4.1 Capacitive Detection Method

The capacitive method for liquid detection relies on the principle that the presence of a liquid changes the dielectric constant of the medium between two conductive plates, which in turn affects the system capacitance. The capacitance of the sensor electrode attached to the S_CAP pin is measured periodically. The period can be provided through the SLP_PER pin or through the Enhanced Configuration. The increased dielectric constant results in a higher capacitance value when the liquid is present. Conversely, when the liquid is absent, the capacitance value is lower.

The capacitive sensor input pin is connected to the sensor electrode via a series resistor to reduce the Electromagnetic Interference (EMI) and increase Electromagnetic Compatibility (EMC). The series resistor can be from 1 kΩ to 100 kΩ, depending on the sensor capacitance and desired level of EMC performance. For further details, refer to Microchip Application Note (AN2934) - Capacitive Touch Sensor Design.