9 Replies Latest reply on Apr 2, 2020 11:31 PM by AH_96

    Response Time test of 4014

    mili_2550941

      Dear all:

           We use 4024 as a multi-Capacitive touch key processor. It generate an interrupt signal when touch down event be detected.Now we need check response time of our mass product.Can you tell me how to test ?

       

           There is a planstic cover on the touch key sensor which was connect to PCB by FPC.

       

      Thanks!

      Li Min

        • 1. Re: Response Time test of 4014
          AH_96

          Hi mili_2550941

           

          You can get a fair idea of the response time by the scan time parameter. Scan time is the time it takes to scan all the sensors in the system. You can calculate this by adding scan time of individual sensors. Scan time of individual sensors = (2^N - 1)/mod Clk Frequency. You can also check the scan time by checking the scan order tab in CapSense configurator GUI > Advaced settings > Scan Order tab.

           

          The actual response time depends on how often the CapSense_Scan is being called in the program. It also depends on whether a filter is enabled, if MFS is enabled etc but scan time is the main component. Enabling MFS increases scan time 3 times, so the response can simply be multiplied by 3.

           

          Please let us know if this answers your question.

           

          Thanks,

          Hari

          • 2. Re: Response Time test of 4014
            mili_2550941

            Dear Hari:

                 Thanks!

                 Sure we can calculate the total scan time as response time in theory, but for mass product we need check this item by a test method not by calculate.So any more good idea?

             

            Thanks!

            Li min

            • 3. Re: Response Time test of 4014
              AH_96

              Hi mili_2550941

               

              I am assuming that the response time meant here is the time between the finger touching the sensor and the time the uC returns widget ON status. To do so, there needs to be some mechanical arrangement to detect when the finger is placed on the sensor. We do not have a recommendation as to what this could be.

              If you have an arrangement to detect the exact time the finger is placed, a simple timer block can be used or a GPIO can be toggled to measure the time.

               

              To calculate the worst case response time (this again is a calculation and not a physical measurement) you can measure the loop time (the time between each scan) and multiply by the debounce set in the component. This would give a fair idea as to what the response would be, but again, this is not a measured value.

               

              Thanks,

              Hari

              • 4. Re: Response Time test of 4014
                mili_2550941

                Dear Hari:

                     Yes, the response time which we test is same as CTP's TRESP(The time between a finger touchdown event on the touchscreen and the touchscreen controller generating an interrupt signal).

                     We have a interrupt output when 4024 detect a valid touch down.

                 

                Below is our simple test method:

                1:Use a conductive tape on touch key,and connect it to o-scope CH1

                2:Connect o-scope CH2 to 4024 interrupt output.

                3:touch the key use finger,calaulate the time difference.

                But the result is not stable.So we ask for some advice to improve our test accuracy.

                 

                By the way,we also use cypress CTP process IC,so can we use the same method which used to test response time of CTP?

                 

                Thanks!

                Li min

                • 5. Re: Response Time test of 4014
                  AH_96

                  Hi mili_2550941

                   

                  A slight variation is expected in the result as the sensor might be touched during an ongoing scan/immediately at the beginning of a scan. Hence there will always be a tolerance which is dictated by the scan time+loop time. The best result that you obtain (minimum time) will be when the sensor is touched exactly before a scan is initiated.

                  The maximum time will be when the sensor is touched during an ongoing scan - in this case, the uC has to wait till the next scan is completed before providing the result.

                  In practice, a response time of 20ms is considered good for the sensor.

                   

                  Please let me know the MPN of the IC that is used in CTP.

                   

                  Thanks,

                  Hari

                  • 6. Re: Response Time test of 4014
                    mili_2550941

                    Hi Hari:

                         Touched during an ongoing scan/immediately at the beginning of a scan may cause a time difference,but should be less.Our test result is 2xms~16xms,it's too big.

                         CY-AT81688-100AS61 for CTP.

                     

                    Our CTP supplyer provide below test method for CTP response test,can we use it for 4024?

                    1:

                    2:

                    3:

                    4:

                    5:

                    Thanks!

                    Li min

                    • 7. Re: Response Time test of 4014
                      AH_96

                      Hi mili_2550941

                       

                      Yes, a test similar to one described can be performed to find response time.

                      Can you please modify the code to have a pin toggle just before CapSense_ScanAllWidgets()? This would help us estimate the loop time.

                       

                      Another test is to enable tuner (multiple code examples present) and use the metal finger ungrounded to make sure the sensors are not triggered; and the metal finger grounded to make sure sensors are triggered. It could be that even grounded, the raw counts are not increasing above finger threshold in some cases. This will help us rule out the error in the metal finger.

                       

                      Thanks,

                      Hari

                      • 8. Re: Response Time test of 4014
                        mili_2550941

                        Hi Hari:

                             We can't modify the code because of mass product.

                             We want use metal finger test this item.We can read out the row data & base line data though BCP when testing,we can share this data and method for everyone.

                         

                        Thanks!

                        Li min

                        • 9. Re: Response Time test of 4014
                          AH_96

                          Hi mili_2550941

                           

                          This would give us the sensor status, and from the observation it does seem like the sensors are getting triggered. However, the issue is regarding the timing. BCP will not be able to provide this data. However, one thing that you can do is to probe the sensor with as oscilloscope and measure the time between the start of a scan and the start of next scan.

                          This wont require code modification.

                           

                          Please note that only one sensor must be probed.

                           

                          Thanks,

                          Hari