18 Replies Latest reply on Apr 1, 2019 11:14 PM by colporteur

    Opto-isolotor module implementation suggestion(s)

    colporteur

      G'Day,

      How can the following opto-isolator circuit output be used?

       

      I purchased (on sale) a number of 4 channel opto-isolator modules from a Asian manufacture. I made the buy without due diligence on my part. The circuit works but there doesn't appear to be a way to use the existing connection as an output to do work.

       

      817

       

      There are four physical connection points on terminal strips. IN1 & G on the left are two physical connection points and V1 & G are the other two physical connections shown on the right. Assuming IN1 & G on left are input and V1&G on right are output, there doesn't appear to be a connection point on the output to do actual work.

       

      In my haste to purchase such a great sales deal, I failed to realize there is no external connection on the south side of the 3K resistor. If V1 is supply and G is ground, then where is the output connection?

       

      I do have a few electronic marbles rolling around in my head from post secondary education. That knowledge provides me no solution to how I get output from this circuit to do work without adding an additional physical connection. That is hard given the board uses surfaces mount components and very little space to make solder connections. I did make a connection to the south side of the resistor to test operation and it worked.

       

      If someone has a suggestion on how to use the circuit without modification, I would appreciate it. Other wise the great sales deal was a bust.

       

      Sean

       

      options

      • Reply
        • Re: Opto-isolotor module implementation suggestion(s)
          geralds

          what do you like to pay for my development support?

           

          1. What does the opto output drive? Is this a logical or analog input of the following circuit?

          2. how high is the voltage?

          3. do you really need to use the emitter follower?

           

          "south side", "north side" .... is a funny language (of course it exist this slang).

           

          This "jumper cap" can be really a problem, if you like to nail that input directly to GND, one for the opto, one for the circuit.

          I think this is a "switch off" for the following circuit.

          But here, I think, is needing more than just nailing with a jumper.

           

          A bit more information would help thinking better with your idea.

          I have some solutions for you.

           

          Best Regards

          Gerald

          ---

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            • Re: Opto-isolotor module implementation suggestion(s)
              colporteur

              G'Day,

              Much appreciate your feedback. Compensation for your initial response is in the high zero's. You can have as many zero's as you feel are necessary to compensate you for any future time you invest in development support.

               

              I am not looking at the opto-isolator as a driver but rather an output logic producer, whether that be high or low when the input is triggered. I didn't see the voltage as being important but if that garners a result then +5V be the value for input and output. I have no preference on how the output is generated (i.e. emitter follower).

               

              I elected to use South side and North side reference to minimize my effort and maybe appeal to a wider audience. The drawing is a cut&paste from the manufacture docs. Ideally it would have more detail. I updated the drawing in Inkscape to improve the notation. I made the navigation assumption most maps providing direction have a indicator of North facing the top.

               

              The "jumper cap" is not a capacitor but rather a jumper that enables use of an external ground (jumper removed) or use the same ground (jumper installed) provided from the input. You would assume the abbreviation cap means capacitor but not in this schematic.

               

              This is a commercial module still being sold. My knowledge suggests there is a design flaw (i.e. no output connection). I am challenging that notion by asking a wider audience. With a solution forthcoming I am hoping the sale item I took advantage of actually has some value.

               

              Sean

              1 of 1 people found this helpful
            • Re: Opto-isolotor module implementation suggestion(s)
              ralphjy

              How did you come up with that schematic?  It would be helpful if you labeled the pin numbers on the optocoupler..  Pictures of the board (both sides) would also be helpful.

              1 of 1 people found this helpful
                • Re: Opto-isolotor module implementation suggestion(s)
                  colporteur

                  The schematic is manufacture provided. I have done some some drawing notation to clarify the resistor and the manufacture cap notation.

                   

                  I confess, it is not uncommon for me to provide an insufficient detail response to technical questions. I challenge that response in this case. I appreciate your feedback but in my opinion, the details you ask for contribute little to determining if there is a practical use. If all the pins were labelled, the 817 opto-isolator box fully drawn, the voltage references provided and a full printed circuit board layout provided, I don't see how that would arrive at a solution.

                   

                  I don't want to modify the board. I don't want to add components to the board. The circuit works.   WORKS, in the sense that the 817 behaves the way it should when a signal is applied. The box is an generic 817 opto-coupler. A signal on the input triggers a response on the output. The question remains how is the output provided obtained given the limited connections.

                   

                  Sean

                  1 of 1 people found this helpful
                • Re: Opto-isolotor module implementation suggestion(s)
                  dougw

                  The output is V1 - it should not be connected to a power supply although a power supply won't hurt it.

                  It should be connected to an input that is pulled high externally. However, the current that the opto-coupler can sink is limited by the 3K resistor. If you want a logic output, the external pullup might be around 47K.

                  Inside the optocoupler is a phototransistor that turns on when an input is applied.

                  • Re: Opto-isolotor module implementation suggestion(s)
                    colporteur

                    If I am reading the two suggestion correctly, I can draw output from either the emitter or the collector if the 817. I have drawn a schematic of the two options. Would 10K values for the output resistors be acceptable to produce a logic output?

                     

                    Sean

                      • Re: Opto-isolotor module implementation suggestion(s)
                        dougw

                        It all depends what you are driving. It would create a swing of roughly 60 % of the supply voltage - a bit marginal for CMOS.

                        If you are driving an LED, no resistor is needed, just connect it directly between either pin and the appropriate rail.

                        Likewise driving a bipolar transistor would work fine and doesn't require an external pullup, although the new transistor might need one.

                      • Re: Opto-isolotor module implementation suggestion(s)
                        colporteur

                        A heart felt thank you, to all those who contributed to this discussion. I gained considerable technology knowledge through our interaction. The dialog also gave me insights into how best to present questions in the forum.

                         

                        Unfortunately, making use of the modules containing the circuit was a bust. I had hoped to use the modules as either an input or an output interface for a Raspberry Pi. During testing the 3V output of Pi GPIO's was not sufficient to saturate the opto-isolator input.

                         

                        I have an alternate solution in place, that was discussed in a Grab Bag RoadTest review I just completed. Thanks again for your help.

                         

                        Sean