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Touch Monitors
Touch Computers
Point of Sales
Kiosks
Touch Overlays
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Resistive
The sensor consists of a piece of
glass with a conductive coating on top, plus a polyester top sheet with a
conductive coating on the bottom. The conductive surfaces are held apart by
“spacer dots”, usually glass beads that are silk-screened onto the coated
glass. On a 5-wire design (the most commonly used type of resistive in large
screen POS applications); a voltage is applied to the 4 corners of the glass
layer. When a person presses on the top sheet, it is deformed and its
conductive side comes in contact with the conductive side of the glass,
effectively closing a circuit. The voltage at the point of contact is read
from a wire connected to the top sheet.
Advantages
Can be activated with any device
Low cost solution
Low power consumption
Disadvantages
Poorer durability compared to other technologies
Poorer transmittance and overall optical quality
Requires periodic recalibration
Surface Acoustic Wave (SAW)
A SAW touch screen consists of a piece of glass with “sound wave reflectors”
deposited along all 4 edges. Two emitting transducers are mounted in two
corners and receivers are mounted in the opposing two corners. A sound wave
travels parallel to the borders of the glass. As it encounters the sound
wave reflectors, some of it is passed through to the next sound wave
reflector, and some of it is reflected across the touch screen. On the
opposite side, the wave is passed through the sound wave reflectors to the
receivers. The receivers can detect a drop in amplitude of the sound wave
when a sound absorbing material (such as a finger) is placed in contact with
the glass.
Advantages
Very high transmittance
Very high durability
Disadvantages
Cannot be sealed
Requires “soft” input device
Surface obstructions can cause a false touch
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Capacitive
The capacitive sensor has a conductive coating on the front surface with
wires connected to each corner. A small voltage is applied to each of these
4 corners. The operation relies on the capacitance of the human body. When a
person touches the screen, a small current flows to the point of touch,
causing a voltage drop which is sensed at the 4 corners.
Advantages
More durable than resistive (because the top layer is not
plastic)
Higher transmittance than resistive (fewer layers)
Disadvantages
Accepts input from finger only (or a special, tethered
conductive stylus)
Susceptible to electromagnetic interference can cause an
erratic cursor location
Accuracy is dependent on capacitance of person touching the
display
Requires periodic calibration
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Scanning Infra Red (IR)
IR uses of a Printed Circuit Board (PCB) “frame” around the perimeter of the
display. On two sides there are closely spaced IR LEDs and on the opposing
two sides there are matching photo transistors. The LEDs are turned on in
sequence and the signal is read from the matching transistor. If no signal
is read, then that indicates a blocked IR beam, meaning a touch. No actual
touch “screen” is required for operation, however a plate of glass is
generally used to protect the underlying display from damage and to provide
anti-glare.
Advantages
Highest quality of underlying image
Very high transmittance (no conductive layers, only glass
between image)
Excellent anti-glare, with use of chemically etched glass
Can be activated with almost any device
Higher accuracy than other technologies
Very high durability and reliability
One time factory calibration
Can be sealed
No wear mechanism
Disadvantages
Lower resolution than other technologies
Surface obstructions can cause a false touch
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