Touch Screen   
 

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The most intuitive interface in the computer industry today is the touch screen. By placing a touch screen over an LCD a computer system can be controlled by the user simply touching the display. Touch screen technology has improved over the years allowing producers to offer this state of the art solution at a low cost. The touch screen kit consists of a resistive touch screen that uses a thin flexible membrane separated from a glass substrate by insulating spacers. The substrate surface and the facing membrane have transparent mechanical coatings that contact when a finger or stylus presses on the screen. This effectively produces two resistive values which are read by the Touch controller. The on board microprocessor converts this analog value to x and y coordinates and transmits them to the computer’s RS-232 serial port. The touchscreen glass can be attached to the front of the LCD or its enclosures bezel. The controller plugs directly into a nine pin DB-9 serial port. Touch drivers are easy to install and use. Mouse emulation drivers for DOS and Windows are included. Sample ‘C’ source code is available for embedded applications.

Touch Kits include 1) Touch screen, 2) Touch RS-232 touch controller, 3) a power supply and 4) Touch Drivers for Windows & Windows 95.

FAQ:

Q. How do I interface my program to the touchscreen?

A. While there is a programming API available, the easiest is just to use the touch screen's mouse emulation, if your program uses a mouse, it already works with touch!

Q. How do I attach the touchscreen to the LCD?

A. You can use thin double sided tape to attach the touch glass to the frame of the LCD or to your enclosure's bezel and mount the LCD flush from the rear of your enclosure.

Q. How does the touchscreen controller work?

A. It takes x & y values from where the user touches the touchscreen and converts them to mouse coordinates transmitting them to your P.C.'s RS-232 port.

Q. Can I write my own touch software?

A. Yes you can, click here to download the 124 page PDF .

Q. What is resistive touch technology?

A. Resistive touch technology consists of a glass or like panel that is coated with electrically conductive and resistive layers. The thin layers are separated by invisible separator dots. While turned on, an electrical current moves through the screen casting a sort of net across the monitor face. When you touch the screen (creating pressure) the layers are pressed together, causing a change in the electrical current and a touch command to be registered.

Reliability is impressive because resistive touch screens do not have to be recalibrated when environmental conditions change. Resistive-type touch screens are usually the most practical. Resistive screens are extremely durable and can withstand the harshest of environments. Resistive technology is the “work horse” of touch technologies.

This type of screen is recommended for point of sale systems-kiosks (POS), restaurant registers, control or automation systems,
medical use, hospitality kiosks, grocery/convenience, standard kiosks and others.

Q. What is capacitive touch technology?

A. A Capacitive Touch screen consists of a glass panel with a capacitive (charge storing) material coating its surface. Circuits located at corners of the screen measure the capacitance of a person touching the overlay. Frequency changes are measured to determine the X and Y coordinates of the touch command.

Capacitive type touch screens are very durable and have high clarity. They are used in a wide range of applications, from restaurant and point of sale (POS) use, to industrial controls and information kiosks.

Side by side touch screen technology comparison:

Technology

Capacitive

Resistive

Surface Acoustic Wave (SAW)

Optics/Clarity

85% light transmission, excellent clarity

75%, Clear finish, good clarity

90% light transmission, excellent clarity

Durability

Excellent, contains hardened glass surface with conductive under coating

Good, contains hardcoated plastic overlay, subject to vandalism

Excellent, contains no overlays, all glass panel

Reliability

Very High

High

Very High

Accuracy, Calibration Stability

Very accurate, very stable

Very Accurate, very stable

Extremely Consistent, Very Stable,

Activation, Sensitivity

Finger contact for touch activation. Easily detects contact.

Pressure sensitive. Activated by any object, good for gloved applications.

Soft objects, Non-glare requires significant contact.

Touch Resolution

Very High (> 250pts./in.) 4096 x4096

High (>200 pts./in.)

Very high (>200 pts./in.) 4096 x4096

Response Time

8-12 milliseconds

5-10 milliseconds

10-15 milliseconds

Stylus

Conductive Only

Hard or Soft, not sharp

Soft Only

Sealing

Easy

Must seal in inactive area

Must seal in active area with low acoustic absorption materials

Parallax

Low

Low

Low

Z-Axis

None

None

Yes-255 levels of pressure

Multiple Touch

Averages simultaneous touches

Averages simultaneous touches

Rejects simultaneous touches

Touch Life

Many Millions of touches

Millions of touch

Many Millions of touches

Controllers Available

RS-232 Serial, PS2, USB, PC-Bus, or Mac ADB

RS-232 Serial, PS2, USB, PC-Bus, or Mac ADB

RS-232 Serial, PC-Bus, or Mac ADB

Sealing from environment

Very easy

Very easy

Difficult

Main Problems

Must make contact with conducting object(finger/stylus)

Scratches easiest

Moisture, dirt and dust creating dead zones

Maintenance Required

Normal cleaning of finger prints

Normal cleaning of finger prints

Requires most cleaning in dusty environments

 

Manufacturers:

Advantech

EarthLCD

EloTouch

MicroTouch (3M)

ICP-Electronics

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Copyright © 2002 Øyvind Haugland
Sist endret:  13 januar 2019
 

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