This type of module is used in applications where you want a simple way to detect that a piece of mains powered equipment is active. It can be used to detect if a load that has been turned on has actually activated. That allows automated fault detection and indication.
It could also be used to trigger functionality when a buildings lights are turned on or a pump runs.
For 120V use it may be useful to swap in a 1W-2W 33K-56K resistor to increase the optoisolator current.
As shown in the video, this building block is often used in multiples on elevator control PCBs for sensing phase presence and direction, to detect high voltage safety circuits and monitor loads to ensure they are powered when expected. Combining it on the main PCB saves on the cost of external phase monitoring modules.
Definitely use multiple high power resistors when doing this though. Even if it does take up a bit more valuable PCB space.
You can find these if you search for 220V optoisolator. They also do three and eight way versions.
They don't seem to do specific 120V versions, but these ones may work as is, or after the resistor mod. Cost for a single channel module seems to be around 4-5 space credits.
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12 thoughts on “120/240v to logic level optoisolator with schematic”
  1. Avataaar/Circle Created with python_avatars Mostafizar Rahman says:

    what's the model of this product? I am interested to buy it.

  2. Avataaar/Circle Created with python_avatars andres andreszz says:

    What about the speed of detection ? May I use it to activate a UPS, the time is under 10ms. ?

  3. Avataaar/Circle Created with python_avatars Markus Modaffari says:

    Hello Clive ,I am an Elevator / Escalator mechanic , I am trying to build a fault finder for older equipment that doesnt have controllers with fault finder/for intermittent stopping when I'm not present and fault latches but doesn't effect (jump)safety switch in a safety circuit-. optoisolator to aurdino — any idea's ,

  4. Avataaar/Circle Created with python_avatars Rich_Lex says:

    I had a whisker yesterday soldering a barrel jack. All good now.

  5. Avataaar/Circle Created with python_avatars Sam Horowitz says:

    Looks like a nice wet bird shite hit that last resistor spot on, and dripped down onto the lower resistors. =)

  6. Avataaar/Circle Created with python_avatars Κωνσταντίνος Κορωνιός says:

    Thank you for sharing your knowledge.

    I am wandering if there is a way to control one 200v device with an optoisolator and an arduino or an esp32. I want to control lights with hi frequency without the annoying relay's sound.

  7. Avataaar/Circle Created with python_avatars Steven Bliss says:

    The sensing time is AWFUL, simple RC calculation going to 3V from 240V puts it at 300mS+ or so, and being sine wave and the opto and LED current draws, more like 1+ secs!!!

  8. Avataaar/Circle Created with python_avatars Roy Tellason says:

    I suspect that the reason they're so casual about locating those mounting holes is that rather than using screws as you mention they're probably assuming the use of those plastic thingies that you find all over equipment these days, which would just push in, and not get all that close to the resistor…

  9. Avataaar/Circle Created with python_avatars Dr ZipZwan says:

    Excellent and very rich of infos as usually.
    I am trying to make a notification system, to get notified when 220V is available using that module.
    Anyone know please where I can get an arduino code for that module.
    Thx

  10. Avataaar/Circle Created with python_avatars Dinorko Dejaay says:

    podrias porfavor compartir el diagrama

  11. Avataaar/Circle Created with python_avatars zvotaï svfi says:

    Re : "Ghosting" what is the cause of this?? I have a space heater that does the same thing. Is this capacity between the power line all the way down the romex run? or leakage across the switch contacts or both?

  12. Avataaar/Circle Created with python_avatars Robert says:

    Nice video! 👍 Thank you in all you do!! For myself a retired Electronics Engineer in the past 8 years now and in the "past working in Electronics" from 1972 untill 2013….Iam getting back into Electronics again. It's in the blood!! Thanks for the refreshing videos.

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