A touch switch is a type of

switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...

that only has to be touched by an object to operate. It is used in many

lamp Lamp, Lamps or LAMP may refer to: Lighting * Oil lamp, using an oil-based fuel source * Kerosene lamp, using kerosene as a fuel * Electric lamp, or light bulb, a replaceable component that produces light from electricity * Light fixture, or ligh ...

s and wall switches that have a metal exterior as well as on public computer terminals. A

touchscreen A touchscreen or touch screen is the assembly of both an input ('touch panel') and output ('display') device. The touch panel is normally layered on the top of an electronic visual display of an information processing system. The display is often ...

includes an array of touch switches on a display. A touch switch is the simplest kind of

tactile sensor A tactile sensor is a device that measures information arising from physical interaction with its environment. Tactile sensors are generally modeled after the biological sense of cutaneous receptor, cutaneous touch which is capable of detecti ...

Types

There are three types of switches called touch switches:

Capacitance switch

A capacitance switch needs only one electrode to function. The electrode can be placed behind a non-conductive panel such as wood, glass, or plastic. The switch works using

body capacitance Body capacitance is the physical property of the human body that has it act as a capacitor. Like any other electrically-conductive object, a human body can store electric charge if insulated. The actual amount of capacitance varies with the surrou ...

, a property of the human body that gives it great electrical characteristics. The switch keeps charging and discharging its metal exterior to detect changes in

capacitance Capacitance is the capability of a material object or device to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized are ...

. When a person touches it, their body increases the capacitance and triggers the switch. Capacitance switches are available commercially as

integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...

s from a number of manufacturers. These devices can also be used as a short-range

proximity sensor A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact. A proximity sensor often emits an electromagnetic field or a beam of electromagnetic radiation (infrared, for instance), and looks for ...

Resistance touch switch

A resistance switch needs 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. It is thus much simpler in construction compared to the capacitance switch. Placing one or two fingers across the plates achieves a turn on or closed state. Removing the finger(s) from the metal pieces turns the device off. One implementation of a resistance touch switch would be two Darlington-paired transistors where the base of the first transistor is connected to one of the electrodes. Also, an N-channel, enhancement-mode, 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.

Piezo touch switch

Piezo touch switches are based on mechanical bending of piezo ceramic, typically constructed directly behind a surface. This solution enables touch interfaces with any kind of material. Another characteristic of piezo is that it can function as

actuator An actuator is a component of a machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover". An actuator requires a control device (controlled by control signal) a ...

as well. Current commercial solutions construct the piezo in such a way that touching it with approximately 1.5 N is enough, even for stiff materials like stainless steel. Piezo touch switches are available commercially.

Comparison

Piezo switches respond to a mechanical

force In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a p ...

applied to the switch. The switch will operate regardless of whether force is applied through insulating or conducting materials. Capacitive switches respond to an

electric field An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...

applied to the switch. The field will pass through thin gloves, but not through thick gloves. Piezo switches usually cost more than capacitive switches.

Lamps

References

External links

HowStuffWorks.com answer to question: How do touch-sensitive lamps work?

Example schematics

Touch with more intelligenceCapacitance touch switchResistance touch switch
{{Switches Switches