3 Replies Latest reply on Jan 14, 2018 5:15 AM by dche

    Design rule for guard sensor


      Hello together,


      i am planning to design a simple proximity sensor. Due to required liquid tolerance i want to use a guard sensor to have the best possible set up.


      But i cannot find any information about a guard sensor in PSOC4 descriptions. Only in the CY8CMBR3116 documentation the guard sensor is mentioned but without any design recommendations or layout hints. The CY3280-MBR3 Layout shows a Pin of the CY8CMBR3116 that is named with "guard", but no copper trace seems to be connected to the pin.


      Is there no guard sensor required or possible for PSOC4? If it is possible, can someone give me a hint how the sensor should look like on the PCB?


      Thanks a lot!

        • 1. Re: Design rule for guard sensor

          You can check AN92239 and CY8CKIT-024. This kit has required information on liquid tolerance with proximity sensor.


          The CY8CKIT-024 has two copper traces - One acts as a proximity sensors and the other loop can be connected to GND/Shield for water tolerance.

          Instead of connecting the outer loop to GND/Sheild, you can use this as a guard sensor to prevent any false trigger when large quantity of water is present on the touch surface.


          Guard sensor design depends on the actual board layout. For example, in your case, you want to be able to prevent false trigger when a water droplet falls on the sensor. So, you should have one loop inside the proximity sensor (to prevent any water moving from inside the loop to outside loop) and one loop outside the proximity sensor (to prevent any water moving from outside the loop to inside the loop) to act as guard sensor.



          • 2. Re: Design rule for guard sensor

            Hello Chethan,


            thanks for your quick help, i will use your advice in my design!


            I already worked with the CY8CKIT-024 in combination with -0024. There is no guard sensor mentioned, but a shield like you described it. Do in the CY8CMBR3116 datasheet it seems to me like there is a particular (or specific) pin for the guard sensor. Is that right or can i connect the guard sensor to any other pin?


            Anyway, when i activate the guard sensor in the CSD settings and go to the tuner, the guard sensor comes up like the touch buttons and the proximity sensor. Is there a possibility or need to tune the guard sensor in any way?


            Thank you!

            • 3. Re: Design rule for guard sensor

              In the MBR3 device the firmware is fixed and hence the sensor pins and guard sensor pins are fixed.


              For general PSoC 4 chip, any IO can act as a guard sensor. In fact, guard sensor is just another button sensor according to the CapSense component. The application code uses the ON/OFF status of guard sensor and rejects any false key touch on the regular sensors.


              Guard sensor has to be tuned in such a way that it does not get activated during a normal operation. For example, in your case, guard sensor should only be turned on when user touches it (Or a water droplet falls on it). It should never get activated due to proximity of the hand.