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MSP430FR2633: Regarding touchpad tuning RX/TX resolution

Part Number: MSP430FR2633

Hi,

My customer is adjusting the RX/TX resolution of the touchpad with the CapTIvate Design Center GUI. I have two questions about this.

Q1) "Desired Resolution X Axis" and "Desired Resolution Y Axis" are described as "The desired resolution may be set from 2 to 65535" in the explanation on the right of the GUI, but they can only be set up to 65534. Is the GUI working correctly?

Q2) They assume a resolution of 0-127, so when they set these values to 128, they now return values in the range 0-125.
Perhaps the range is corrected so that the ones place is 0 or 5. (Because setting the resolution to 9 returns a value of 0-5)
Is it possible to achieve a resolution of 0-127?

Their evaluation environment

  • GUI version : 1_83_00_08
  • Setting value other than the corresponding parameter
    • Prameters of tuning tab
      • Thouch Threshold: 20(Set All)
      • Rejection Threshold: 30
      • Upper trim X(Y) Axis: Same value as Desired Resolution X(Y) Axis
    • Pin setting
      • 6x6 pad pattern

Best regards,
Sasaki

  • Hello Sasaki-san,

    Regarding your Q1 - I believe this is a bug, but in practice you don't really want to use a resolution as high as 65534.   I'm  working on getting this changed in the GUI so it limits the resolution to 8191.  Every touchpad design I have been involved in, using 1024 as the resolution is more than enough to achieve the desired accuracy.

    Regarding Q2 - Although the GUI allows the resolution to be set within the range from 2 to 65535, I suggest that the resolution be set at a minimum 2x as large as the number of points of interest, but from all my experience 1024 works good for all touchpad applications. For example, if the customer wants 128 points (0 to 127) in both X and Y directions set the measurement resolution to 1024  then shift the resulting X and Y position by 8 (shift value right x 3).  Example ->  X and Y resolution set = 1024.  When finger touched in middle of touchpad X = 511 and Y = 511.  To scale to customer's desired range, shift the measured values by 3 as shown here:

    Xresult = (Xmeasured >> 3)  which is  511 >> 3 = 63. 

    The reason for using a higher resolution is to provide better position accuracy. 

    The customer also must keep in mind that the perimeter of the touchpad becomes non-linear as the sensitivity drops off.  Because of this it becomes difficult to achieve a '0' on X-axis with finger all the way on left and '1023' when finger all the way on right.  So, this is where the upper and lower trims help.  To explain how these work, refer the customer to the Captivate technology guide, workshop chapter - Tuning a Slider section.  The process to trim the endpoints on a one-dimensional slider is exactly the same as is done for the touchpad.  If done correctly, the customer will be able to achieve X and Y positions from 0 to 1023.

  • Hi Dennis-san,

    Thank you for your the detailed explanation.

    The problem is clear. I will contact the customer with this.

    Best regard,
    Sasaki

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