STM8T141 STMicroelectronics, STM8T141 Datasheet - Page 12

• Manufacturer Part Number: STM8T141
• Description: Single-channel capacitive sensor for touch or proximity detection with shielded sensing electrode
• Manufacturer: STMicroelectronics

STM8T processing
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STM8T processing
The STM8T141 device is designed to ensure reliable operation whatever the environment
and operating conditions. To achieve this high level of robustness, dedicated processing
have been implemented:
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Signal and reference calculation
Capacitive touch or proximity sensing is a technique based on detecting the electrode
capacitance change when someone is in proximity of the sensing electrode. The
capacitance change, induced by the presence of a finger or a hand in the device detection
area, is sensed by the variation in the number of charge transfer pulses composing the
burst. The charge transfer pulse number, also called “signal” is compared to a reference to
decide if there is a touch/proximity detection or not.
At power-up, a calibration sequence is performed to compute one reference value per
capacitive sensing channel. The reference is extracted from 32 burst measurements. Then,
the ECF takes care of its slow evolution over time.
To speed up the calibration process, the device is kept in normal mode whatever the low
power mode selected. The device operates in the selected low power mode when the
calibration process is completed.
Determining touch/proximity
The minimum difference between the reference and the signal necessary to report a
touch/proximity is the detection threshold (D
the mechanical switches, is applied to avoid noise induced detections.
Four different detection threshold settings are available and selectable by option byte. The
touch and sensitive touch levels are relative, which means the actual sensing distance is not
influenced by the Cs capacitor. The two thresholds should be able to adapt to various
surroundings and panel material or thickness. The proximity sensitivity thresholds are
absolute. This implies that the detection distance increases with the Cs capacitor. It provides
an easy way to tune the proximity sensing distance according to the application needs.
Signal and reference calculation
Determining touch/proximity
Self-calibration
Environmental compensation filter
Debounce filter
Doc ID 15699 Rev 7
Th
). A time filtering, similar to the debouncing of
STM8T141