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Connect the same Digital Input to two different optoisolator boards

nikoly

Hi, This is my first post and hope you can clear my doubts  I have about optoisolator boards!

 

I have 2 boards  which acquire singularly  and  correctly 12 v Contact as shown in the image belove :

image

Both boards work with singular connection without problem (first figure)

My problem  is that I want to make them working  with the same digital input  DI . So I decided to make this connection:

 

image

 

At first glance it seems to work because i can see both board make what they are designed for (like in the singular connection)  but I want to be  sure this connection cant give any problem in the future

 

Its important to note that the boards are different and in particular the value of the resistors are different so the total current will be splitted in two but with different amplitude.

 

From my point of view what its important  to consider is  that my power supply  can supply enough current (the total current ) for each board and that my contact can support the total current.

Could you please confirm me my theory ?

Hope you can help

Thanks in advance

  • 0

    Looks good to me.  Obviously you have the optoisolator LED grounds connected together and to the +12V ground.  As you say, the +12V supply must provide enough current for both optoisolator LEDs, and the switch must have a DC rating above the combined current.

     

    If you want to be creative, you could connect the optoisolator LEDs in series if they have the same current rating and you can separate the grounds.  Then you'd divide the current through the switch in half and only need a single resistor, cutting power used in half.  If they're different current ratings, you could add a parallel resistor across the lower-current LED so that it matches the higher-current LED.

  • 0 in reply to johnbeetem

    Thanks John for your answer!

     

    The right schematic is the attached one , I forgot to say that Board 1 is powered at 5V while the second one is powered at 12V , but both optoisolator have the same ground (each input ground of each input PCB connector are short to power supply 12V ground )

     

    The second one needs optoisolation (even if powered at 12V)  because I saw the PCB and I found a PIC18f46k20 which works from 1.8 to  3.6V and which (I suppose) is responsible for acquiring DI .

     

    I cant access the two optoisolator leds since they are part of manufactured PCB , only I can do is operate from 12V power supply to each Input PCB connector .

     

    Hope my theory is still valid after this information,

    Thanks again

    Attachments:
    imageopto2.docx