STM8T141 STMicroelectronics, STM8T141 Datasheet - Page 13

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

STM8T141
5.3
5.3.1
Figure 7.
Table 3.
Event description
Detection state
ECF operation
Reference
Environment compensation filter (ECF)
ECF principle
The capacitive sensing channel reference value increases or decreases according to
environmental conditions such as temperature, power supply, moisture, and surrounding
conductive objects. The STM8T141 includes a built-in digital infinite impulse response (IIR)
filter capable of tracking slow changes in the environment called the Environment
Compensation Filter (ECF). This is a first order digital low pass filter with a gain of one. The
filter makes the reference follow slow changes of the signal while fast changes are
recognized as a touch or proximity.
When a touch or proximity condition is detected, the corresponding capacitive sensing
channel reference is frozen.
Environmental compensation filter (ECF) example 1
Explanation of ECF example 1
The object (finger) is
environment is
electrode field
outside the
Electrode
Zone 1
range.
stable
No detection
Adapting
Active
induces a signal change
but, not large enough to
The object, is inside the
electrode field range. It
The reference adapts
slowly to the object
cross the detection
threshold (Dth).
Doc ID 15699 Rev 7
proximity.
Zone 2
The object comes inside the
A touch or proximity event is
reference compensates for
detection range before the
signal level falls below the
triggered because the
reference - D
its presence.
Detection
Zone 3
Frozen
Halt
Th
.
STM8T processing
The object exits
from the
electrode’s
detection range.
No detection
Adapting
Zone 4
Active
13/50