How Do Touchscreens Work?

A complete overview of the most modern touch screen technologies


 
Have you ever wondered how touchscreens work? A few years ago touchscreens were futuristic and only used in industrial applications. Today we don't even think twice before tapping or swiping a touchscreen around us. Even toddlers know how to work them and play their favourite Dora or Teletubbie video.

ATM machines, smart phones and kiosks are hardly ever seen without a touchscreen anymore. The biggest advantage for users is the interactivity a touchscreen offers. It's easier for people to interact with a device using their finger than it is to point a mouse to the right location. But did you know there are several unique touchscreen technologies? Find out how touchscreens work and what different technologies there are.

 

 


 

Need some help with all the touch screen terminology?  

>> Download our Free Touch Screen Glossary for industry touch terms <<

 


 

 

How a Touchscreen Works and Why They Crave (Skin) Contact

 

First of all, it's good to know there is not one way a touchscreen works. Each technology operates differently. This means the touchscreen in your local ATM and the one in your iPhone are completely different. All touch technologies mentioned below can still be purchased. However, resistive and projected capacitive touchscreens are used most in todays' applications.

 

 

 

Resistive Touch Screens

How Resistive Touch Works
Screens you tap at the ATM, supermarket check outs or kiosks are usually fitted with a resistive touchscreen. The resistive touch technology is the most widely used touch technology today. A resistive touchscreen consists of two thin flexible metallic layers with a gap in between. These two layers have an electric current running through them. When touched the top flexible layer touches the bottom one, interrupting the electrical current. The device notices this and detects the point of contact by the change in electrical flow. Of course this all happens at warp speed.

Resistive touch is one of the cheapest touch technologies out there. A resistive touchscreen responds to pressure and doesn't care what object applies the pressure. A finger, glove or stylus will all work. Swiping and multi touch do not work, because this technology only registers one touch point. That is why a resistive touchscreen doesn't work on smartphones or tablets (what would we do without swiping?). The actual display is always situated behind the touch layers. But these layers are not quite as clear as glass. That is why ATM's and in-flight entertainment screens are a bit hazy.

Advantages

  • Use pretty much any object to touch - finger, stylus, pen, gloved hand, etc.
  • Solid feel
  • Lowest cost
  • Low power consumption
  • Resistant to surface contaminants and liquids - dust, oil, grease, water, etc.


Disadvantages

  • Image clarity not as great as other technologies
  • Outer touch layer is vulnerable to damage - scratching, poking with sharp objects, etc.

 

What is the difference between resistive and capacitive touch? +


 

 

Capacitive Touch Screens

How Capacitive Touch Works
For a long time capacitive touch was the second most popular touch technology out there. A capacitive touchscreen uses a transparent electrode layer. This layer is placed on top of a glass panel and covered by a protective layer. When a finger touches the touchscreen, some of the electrical charge transfers from the screen to the user. Sensors in all four corners of the screen detect the decrease of electric current. The controller than determines the touch point. Capacitive touchscreens can only be activated when touched by human skin or a stylus holding an electrical charge. Despite its long term popularity, capacitive touch now gets replaced by projected capacitive touchscreens.

Advantages

  • Great image clarity (better than resistive touch)
  • Durable screen
  • Excellent resistance to surface contaminants and liquids - dust, grease and water
  • High scratch resistance


Disadvantages

  • Only works with bare finger or special capacitive stylus
  • Sensitive to EMI (Electromagnetic Interference) and RFI (Radio Frequency Interference)


 

 

Projected Capacitive Touch Screens (PCAP)

How PCAP Touch Works
A Projected capacitive touchscreen works very similar to regular capacitive touchscreens. They do offer two great advantages. Next to a bare finger, they also work with surgical gloves or thin cotton gloves. And they make multi touch possible. Multi touch means when two fingers simultaneously activate the touchscreen. A projected capacitive touchscreen consists of a sheet of glass with embedded transparent electrode films and an IC chip. This creates a three dimensional electrostatic field. A change in the electrical currents is noticed when a finger touches the screen. A touch point is then detected. Projected capacitive touchscreens are being used more and more. They are generally chosen over regular capacitive touchscreens because of their durability.

Advantages

  • Excellent image clarity
  • More resistant to scratching than capacitive touch
  • Resistant to surface contaminants and liquids
  • Multi touch possible


Disadvantages

  • Sensitive to EMI (Electromagnetic Interference) and RFI (Radio Frequency Interference)
  • Only activates using an exposed finger, thin surgical gloves or cotton gloves

 

Looking for even more information on Projected Capacitive Touch Screens? +


 

 

Infra Red Touch Screens

How Infra Red Touch Works
Unlike other technologies, infra red touchscreens don't overlay the screen with an extra layer. These types of touchscreens are based on light beam interruption technology. An infra red touchscreen uses infra red emitters and receivers. They create an invisible grid of infra red light beams across the screen. No extra film or layer means the best possible image quality and clarity. A sensor detects the touch when an object interrupts the light beams.

Advantages

  • Best image quality of all touch technologies
  • Unlimited 'touch life'
  • Unaffected to surface scratches


Disadvantages

  • Accidental touches may occur when the light beams are accidentally above the glass surface.
  • Grease, dust or other contaminants could block light beam
  • Sensitive to water, snow and rain
  • May be sensitive to ambient light
  • More expensive


 

 

Optical Touch Screens

How Optical Touch Works
Optical touchscreens use multiple optical sensors to detect the touch. The sensors actually detect the touch just before the user makes physical contact with the screen. This means you don't even have to completely touch the screen or can touch it very lightly. Because optical touchscreens don't use electrical currents, they can be activated using any object. A finger, gloved finger, stylus or pen are all great input devices for an optical touchscreen.

Advantages

  • Enables multi touch
  • No pressure needed to register a touch
  • 100% light transmission
  • Scratches do not affect the touchscreen 
  • Use any object to touch


Disadvantages

  • Direct sunlight can affect the touchscreen
  • Depth of monitor increases by frame

 

 

Surface Acoustic Wave (SAW) Touch

How SAW Touch Works
A Surface Acoustic Wave (SAW) touchscreen works a little different than resistive and capacitive touchscreens. SAW touchscreens use transducers mounted to the edge of a glass panel. The transducers create an invisible grid of ultrasonic waves on the surface which are received by sensors. Hence the name surface acoustic wave. When a user touches the screen, some of this wave gets absorbed. The receivers locate the touch point and send this information to the computer. SAW touchscreens can be activated using a finger, gloved hand or stylus. They are easy to use and offer high visibility.

Advantages

  • Good optical clarity
  • Even better scratch resistance than capacitive touch
  • High 'touch life'


Disadvantages

  • Cannot be activated with hard objects - pens, credit cards or fingernails
  • False touches are an option - like by water droplets
  • Solid contaminants on the screen can create non-touch areas until removal

 

 

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