A SAW touch screen uses a solid glass display as the touch sensor. Across the surface of the
glass, two surface acoustic sound waves are transmitted – one for vertical detection and the other
for horizontal detection. Each sound wave spreads across the screen by bouncing off reflector
arrays along the edges of the display, and is detected by two receivers for each axis. The time
at which the sound waves arrive at each receiver is known because the velocity of the acoustic
wave through the ...
An infrared touch screen surrounds the face of the display with a bezel of light-emitting diodes
(LEDs) and diametrically opposing phototransistor detectors. A sequence of pulses is directed
to each of these LEDs by the controller circuitry directs, which scan the screen with invisible
infrared light beams just in front of the surface. The controller then detects the location where the
light beams become obstructed by any object.
A capacitive touch screen is constructed out of glass with a coating of capacitive material
electrodeposited over its surface. Oscillator circuits at the corners of the capacitive glass measure
the capacitance of a person touching the glass surface. Each oscillator will vary in frequency
according to where a person touches the surface. The touch screen controller measures the
frequency changes to determine the X and Y coordinates of the touch. The drawback is that
capacitive touch screen cannot be activated by any non-conductive material, including a ...
A resistive touch panel typically uses a conductive glass backplane with a plastic conductive-
coated inner surface. These conductive inner layers are separated by spacer dots evenly
distributed across the active area. Finger or stylus pressure causes internal electrical contact
at the point of touch, which supplies the touch screen controller with a vertical and horizontal
analog voltage for digitization. The three most common formats are:
Digital – Has a discrete number of touch locations determined by a series of rows and columns
of conductors within the ...
The four most common touch screen technologies are: resistive, infrared, capacitive, and SAW
(surface acoustic wave). Resistive and capacitive touch screen technologies are the most popular
for industrial and small format applications. If the application requires that operators wear gloves
when using the touch screen, then resistive is preferred over capacitive. Generally, capacitive
technology offers better optical and touch performance, including multiple touch, but is more
expensive than its resistive counterpart.
Chip-On-Flex is where the LCD driver is mounted directly to a flexible circuited board. These
IC-Flex combinations would come from the driver manufacturer on a reel form referred to as
TAB, or tape automated bonding. In the past, this was a very useful configuration of LCD driver
ICs, as they take up much less space on the LCD glass ledge. However, they are much less
common today due to the additional cost of the film.
Chip-On-Glass is the mounting of the LCD IC directly onto the ledge of the LCD glass itself.
The IC is bonded with an anisotropic conductive film (ACF), which facilitates the mechanical
adhesion, as well as the conduction from the IC to the glass.
Chip-On-Board is the construction method with the LCD driver wafer mounted on the PCB with
contacts facing up. The contacts are then wire bonded to the PCB pads, followed by a complete
epoxy encapsulation for a hermetic seal.
common drivers and segment drivers are the two unique types of driver ICs. common drivers
produce signals to create rows or numbers of lines. Segment drivers produce signals to create the
characters or columns.
The controller IC receives data written in ASCII or JIS code from the MPU. This data in stored
in RAM and is then converted into serial character patterns and transferred to the LCD driver IC.
The most commonly used in monochrome graphic and newer TFT LCD modules, the driver/
controller IC receives data ...
Most LCD controllers can be interfaced by an 8-bit, 4-bit, or 2-bit I2C, or 1-bit interface.