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 on public computer terminals. A touchscreen
A touchscreen is an electronic visual display that can detect the presence and location of a touch within the display area. The term generally refers to touching the display of the device with a finger or hand. Touchscreens can also sense other passive objects, such as a stylus...
includes an array of touch switches on a display.
A touch switch is the simplest kind of tactile sensor
The term tactile sensor usually refers to a transducer that is sensitive to touch, force, or pressure. Tactile sensors are employed wherever interactions between a contact surface and the environment are to be measured and registered...
Capacitance touch 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 a biological property of the human body that makes it a good capacitor and able to store charge. Every person has a characteristic called capacitance. Capacitance is an electronics term that has units of measure called farads. Capacitors are electronic components that store...
, a property of the human body that gives it great electrical characteristics. The lamp keeps charging and discharging its metal exterior to detect changes in capacitance
In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...
. When a person touches it, it increases the capacitance and triggers the switch.
Capacitance switches are available commercially as integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
- Analog Devices
Analog Devices, Inc. , known as ADI, is an American multinational semiconductor company specializing in data conversion and signal conditioning technology, headquartered in Norwood, Massachusetts...
: Model AD7147 (12 channel).
Microchip can also refer to:* Integrated circuit, a set of electronic components on a single unit.* Microchip Technology, a company that makes popular 8, 16 and 32-bit microcontroller lines.* Microchip implant , a microchip implanted into animals....
mTouch: Model PIC16F707 (32 channel).
- Cypress Semiconductor
Cypress Semiconductor Corporation is a Silicon Valley-based semiconductor design and manufacturing company founded by T. J. Rodgers and others from Advanced Micro Devices. It was formed in 1982 with backing by Sevin Rosen and went public in 1986. The company initially focused on the design and...
CapSense: The CY8C21434 can be configured as an 8-channel capacitance sensor, as used in the Apple iPod
Atmel Corporation is a manufacturer of semiconductors, founded in 1984. Its focus is on system-level solutions built around flash microcontrollers...
QTouch: QTouch series of semiconductors including the simple QT 1010/1/2 devices.
is a Japanese electronics company based in Kyoto.Omron was established by Kazuma Tateishi in 1933 and incorporated in 1948. Omron's primary business is the manufacture and sale of automation components, equipment and systems, but it is generally known for medical equipment such as digital...
: Model B6TS04LT (4 channel) and B6TS08LT (8 channel).
- Freescale Semiconductor
Freescale Semiconductor, Inc. is a producer and designer of embedded hardware, with 17 billion semiconductor chips in use around the world. The company focuses on the automotive, consumer, industrial and networking markets with its product portfolio including microprocessors, microcontrollers,...
: Model MPR083 and MPR084 can be configured as an 8-touch-pad sensor.
- touchSEMI: Model TSM12 (12 channel) and complete touch sensors and capacitance comparators line.
- Rapid Keypads: Model BSQ-XX2ML (6 - 32 channel) ICs communicate via USB, Serial, SPI, I2C and other custom communication protocols.
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 or a beam of electromagnetic radiation , and looks for changes in the field or return signal. The object being sensed is often referred to as...
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
In electronics, the Darlington transistor is a compound structure consisting of two bipolar transistors connected in such a way that the current amplified by the first transistor is amplified further by the second one...
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.