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220v power interface diagram

220V Power Line Interface

This simple 220V power interface is intended as an interface for monitoring electric equipments and devices using a computer. The interface only senses whether the device being monitored is turned on or off. The most important aspect of the circuit is the galvanic isolation between the AC main line being monitored and the interface to the computer. This is done with the use of the optocoupler IC TIL111 but a suitable replacement can be used too.

Main power live interface circuit diagram

220v power interface diagram

To avoid having to modify the circuit for each device being monitored, the circuit monitors the device’s AC power line directly. The resistor R1 lets a current of around 0.5 mA through the optocoupler LED. The other half of the current is rectified through the diode D1. It is obvious that the current to the optocoupler LED is half wave rectified. This means that the phototransistor part of the optocoupler receives only light impulses of around 100uA. The capacitor C1 filters out the current pulsation and maintains a smooth output current. In case the current pulsation is needed, just remove C1.

42 Comments

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  • scottawildcatgmail-com

    I am wanting to use the transistor circuit posted by Mihai on October 6, to sense water level. I will only be sensing 12VAC from the CT on a power transformer. Do I still need the opto coupler to isolate the AC from the DC portions of the circuit or could I just use a transistor in it’s place? If so, what would be a good transistor to use?

    • Mihai

      Hello!
      It’s not clear what you are trying to do. Be more specific. Maybe if you post a schematic we can help you.

  • Raja

    I would like to know ultimately the original circuit is working? any one tried and satisfied?

  • mars

    got it working was a bad connection in the breadboard

    thanks again

  • Viktor

    Hi,
    I have built this one… and it works fine for me so far…

  • mars

    HI
    thanks for the circuit i have built the bottom one on a breadboard to test but cant seem to get it working no 5volt on the output
    is there mabe someone that has built this circuit and it is working

    thanks

    • Mihai

      There must be a mistake somewhere. It must work. Check again the wiring. Check each component. Measure the collector of optoc. (to GND) voltage.
      Put a LED in antiparallel with IR diode of the optoc. See if it is lit when connected to power line. See the new picture.

      Good luck!

  • mars

    hi

    can you post a similar circuit that switches high when the 220Vac is applied

    thanks

  • Juan

    Hi

    I purchased the transitor but they gave me a replacement “A733” and looking the datasheet it doesn’t look similar.

    So, can I use a 2N3704?

    Thanks!

    • Juan

      I have just built it so I wanted to write a feedback

      I used for T1 a 2N3904 (I typed wrong before sorry) and a 5,6kΩ resistor in series as you said.

      It seems to work perfect, I get 0,1v when 220VAC is connected and 5v when disconnected.

      Thanks a lot again!

    • Juan

      Ok, thanks a lot for the reply!

    • Mihai

      YES, 2N3704 is a good choice. Don’t forget to insert a 4.7kΩ(1k…10k) resistor in series with collector of the phototransistor(in optocoupler), otherwise the output phototransistor may overheat.

      Good luck!

  • Viktor

    boris.free@mail.ru

    You may use this address to contact me. Thanks a lot so far for your support.

  • Viktor

    I saw lots of similar circuits but those are have big PCB sizes, so I need as much small PCB size as possible.

  • Viktor

    Thanks for the answers.
    I nee do have such a “detector device” which can give me the (+5) logic HIGH level signal when the 220 V AC power applies to the input, just “opposite” functionality as presented here. I want to have it in my ventilation fan control circuit. So, this should work in pair with wall lighting switch… when light is ON – then I need to have the logic HIGH signal somehow. I appreciate any helpful info, thanks.

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