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Sensitivity Tuning

Last modified by Microchip on 2026/03/20 13:55

Optimum Sensitivity

The purpose of this step is to optimize sensitivity for a light finger touch, as shown in the accompanying image.

Sensitivity for a light finger touch

Note: If the system is battery‑operated (such as a handheld device), you may notice reduced sensitivity compared to a mains‑powered system. To achieve consistent sensitivity in this case, you may need to adjust the sensitivity using isolated ground circuitry (for example, optocouplers).

Note:

  • We recommend using an analog gain of 1 for the best noise performance. Do not change if adequate sensitivity is achieved. Increasing analog gain reduces noise margin.
  • There is no advantage to having delta values higher than 50 counts. Consider reducing the gain to keep it under 50 counts.

Sensitivity Tuning With Gain

Keep the analog gain and digital gain as GAIN_1.

We always recommend keeping the analog gain at 1. Increasing the analog gain by one step will reduce the noise margin to half. Thus, increasing analog gain is recommended only for low-noise systems.

Observe the touch delta by gently touching the sensors. If the touch delta is >30, then use that gain setting. If not, go to Step 3.

​Increase the digital gain by 1 step and go to Step 1.

Ensure that ratio FILTER_LEVEL/D_GAIN >= 8. For example, if D_GAIN = GAIN_4, then the filter level should be at least FILTER_LEVEL_32.

Maximum digital gain should be limited to GAIN_8. Using more than that will reduce the Signal-to-Noise Ratio (SNR).

Warning

If the required gain is greater than 4, the touch sensor design is likely not optimal. Possible reasons include a sensor that is too small, excessive front panel thickness, or excessive ground loading. In such cases, we strongly recommend reviewing the sensor hardware design with reference to the capacitive touch sensor design guidelines. If tuning results in a gain equal to 4 and the system sensitivity is still low or marginal, consider applying the sensor layout optimizations described above.

The total gain in the system “analog gain * digital gain” must not exceed 8.

When both the analog and digital gains are set to GAIN_1, the calibrated signal value settles around 512 for devices using a 10-bit ADC in the touch library, and around 2048 for devices such as PIC32CM PL10 using a 12-bit ADC in the touch library.

Sample configuration in the touch.h file with digital gain shown as GAIN_2:

#define NODE_0_PARAMS{ X(1), Y(3), 0, NODE_RSEL_PRSC(RSEL_VAL_0, PRSC_DIV_SEL_1), NODE_GAIN(GAIN_1, GAIN_2), FILTER_LEVEL_16 }

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Sensitivity Tuning With Threshold

Monitor the touch delta value for each sensor.

Configure the threshold as 50~60% of the touch delta values.

Ensure that for light finger touch, the sensor goes into detect.

Adjust the sensitivity as required by performing a slight variation on the threshold.

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Tuning Sensitivity for Slider/Wheel/Surface

Monitor the touch delta value for each button on the slider/wheel/surface sensor.

Configure the threshold as 50~60% of the touch delta values for each button.

Ensure that for light finger touch, the sensor goes into detect.

Adjust the sensitivity as required by performing a slight variation on the threshold.

Move the finger throughout the sensor area and monitor the contact size on the Data Visualizer. Configure MIN_CONTACT value as 70% of the contact size observed on the Data Visualizer.

Perform minor adjustments on the MIN_CONTACT value and ensure that the position reported is smooth through the sensor.

Sample configuration in the touch.h file with MIN_CONTACT highlighted:

#define SCROLLER_0_PARAMS { SCROLLER_TYPE_SLIDER, 1, 3, SCR_RESOL_DEADBAND(RESOL_8_BIT, DB_10_PERCENT), 8, 20 }}}}

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