Satya Sravan
2nd year
Electronics & Communication Engg.
Hope many of us use a touchscreen mobile or a gadget with touch screen interface. Did you ever think what the technology behind touchscreen is? Let’s know what a touchscreen is, how it works and about the technology behind its operation.
A touchscreen is an electronic visual display that can detect the presence and location of a touch within the display area.The touch screen is one of the easiest to use and most intuitive of all computer interfaces. The touchscreen interface is being used in a wide variety of applications to improve human-computer interaction.
HOW IT WORKS ?
Basically, there are three components used in touch screen technology.
- Touch sensor, a panel with a touch responsive surface.
- Controller, the hardware that converts the voltage changes on the sensor into signals the computer or other device can receive.
- Software, tells the electronic devices what's happening on the sensor and the information coming from the controller.
TOUCH SENSORS
Systems are built based on different types of sensors: resistive (most common), surface acoustic wave, and capacitive (most smart phones).
RESISTIVE TOUCHSCREEN TECHNOLOGY
The resistive system is comprised of five components, including the CRT (cathode ray tube) or screen base, the glass panel, the resistive coating, a separator dot, a conductive cover sheet and a durable top coating.
The two metallic layers become connected when a finger or stylus presses down on the top surface. The surface acts as a pair of voltage dividers with connected outputs. This causes a change in the electrical current. The pressure from your finger causes conductive and resistive layers of circuitry to touch each other, changing the circuits' resistance, which registers as a touch screen event that is sent to the computer controller for processing.
HOW IT LOOKS
WORKING
OPERATION
CAPACITIVE TOUCHSCREEN TECHNOLOGY
The touch pad contains a two-layer grid of electrodes that are connected to a sophisticated full-custom mixed signal integrated circuit (IC) mounted on the reverse side of the pad. The upper layer contains vertical electrode strips while the lower layer is composed of horizontal electrode strips.
A human finger near the intersection of two electrodes modifies the mutual capacitance between them, since a finger has very different dielectric properties than air. When a user touches the screen, some of the charge is transferred to the user, and makes the potential difference on the screen. After the panel controller recognizes that, the controller will send the X-Y axis information to the PC port.
Capacitive technology includes technology based on the surface capacitance, projected capacitance, mutual and self-capacitance.
The advantage is that capacitive technology transmits almost 90% percent of the light from the screen.
HOW IT LOOKS
WORKING
WORKING
OPERATION
SURFACE ACOUSTIC WAVE (SAW) TECHNOLOGY
It is one of the most advanced touch screen types.The technology is based on two transducers (transmitting and receiving) placed for the both of X and Y axis on the touch panel. The other important element of SAW is placed on the glass, called reflector.
The controller sends electrical signal to the transmitting transducer, and transducer converts the signal into ultrasonic waves and emits to reflectors that are lined up along the edge of the panel. After reflectors refract waves to the receiving transducers, the receiving transducer converts the waves into an electrical signal and sends back to the controller. When a finger touches the screen, the waves are absorbed, causing a touch event to be detected at that point.
WORKING
OPERATION
INFRARED TOUCHSCREEN TECHNOLOGY
The Infrared Touch Screen is a frame which is integrated with a printed circuit board that contains a line of IR-LEDs and photo transistors hidden behind the bezel of the touch frame. Each IR-LEDs and phone transistors are hidden behind the invisible infrared light. The bezel covers the parts from the operation environment while allowing the IR beams to pass through.
The controller sequentially pulses LEDs to create a grid of IR light beams. When a user touches, the screen enters the grid by a stylus which can interrupt the IR light beams. The photo transistors from X and Y axes coordinates to the host.
Other technologies include optical imaging, dispersive signal technology, strain-gauge touch screen technology and acoustic pulse recognition.
COMPARISON TABLE
RESISTIVE | CAPACITIVE | SAW | INFRARED | |
Accuracy | 2% of screen dimension | 1% of screen dimension | 1% of screen dimension | 1% of screen dimension |
Resolution | 16K x 16K | 10K x 10K (approx.) | 384x16 | |
Light transmission | <= 82% overall | <= 88% @ 550nm | <= 92% overall | 92%, Up to 100% |
Operating temperature | -20C to +50C | -15C to +70C | -20C to +50C | -20C to +85C |
Operation | Finger or stylus | Finger only | Finger or soft-tipped stylus | Finger or stylus |
Positive talk | More accurate and durable, low cost | Repeatability, no moving parts, protective overcoat | Good response, reliability, easy to maintain | High resolution, clarity, durability, safety. |
Negative talk | Optics are not much better, easily vandalized | Less transmission, expensive, affected by EMIR | Hard to integrate, affected by humidity & dirt | Highly sensitive |
CONCLUSION
The touchscreen technology is used in ATMs, Self-Checkout Counters, Airport Check-in, PDAs, Tablet PCs, Mobile Phones, Handheld Gaming Consoles, Multi-Touch Collaboration Wall, image processing and image capture etc.
Touch screen technology will increase in significance as an I/O technique for user oriented embedded systems. The steady improvement in the use of touch sensors punctuated by innovation will continue to broaden the range of applications that touch screens can serve.
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