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TSC2013-Q1: Better Sensitivity

Part Number: TSC2013-Q1

[ TSC2013-Q1 ] Better Sensitivity

Hi,

Do you have any ideas that allow TSC2013-Q1 achieve better sensitivity?
The "better sensitivity" means that the touch feeling is like capacitive touch.

As far as I check the datasheet, there is no direct register that defines the sensitivity, however, we have several time-related registers such as stabilization-time and delay time. If we minimize these time, do you think we can achieve better sensitivity?








I understand that it's a trade off between better sensitivity and invalid operation. If we make sensitivity more sensitive, the system might detect unintended vibration as touch. However, it's appreciated if you have general guidelines and share with us.

Thanks,
Ken

  • Hi,

    Can anyone support this query from my customer?

    Thanks,
    Ken
  • Kenichiro,

     

    Sorry for the delay.  Below are my thoughts on improving the sensitivity based on data sheet excerpts.

     

    Page 17: The data sheet excerpt below agrees with you thought that the delay can be used to improve the sensitivity. Based on this I expect that too short of a delay would product unpredictable results from bouncing. I believe that too long of a delay would potentially miss touch events. The sensitivity will be different for different panels, so you will have to empirically tune for the optimal value.

     

    When touching or pressing the touch panel with the drivers to the panel turned on, the voltage across the touch panel often overshoots and then slowly settles down (decays) to a stable DC value. This effect is a result of mechanical bouncing caused by vibration of the top-layer sheet of the touch panel when pressing the panel. Without accounting for this settling time, the converted value is in error. Therefore, introducing a delay between the time the driver for a particular measurement is turned on and the time a measurement is made is necessary.

     

    Page 18 & 21: A analog (RC) filter may be required to minimize noise pick-up. In this case, you may need additional settling time to account for the filter group delay. Take care to keep the capacitor value in the filter small to minimize the delay times.

     

    In some applications, external capacitors may be required across the touch screen for filtering noise picked up by the touch screen (such as noise generated by the LCD panel or back-light circuitry). The value of these capacitors provides a low-pass filter to reduce noise, but causes an additional settling-time requirement when the panel is touched.

     

    This configuration underscores the need to use the minimum possible capacitor values on the touch-screen inputs. Capacitors can be used to reduce noise, but capacitors with too large a value increase the required precharge and sense times, as well as the panel voltage-stabilization time.

     

    Page 21: You can use a preprocessing digital filter to minimize noise. This can be a median value filter or an averaging filter or a combination of the two. I would try to minimize noise using the digital filter before using an external capacitor. A combination of the digital filter and delay should give good sensitivity for your touch screen, and these settings should be empirically determined.

     

    If the acquired signal source is noisy because of the digital switching circuit, evaluating the data without noise may be necessary. In this case, the median value filter (MVF) operation helps to discard noise. The first action is sorting the array of N converted results. The return value is either the middle (median value) of an array of M converted results, or the average value of a window size of W of converted results:

    N = the total number of converted results used by the MAV filter

    M = the median value filter size programmed

    W = the averaging window size programmed

     

    Thanks,

  • Hi Art,

    Thank you for sharing your ideas, it's helpful!

    I have an EVM with me and tried to change PV[2:0] to shorter value with Aardvark, but failed.
    (I know that MPS430 on EMV feeds the default setting with PV[2:0] = 011 (1mS)).

    Anyway, I will consult with my customer. I will come back to you, if necessary.
    Thanks,
    Ken