In present scenario, touch sensors are also known as tactile sensors. The basic working principle of a touch sensor is that it detects near proximity (also known as touch) without depending on physical contact. In simple words, you can understand that its working is same as a simple switch or circuit. When any physical medium comes in contact with the touch surface. The internal circuit will be closed inside the sensor and current starts flowing. On the other hand, when this physical contact is broken or released, the circuit will opened.
Below circuit illustrates that how the resistive touch sensor works.
The above circuit shows the basic working of the touch sensor which consist of the touch electrode or the surface.
The resistive touch sensor operates when an object with some resistivity such as our finger touches the surface. Touch of the object with a little resistance forms a close circuit which allows an small amount of current to flow.
In the above circuit the touch causes a very little current to flow.
The transistor amplifies the voltage to some significant value.
Resistance Rp is used to protect the transistor from the high current.
It is useful In case if there is a fault occurs in the electrodes.
Resistance Rb is used to keep the base of the transistor grounded.
There is no current when there is an open circuit or if there is no pressure applied.
When the little pressure is applied on the electrode. There is an small flow of current through the base of the transistor. The current enables the resistive touch sensor and the current flows through the load.