A touch switch is a type of switch that only has to be touched by an object to operate. It is used in many lamps and wall switches that have a metal exterior as well as in public computer terminals. A touch screen includes a series of touch switches on one screen. A touch switch is the simplest type of touch sensor.
Types
There are three types of switches called touch switches:
Capacitance Switch
A capacitance switch only needs one electrode to operate. The electrode can be placed behind a non-conductive panel, such as wood, glass or plastic. The switch works using the capacitance of the body, a property of the human body that gives it great electrical characteristics. The lamp continues charging and discharging its metal exterior to detect changes in the capacitance. When a person touches it, it increases the capacitance and triggers the switch. Capacitance switches are commercially available as integrated circuits from various manufacturers. These devices can also be used as a short-range proximity sensor.
Touch resistance switch
A resistance switch requires two electrodes to be physically in contact with something electrically conductive (for example a finger) to operate. They work by lowering the resistance between two pieces of metal. Therefore, it is much simpler in construction compared to the capacitance switch. Placing one or two fingers through the plates achieves a power-on or closed state. Removing the finger (s) from the metal parts disables the device. One implementation of a resistance touch switch would be two Darlington-paired transistors in which the base of the first transistor is connected to one of the electrodes. Also, an N-channel, mode-enhancing metal oxide field-effect transistor can be used. Its gate can be connected to one of the electrodes and the other electrode through a resistance to a positive voltage.
Piezoelectric Touch Switch
The piezoelectric touch switches are based on mechanical piezo-mechanical folding, typically built directly behind a surface. This solution allows tactile interfaces with any type of material. Another piezo feature is that it can function as an actuator as well. Current commercial solutions build the piezo in such a way that playing with approximately 1.5 N is sufficient even for rigid materials such as stainless steel. Piezo touch switches are commercially available.