2 Replies Latest reply on Aug 6, 2018 8:40 AM by erkec_1169106

    Liquid Tolerance when using spring coupling


      I am designing a capacitive touch keyboard using a PSOC4 4200L, the design requires using spring coupling to the overlay.

      As this design will be used outdoors we also need liquid tolerance, what is the best practice for the Guard electrode and shield electrode in this instance, do they need to be coupled to the overlay?


      Thanks in advance



        • 1. Re: Liquid Tolerance when using spring coupling

          Hello Erik,


          Shield hatch could be placed on the board, to minimize ground coupling of sensors. They need not be connected to the overlay.


          Guard electrode could be placed on the board and you need to include multiple springs on the board, connected to the overlay.

          Please make sure that only a water puddle would trigger the guard sensor and not a touch on CapSense sensors.


          You could also employ a firmware technique to reject touches, if multiple sensors are activated, instead of using a guard sensor.

          (If your application does not require multiple sensor touch at the same time)


          NOTE: Cp should be within datasheet limits. You can design a prototype and check if it meets your application requirements and then, go on with production.

          In general, you can refer to PSoC 4 CapSense design


          I hope this helps.


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          • 2. Re: Liquid Tolerance when using spring coupling

            Thanks Shanmathi, I will do as you have suggested