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touch sensor basics

This page covers touch sensor basics and mention touch sensor types.

Now-a-days all the modern electronic devices are touch based. These have been used in ATMs, information kiosks, smart mobile devices, vending machines etc. These touch screen devices are developed based on touch sensors. These provides easy user navigation based on easy GUI functionalities incorporated.

touch Sensor types

There are various touch sensor types such as 5-wire(or 4-wire) resistive, surface capacitive, projected capacitive, surface acoustic wave and Infrared sensors.

Wire resistive Sensor : In this type of sensor, when user touches screen, two metallic layers make contact. This results into flow of current. The point of contact is determined based on change in the voltage. This type of touch sensors are more affordable but they are damaged with the use of sharp objects.

Surface capacitive Sensor: This sensors are activated with the touch of human skin or a stylus holding an electrical charge. In this type of monitor, a transparent electrode film is placed on top of the glass panel. When exposed finger touches the monitor screen, it reacts to the static electrical capacity of the human body. Some of the charge will get transfer from the screen to the user. The change in capacitance(decreased) is detected by sensors located at the four corners of the screen. This allows the controller to determine the touch point.

Projected capacitive Sensor: This type of touch sensor is similar to surface capacitive type. It offers two merits compare to surface capacitive. It can also be activated with the application of surgical gloves as well as thin cotton gloves. It also detects multiple touch points.

This type of sensor has sheet of glass with embedded transparent electrode films and an IC chip. This create 3 dimentional electrostatic field. When a finger comes in direct contact with the screen, ratios of electrical current will change and hence system will detect touch points.

Surface Acoustic Wave Sensor: SAW touchscreen monitors utilize a series of piezoelectric transducers and receivers. This creates grid of ultrasonic waves on the surface. The other element is placed on the glass referred as reflector. When a panel is touched, portion of the wave is absorbed. This will help receiving transducer to locate the touch point and send this data to the system.

Infrared Sensor: This type of touch screen sensor is based on interruption of light path in an invisible light grid in front of the screen. If an obstable appears inside the grid matrix. it will interrupt the light beams and will cause reduction in measured photo current in the detectors. Based on these informations, X-Y co-ordinates can be determined.

In this type of infrared sensor, array of emitters are placed behind two adjacent bezels of the screen frame. This creates the optical grid as mentioned above.

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