STM8T143 STMicroelectronics, STM8T143 Datasheet - Page 24

• Manufacturer Part Number: STM8T143
• Description: Single-channel capacitive sensor for touch and proximity detection
• Manufacturer: STMicroelectronics

STM8T143 processing
5.5.3
Figure 14. Unwanted detection managed by the reference freeze timeout
24/62
Reference freeze and reference freeze timeout
To prevent an object under detection from influencing the reference value, the ECS is halted
as soon as a proximity detection happens: PTh < Δ(signal) < TTh. Consequently, the
reference is frozen.
In order to recover from a sudden environment change, the reference freeze ends after a
maximum programmable delay called the “reference freeze timeout” (t
When a detection lasts longer than the t
consists of setting the reference to the current burst count value minus 8. Then, ECS is re-
enabled and the reference moves along the signal. After a period of time that depends on
the signal variation speed, the difference between the signal and the reference becomes
smaller than the detection threshold and the device reports no detection. The process delay
after the timeout, to get the reference aligned with the current signal, is called the
recalibration time (t
Figure 14
freeze timeout. The left-hand side of the image (Reference freeze timeout enabled) shows
the reference freeze timeout configured to launch a calibration if water droplets are poured
onto the electrode. The droplet capacitance is not sufficient to make the device enter into
touch detection but it is enough to trigger a proximity detection. If the proximity detection
caused by the droplets lasts longer than the reference freeze timeout delay, the device
recalibrates to the new "wet" environment. Consequently, the detection output is cleared.
The right-hand side of the image (Infinite reference freeze timeout) shows the device
behavior when the reference freeze timeout is disabled. The device leaves proximity
detection only after the droplets are removed.
describes the situation where an unwanted detection is solved by the reference
RECAL
).
Doc ID 18315 Rev 3
RFT
, a recalibration process occurs. The recalibration
RFT
).
STM8T143