3 Replies Latest reply on May 13, 2020 12:44 AM by MaMi_1205306

    Capacitive touch sensor


      I am designing a Capacitive touch sensor using Cypress CY8CMBR3102 IC. Circuit diagram is attached. The IC works properly. when any finger is touched to the pad, the LED glows and as soon as the finger is removed the LED goes off, That's perfect. But when the system is OFF and i keep the finger on the Touch Pad and then i switch ON the system, it does not detects the finger on startup, so i have to remove the finger and place it again, can anybody please let me know what changes have to be made in the circuit for the IC to detect the finger on Startup.

        • 1. Re: Capacitive touch sensor

          If you keep the finger on the Touch Pad and then switch on the system, it will not detect the finger.  The result is normal.

          Because the system is powered on by default without key triggering. More about the theory, you can refer to the MBR3 capsense design guide:https://www.cypress.com/file/46366/download

          • 2. Re: Capacitive touch sensor

            I agree with you.

            but this is one of the concept which i need to implement in one of my project. can you please suggest some thing better for this type of logics.

            • 3. Re: Capacitive touch sensor



              MBR3 series only sets the registers that don't use firmware.

              Furthermore, this device doesn't have a hardware reset.

              I think the only way to solve this issue is to use CapSense of PSoC and support it in firmware.

              For example,
              1. The device start with your finger on the sensor
              2. If you release your finger and touch the sensor again, it will not respond.


              Up to here is the current processing.

              3. If there is no finger signal from the sensor for a few minutes, Initialize the CapSense baseline.


              I think it can be avoided by configuring the above firmware.


              For battery applications,
              Suspend after a certain period of time,
              At that time, I think there is a way to initialize the baseline.

              However, it can't be avoided if the sensor is touched all the time even after startup.