the 4N25 opto coupler led works at 1 mA.
    so i think i need 220K/0.25W resistor (R1)?
  • Peter KG6LSEPeter KG6LSE Posts: 1,383
    edited 2010-11-15 21:19
    neon bulb Pilot lamp coupled it to a CDS cell or photo diode/
    transistor as a HV in detector . Works wonders .
  • TonyWaiteTonyWaite Posts: 219
    edited 2010-11-16 02:34
    Hi,

    I'd go with Mike's transformer solution, overwhelmingly on grounds of safety.

    Certainly in my hands, it would be better to just have to guard the route from the Mains voltage to the transformer, with all components on the secondary side inherently safe.

    But then I always play safe with Mains voltages ... having experienced the occasional shock when taking shortcuts!

    Regards,

    T o n y
  • stamptrolstamptrol Posts: 1,731
    edited 2010-11-16 05:27
    Most AC input detectors use a capacitor in series with the opto coupler, rather than a resistor. The calculated Xc replaces the resistor with much less heat dissipation.
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2010-11-16 12:12
    Tumbler,

    Is this just to detect the presence of 220V or do you want any analog characteristics of the 220V?
  • Erik FriesenErik Friesen Posts: 1,071
    edited 2010-11-16 14:35
    The MID400 is designed for this http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MID400-ND

    If you want some response delay, use the cap, otherwise leave it out. I would use two or four resistors though, they have to dissipate a little. Very simple and reliable, at least for the 120v circuits I have been using them with.
  • MoskogMoskog Posts: 554
    edited 2010-11-16 22:31
    Tumbler
    Is it no way you can just find a power supply from something you don't use anymore (like a charger from a Nokia cellphone) that outputs just a few volts?

    I was into kinda similar problems when wanting to detect a compressor motor running or not. The easiest way was to connect to the coil side of the relay that runs by 12V DC and an optocoupler at the other end.
  • Peter KG6LSEPeter KG6LSE Posts: 1,383
    edited 2010-11-16 23:10
    most of the optoisolators I see are LV in HV switching out .

    with the NEON bulb Idea I was taking about youre using a normal Neon NE2 like bulb and letting its light activate a second device CDS Photodiode or Photo transistor .

    Neon bulbs rated at 220 AC are common in the industry and many are seialed so there safe to touch .
    Here is a 110V one http://www.radioshack.com/product/index.jsp?productId=3017351

    Forrest Mimms used a similar idea many moons ago with a LED and a soda straw and a LED like cased photo diode to make a custom Optoioslator
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2010-11-17 03:58
    I like the neon bulb idea. Cheap, low power consumption and small.
  • MoskogMoskog Posts: 554
    edited 2010-11-17 04:16
    For European customers Elfa sell things like that too..

    https://www.elfa.se/elfa3~eu_en/elfa/init.do?item=33-465-52&toc=0

    Not a bad idea, really.

    The only bad thing this bulbs only last for 3000 hours, 125 days.
  • TumblerTumbler Posts: 323
    edited 2010-11-19 10:34
    @Moskog, i need to monitor at least 30 automatic fuses (220v)
    I don't have room for 30 chargers :)

    @ Beau, just detect if the fuses on or off. And looking for the cheapest way. I think i will go for some resistors and a capacitor.
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