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    new circuit design with Opto coupler

    Dear all,
    I am going to check a terminal block's voltage. There are 5 possibilities in voltage level.
    1.5V DC
    2.240V DC
    3.230V AC
    4.12V DC

    My scope is need to check the voltages levels and I should say what type of voltage is that... I can plan with opto-couplers and bridge rectifiers. problems is i cant differentiate voltage levels and type of voltage .. Suggestions are greatly accepted...

    Can i use optocoupler with 100K resistor in anode side to check both 5V and 240V DC? I mean will it sense both 5V and 240V Dc?

    •   Alt3rd July 2014, 15:12

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    Re: new circuit design with Opto coupler

    Short answer: no.

    5V (less the LED drop) across 100K would only give you about 30 microamps. Unless you have an optocoupler that can work with this low current, you'll need to find another method.

    I'm not sure what you mean by "My scope is need to check the voltages". If you are using a scope, what do you need optos and rectifiers for?



    •   Alt3rd July 2014, 16:20

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    Re: new circuit design with Opto coupler

    Quote Originally Posted by barry View Post
    Short answer: no.

    5V (less the LED drop) across 100K would only give you about 30 microamps. Unless you have an optocoupler that can work with this low current, you'll need to find another method.

    I'm not sure what you mean by "My scope is need to check the voltages". If you are using a scope, what do you need optos and rectifiers for?
    Dear Barry,
    Thanks for your reply... I am not using any scope. Ultimately I need to measure the voltage on terminal block using micros with help of other circuits such as opto coupler or other... Currently i am doing a project with control panel checking.. Its my first project with high voltage.. I need help...

    Thanks in advance



    •   Alt4th July 2014, 06:25

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    Re: new circuit design with Opto coupler

    Hi,

    Why don't you use a voltage devider and the ucontroller adc?

    Klaus



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    Re: new circuit design with Opto coupler

    All voltages can be "checked" by a set of voltage comparators. For AC 240V use a diode rectifier to get DC voltage output, and design suitable voltage dividers for each line.
    MAKE SURE ALL VOLTAGES HAVE COMMON GROUND!! Otherwise you can use optocouplers for 5 and 12VDC lines but for the high voltages use first the comparators with separate power supplies, then optocouplers.

    If the lines have separate grounds, the task becomes a safety issue. Start building comparators with each having its own power supply (e.g. a 9V battery), only then use their outputs to optcouplers.



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