Smartphone Screens – Confused??


Since 2009, mobile phone industry has emerged itself into the smart-phone technology. Now smart-phones are giving a tough competition to the tabular PC generation.

So even if you’re don’t own a smart-phone and planning to buy one, I’m pretty much sure that you will wind up with a touchscreen one. Rather all smart-phones have one. Each time a new phone is launched you get to see lots and lots of new features. In short touch screens have now become a trend & will continue to be.

With this advent, touch screen technology has under gone massive technological enhancements. At present buyers are quite confused on which technology to go for.

In general there are two main touchscreen technologies available for smart-phones.

1. Resistive Touch screens.

2. Capacitive Touch screens.

Before you start boasting your new phone’s touch screen technology, you must first know what they actually mean and why and when to go for each touch screen technology type. Of course not all of us would need to know the technicalities behind each and every technology but its good to know what you own or might own in future.

Lets understand each of them one by one.

1. Resistive Touchscreens

Basically, this touch screen (as the name suggests) would be based on some kind of resistance. If that came to your mind before I mentioned then you are good to go. Usually a resistive touchscreen is a made of a normal glass with 3 layers. The uppermost layer is non functional and mostly it is used as a protective layer to resist scratches and is usually Polyethelene (PET) based material to make it flexible. The next two layers are the contact layers and are conductive. These layers are coated with a metallic substance like ITO or the Indium Tin Oxide (ITO is popular for its electrical conductivity as well as for its optical transparency).

When the system is in action, current flows through these layers. To achieve a resistive response from this system, the two conductive layers are separated by spacers. These spacers are like tiny bumps(as shown below) that are added to the top ITO coating, that avoids PET film from sagging, causing accidental or false touch.

So when a finger touches the PET surface, it causes a sag and the two ITO layers get connected, causing a change in electrical field. This change in electrical field is sensed by the controller, goes as a feedback to the touchscreen driver to calculate the exact coordinate of the sag, the point of contact.

Pros:

  • Cheaper than Capactive screen.
  • Can operate with any pointing devices like stylus, pen, nail etc. Enhances handwriting recognition system
  • Humidity is not a problem
  • High accuracy in coordinate calculation.

Cons:

  • Multi touch is not supported although there are few reports of multi-touch support, but not on a large scale.
  • Highly sensitive, dust particles is a problem for this screen.
  • Light or no visibility under Sunlight, mostly due to multiple layers reflecting light.

2. Capacitive Touchscreens

In a simple capacitive sensing a finger acts as one of the conducting layer. For a matter of fact the Human body acts as a conductor and a huge sink. When a finger is touched on a capacitive sensor, few charges get transferred to the finger thus changing the total circuit capacitance. The change is then transformed to a coordinate and is passed to the system driver.

Pros:

  • Most suitable for multi-touch.
  • Very good visibility under sunlight.
  • Highly sensitive to finger touch.
  • Dust particles, grease, moisture, not a problemo!!
  • Glossy look and feel.

Cons:

  • Atleast 5% humidity to achieve capacitive effect, because capacitance is dependent on Di-electric constant which itself depends upon the Relative Humidity and Di-electric constant of moist air is more than air.
  • Very expensive.
  • Doesn’t work with inanimate objects/fingernails/gloved fingers.
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