Tuning of the thresholds

AN4316

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DocID024847 Rev 2

4.2.2

Linear and rotary touch sensors thresholds

For such type of sensors, the approach is different in the sense that these sensors are

composed of several channels. The standard test finger must be moved along the whole

sensor and a log of the delta must be recorded using STM Studio.

Detection thresholds adjustment

A rotary sensor log example is provided below:

Figure 6. Rotary sensor log

The worst case delta as shown in the figure above must be considered as the baseline to

compute the threshold for this sensor. This threshold must be reached in order to trig the

computation of the position and to report a detection on this sensor.

The same ratio used for a touchkey can be applied to this baseline, so between 65 % and

55 % to enter in detection and between 35 % and 45 % to stop reporting a detection.