5 Replies Latest reply on May 19, 2020 5:58 AM by MaMi_1205306

    CapSense raw count maximum

    taas_3144281

      Hi.

       

      My customer use CapSense.

       

      When my customer touch the CapSense button, raw count becomes maximum and I cannot understand the correct Signal.

       

      What could be the cause?

       

      Fsw:6000kHz

      Scan resolution : 12bit

      Modulator IDAC : 6 (auto - calibration

      Tuning mode : Manual

       

      Best Regards.

       

        • 1. Re: CapSense raw count maximum
          MaMi_1205306

          Hi,

           

          Looking at the waveform, I think that the capacitance of each sensor are different.

          So I think it is necessary to set the resolution and idac for each sensor.

           

          See page 67 below for tuning procedure.

          https://www.cypress.com/file/45441/download

           

          Simply put,

          If the resolution is 12 bits, adjust the IDAC so that the RAW count is 80% with no signal.

          Initial value : 12 bit is 4096, so about 4096 x 0.8 = 3200.

          If the SN ratio is 5 or more when touching the sensor with your finger, there is no problem.

           

          If the signal exceeds the maximum value,

          What is the current SN ratio?
          I think that the SN ratio has been secured sufficiently.
          In other words, I think that the resolution can be lowered.

           

          Regards,

          • 2. Re: CapSense raw count maximum
            taas_3144281

            Dear MaMi_1205306-san

             

            Thank you for your answer.

             

            The sensor may not work if IDAC auto-calibration is disabled and the IDAC value setting is changed.

            Do I need to consider anything other than rawCount when setting IDAC?

             

            Regards,

            Asanuma

            • 3. Re: CapSense raw count maximum
              MaMi_1205306

              Asanuma-san,

               

              Increasing the IDAC value will decrease the RAW count.
              Decreasing the IDAC value will increase the RAW count.

               

              When your finger is not touching the sensor,
              It should be 80% of the maximum resolution. ( Initial RAW connt up to (2^(n - 1) x 0.8 )
              Experience has shown that beyond this 80% value it will stop working.

               

              When the finger touches the sensor, it may tune beyond the maximum value.

              That is when you want to react even with gloves.
              Less increase in RAW count than fingers.
              Therefore, the maximum value may be exceeded when touched with a finger.

               

              In some cases, the sensitivity may be set lower to avoid hover action.

              In other words, the tuning depends on the specifications required.

               

              Regards,

               

              -- PS

              PSoC® 4 and PSoC 6 MCU CapSense® Design Guide - AN85951

              https://www.cypress.com/documentation/application-notes/an85951-psoc-4-and-psoc-6-mcu-capsense-design-guide

               

              "5.3.2 CSD Sensing Method" is described carefully

              For PSoC4 & PSoC6 CapSense are 85% of max resolution.

              Please read carefully.

              • 4. Re: CapSense raw count maximum
                taas_3144281

                Dear MaMi_1205306-san

                 

                Thank you for your answer.

                 

                Is there any way to reduce the sensitivity other than changing IDAC and Fsw?

                Also, is there a way to reduce the increase in raw count when there is a touch?

                 

                 

                Regards,

                Asanuma

                • 5. Re: CapSense raw count maximum
                  MaMi_1205306

                  Asanuma-san,

                   

                  The RAW count calculation formula is as follows.

                   

                  Single IDAC Sourcing mode:

                  Dual IDAC Sourcing mode:

                  - Increase the values of Imod and Icomp.

                  - Decrease the value of Vref, Fsw, and resolution.

                   

                  The RAW count is reduced by the above two points.

                   

                  When it comes to sensitivity,
                  I think the scanning speed and filters will also have an effect.

                   

                  Regards,