STM8T141 STMicroelectronics, STM8T141 Datasheet - Page 10

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

STM8T ProxSense technology
4
4.1
4.2
10/50
STM8T ProxSense technology
Capacitive sensing overview
A capacitance exists between any reference point and ground as long as they are
electrically isolated. If this reference point is a sensing electrode, it can help to think of it as
a capacitor. The positive electrode of the capacitor is the sensing electrode, and the
negative electrode is formed by the surrounding area (virtual ground reference in
Figure 4.
When a conductive object is brought into proximity of the sensing electrode, coupling
appears between them, and the capacitance of the sensing electrode relative to ground
increases. For example, a human hand raises the capacitance of the sensing electrode as it
approaches it. Touching the dielectric panel that protects the electrode increases its
capacitance significantly.
Charge transfer acquisition principle
To measure changes in the electrode capacitance, STM8T devices employ bursts of charge-
transfer cycles.
The measuring circuitry is connected to the C
plus the sensing electrode itself of equivalent capacitance C
electrode can be made of any electrically conductive material, such as copper on PCBs, or
transparent conductive material like Indium Tin Oxide (ITO) deposited on glass or Plexiglas.
The dielectric panel usually provides a high degree of isolation to prevent ESD discharge
from reaching the STM8T touch sensing controller. Connecting the serial resistor (R
C
X
pin improves ESD immunity even more.
Coupling with hand increases the capacitance of the sensing electrode
Lower capacitance
C
X
Doc ID 15699 Rev 7
Sensing electrode
X
pin. It is composed of a serial resistor R
Higher capacitance
X
(see
C
Figure
T
5). The sensing
STM8T141
Figure
X
) to the
X
4).