Arduino capacitive touch sensor
In capacitve sensing when we bring human body near to the sensor a capacitance is build between the sensor and human body. Human body(suppose the tip of finger) and sensor body behaves like the plates of the capacitor and a charge is induced between the plates. This charge is picked by the sensor and is translated as a button press. As we move our finger back from the sensor plate the capacitance is lost and circuit breaks.
The most popular arduino capacitve touch sensor available in the market is one based on TTP223 touch sensor ic. The equivalent circuit of the touch module is given in the below diagram. In the circuit of the TTP223 below if we bring our finger tip near to the touch pad our finger and touch pad builds a capacitor. This new capacitor is in parallel to capacitor C1. Recall capacitor in parallel increases capacitance. So the capacitance increases and a charged is induced in the capacitor. This induction is picked by the sensor as a button press.
Note: We don’t need to touch our finger tip to touch plate. Capacitor can be build by taking our finger near the touch plate. Since the distance needed to build capacitor is in nano meters so usually we touch our finger to the touch plate.
Arduino Metallic touch sensor
Capacitive touch sensor with arduino uno
Circuit diagram of the project is given below. Touch sensor signal pin is connected to arduino digital pin 2. Buzzer cathode is connected to digital pin 9 of arduino uno. Both the buzzer and capacitive touch sensor is powered through the 5 volt output of arduino regulator.