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How Does A Touchscreen Work?

Posted By Tim On July 20, 2012 @ 10:19 AM In I've Always Wanted To Know... | 5 Comments

I’ve Always Wanted To Know:
How does a touchscreen work?


Answer:

Touchscreens let us interact with computers, tablets, phones, remote controls and a host of other things with great ease but how do they work?

There are two types of touchscreens used in many devices and they work very differently.

Resistive:

(Image courtesy of PlanarTouch [1])

Resistive touch screens were commonly used before Apple introduced the iPhone in all touchscreen devices work by having two layers of conductive material separated by air gaps. When you apply pressure to an area of the screen a circuit completes and the device is given a coordinate where the circuit was completed. Think of it like putting a dot on a piece of graph paper. The screen reports that the dot is at the 7th box up 3 boxes in from the left. You can usually identify these screens by the flexible plastic like outer layer.

Positives of Resistive Touchscreens:

  • Cheap to produce.
  • Can be used with gloves, stylus or pointing devices.

Negatives to Resistive Touchscreens:

  • Can only detect one point  of contact (one finger) at a time on most touchscreens.
  • Not as resilient/durable as other touchscreens as layers must be made of flexible material.
  • “Feel” of touch screen not as smooth/responsive as other technologies.

Capacitive:

(Image courtesy of PlanarTouch [1])

Capacitive touchscreens first introduced to the market with the Apple iPhone work by applying a very light current to all 4 corners of the screen. When a finger or other specially designed stylus touch the screen there is a circuit created and a voltage drop develops and sensors register the location of the voltage drop. You can usually identify these screens by a hard glass outer layer.

Positives of Capacitive Touchscreens:

  • Very responsive to touch with natural movements.
  • Able to detect multiple points of contact (fingers) to enable pinch zooming, swiping and other hand motions.
  • Hard outer glass layer makes for very high quality displays with vibrant colors and high contrast ratios.

Negatives of Capacitive Touchscreens:

  • Touch input does not work if your wearing gloves (special touch enabled gloves are availible)
  • Screens often very reflective reducing outdoor useability.
  • Much more expensive to produce.

So which touchscreen technology do you want? That depends on the application. If I was choosing a touchscreen technology for my next tablet or computer I would want a capacitive display. If I wanted a touchscreen for a control panel on an industrial lift I might choose resistive so it could be operated with work gloves on.

-Tim


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URLs in this post:

[1] PlanarTouch: http://www.planartouch.com/