Frequency Hop Parameters
DO_NOT_REMOVE
Frequency hopping is a technique used in capacitive touch sensing to improve noise immunity by varying the acquisition frequency during sensor measurements. This helps avoid interference from external noise sources that may overlap with the acquisition frequency.
This section covers parameters that control Frequency Hop and Frequency Hop Autotune behavior (Noise Counter Measure modules).
DEF_FREQ_AUTOTUNE_ENABLE
Description: This parameter enables or disables the frequency hop auto-tune. Enabling the frequency hop autotuning feature allows the library to automatically replace the noisy frequency from the list of frequencies used for acquisition.
Range: 0 or 1
DEF_MEDIAN_FILTER_FREQUENCIES
Description: This points to the frequencies selected for the hop. There are 16 frequencies available for selection.
Range: FREQ_SEL_0 to FREQ_SEL_15
FREQ_AUTOTUNE_COUNT_IN
Description: This parameter acts as an integrator to confirm the noise on a measurement frequency.
Range: 1 to 255
More Info: The measurement frequency is changed only if noise levels are more than the maximum variance for tune-in count measurement cycles. Configuring a higher value for the tune-in count might take longer to replace a bad frequency. Configuring a lower value for the tune-in count might unnecessarily replace a good frequency.
FREQ_AUTOTUNE_MAX_VARIANCE
Description: This parameter sets the maximum variance for Frequency Hop Auto-tune.
Range: 1 to 255
More Info: When frequency hop autotune is enabled, the touch measurement frequencies are automatically changed based on noise levels. If the noise level is more than the threshold for the Tune in Count number of measurement cycles, then the noisy frequency will be replaced with another frequency. This value could be decided by analyzing the touch delta and should be set to less than the lowest touch delta. For effective operation, the touch delta across multiple sensors should be of the same range.
NUM_FREQ_STEPS
Description: This parameter defines the number of frequencies used in touch measurement. The designated frequencies will be utilized sequentially in a cyclical manner throughout the acquisition process.
Range: 3 to 7
More Info: If more frequencies are used, then the response time will be affected due to the median filter applied on the results obtained from these frequencies. If a higher number of frequencies is needed to tackle noise, consider enabling the Frequency Hop Autotune option.