4 Replies Latest reply on Feb 5, 2019 12:23 AM by VasanthR_91

    SAR ADC – analog voltage _ Pioneer Kit -044

    CaHo_2689596

      If I apply a voltage via a potentiometer (V3.3 - GND) to P2_7, the voltage is converted correctly.

      However, if I put an amplified sensor voltage on the P2_7, the reference value (AVDD / 2 or internal 1.024 Volt) is always returned. Depending on which Vref is parameterized.

      I assume that it is a ground problem, but these ground are interconnected throughout.

      The voltage at P2_7 is between 0.1 - 0.8 volts (measured and depending on the gain).

       

      Thanks for your support.

        • 1. Re: SAR ADC – analog voltage _ Pioneer Kit -044
          MoTa_728816

          Hi,

           

          If the voltage read at the pin is (0.1~0.8), ADC should read some reasonable value.

          So I tired to reproduce your symptom.

           

          And when I set the ADC input pin as OpenDrain Driving High with the initial value as 1,

          the behavior looks like what you wrote.

          005-open_drain_drives_hi.JPG

           

          004-open_drain_drive_high_init_1.JPG

           

          Then when I returned the pin to High-impedance analog, no matter which the initial value is 0 or 1,

          the output seemed to be reasonable.

          007-TeraTerm-log.JPG

           

          At least accidentally setting pin type to OpenDrain Driving to High could be a reason.

          How about checking the pin type?

           

          moto

          • 2. Re: SAR ADC – analog voltage _ Pioneer Kit -044
            CaHo_2689596

            Hi moto

            thanks!

            I checked the pin settings again. The setting is in drive mode "high impedance analog".CY_analog_Pin.PNG

             

            The problem must be something else.

             

            carsten

            • 3. Re: SAR ADC – analog voltage _ Pioneer Kit -044
              MoTa_728816

              Dear Carsten-san,

               

              Thank you very much for your confirming the result!

              And I'm sorry my hypothesis was not correct.

               

              Beside the open-drain scenario, another reason I can think of is

              that the input voltage is always higher than the reference,

              but as you've already confirmed that this is not the case.

               

              It may not harm if you double check if the gnd of the amp and PSoC's VSSA is connected

              and measure the voltage between VSSA and P2_7 to make sure it's less than the reference.

               

              Although right now I have no usable idea,

              I'll let you know when I (can) come up with one.

               

              Meantime, it would be nice, if you can upload/attached a sample project which you and others can reproduce the symptom.

               

              Best Regards,

              30-Jan-2019

              Motoo Tanaka

              • 4. Re: SAR ADC – analog voltage _ Pioneer Kit -044
                VasanthR_91

                Hello Carsten,

                 

                Could you please attach your project ? In PSoC Creator ,  go to File -> Create Workspace Bundle -> Select minimal. Please attach the generated file.

                 

                Best Regards,
                Vasanth