Touch Screen

Factual Questions
1

How does it work?

Don’t ever say 288 in polite company. Its just two gross!

2

Pretty much how you would expect it to work. A screen that fits over your monitor has sensors that detect a voltage change when you touch a particular part of it. The sensors send that information to a prosessor and software driver that translate it into mouse movements.
http://www.touchscreens.com/anatomy.shtml

3

The ones I was familiar with (this was more than a few years ago) used a grid of horizontal and vertical light beams in front of the monitor’s surface. They actually detected where the screen was being “touched” by detecting where an object (such as your finger or a pencil) “broke” those light beams.

Today’s touch-surface screens may well use a different technology.

4

Hey, a question I can answer authoritatively from past experience. I used to work for a defense contractor designing and manufacturing custom displays for rugged applications. Here goes the poop on types of touch screens I have specified and used in the past.

Types of Touch Screens

  1. Resistive - A Resistive touch-screen consists of a glass overlay which has about 4 layers over it. The distance between these layers and thickness of them is in the micro-meter range. When you touch the screen, the controller senses it and computes X-Y coordinates. These displays are suitable for restaurants, hospitals, and manufacturing facilities. They can be sealed against moisture and dirt, and can be operated by a gloved hand. They are durable, but the 4-5 layers make the screen not as bright as other options.

  2. Capacitive - Capacitive touch-screens consist of a glass overlay with a thin metallic conductive coating over the surface of the screen. By touching the overlay surface, a user creates a capacitive coupling with the voltage field, drawing a small amount of current to the point of contact. The amount of current drawn from each corner is used to detect the location of the touch. Typically brighter than resistive screens, capacitive touch-screens are sealed to prevent contamination by water and dirt. They cannot used with a gloved hand. They are subject to drift, thereby requiring calibration now and then and are vulnerable to scratches. Capacitive touch-screens are useful in public information and point-of-sale systems.

  3. Infra-Red - LED Array touch-screens consists of an array of infra-red LEDs (emitters) across the top and one side, and an array of photo transistors (detectors) across the bottom and other side. These set up a mesh of beams, and when a location is touched, some of the X-Y beams are blocked by the finger. There are no overlays so they are very clear and bright. They are subject to false touches, however, especially since the array is often more than a centimeter above the glass. Flies and dust also create problems.

  4. SAW - Surface Acoustic Wave touch-screens consist of a clear glass overlay. Each axis on the overlay has a transmitting and receiving piezoelectric transducer and a set of reflector stripes. The controller sends a 5-MHz burst to the transmitting transducers which convert the signal into surface waves. These are mechanical waves that propagate on the surface of materials such as glass. When the touch-screen it touched, a portion of the wave is absorbed by the finger. This is converted to X-Y coordinates by the controller. These touch-screens are very clear since there is nothing but glass. They are bright, stable, can withstand temp, humidity, etc changes. Scratches do not affect the SAW touch-screens but they do not work well when liquid comes in contact with the screen.

  5. GAW - Guided Acoustic Wave touch screens are very similar to the SAW described above except the vibration pulses actually travel through the glass rather than on the surface. The major advantage of this design is its tolerance for surface contamination. Gloved operation is also possible.

Ursa Major is describing a resistive or capacitive device and WillGolf is describing an Infra-red device. Now if you want to know how to incorporate colored optical filters, linear, circular or elliptical polarizers, anti-reflective or conductive coatings to these touch screens, I get $150.00/hour consulting fees.

5

Uncle Beer: Don’t see yourself short. With the expertise of your response to my short question, your consulting fees should be 300/hr. minimum. I’m going to e mail these responses to my computer “genius” friends who when I asked them the same question, they said “I have no clue”. Thanks to you all!

Don’t ever say 288 in polite company. Its just two gross!