2 Replies Latest reply on Jun 25, 2012 11:25 AM by user_14586677

    Error n connecting resistor

    naresh.vemishetty

      I am facing the problem in connecting the resistor  to the circuit ...i send the pic of the circuit and the error too...plz provide some information in how avoid that error.....

        • 1. Re: Error n connecting resistor
          user_1377889

          Since your resistors are external parts (as all annotation components are) you have to connect them via pins to the outer world.

             

           

             

          Bob

          • 2. Re: Error n connecting resistor
            user_14586677

            Are you trying to build a simple OpAmp summer ? If you don't need

               
               

            the hi Z afforded by the PGAs you can always eliminate them. And

               
               

            take your gain individulally for each channel by picking specific input

               
               

            resistors. Also offset the OpAmp so circuit works with - values.

               
               

             

               
               

                 http://www.ecircuitcenter.com/circuits/opsum/opsum.htm    

               
               

             

               
               

            Right now your circuit has a gain of - 1 in the OpAmp summer, referenced to ground,

               
               

            hence will not work, eg. output of OpAmp cannot swing below ground w/o you offsetting

               
               

            the NI input from something higher than Vss.

               
               

             

               
               

            Note dropping PGAs has the additional advantage of less offset and drift. If

               
               

            you still need super high Z inputs, have to use PGA, you still have to offset the

               
               

            OpAmp.

               
               

             

               
               

            Regards, Dana.