Capacitance change is measured through the dielectric difference caused by a finger touch.
The increasing in the dielectric constant cause the voltage to drop initially. Therefore, a current can be measured through the sensing resistor and the op-amp.
The opAmp output then connects to a Schmitt trigger(implemented by an opamp) to be filtered.
Through a Cmos inverter, the signal ends up in the clock of the D latche based flip flop to satisfy the talking behavior.
