Just on a Touch! - Mobile Phones with Touch Screen

Am pretty late to blog about the touch screens - Almost 1 year! As part of my job, i had to investigate few behaviors of touch UI. When decided to get into the details of touch UI, the first thing came in to my mind was my iTouch. It works great for me unlike one another touch phone I have. I digged few details from How Stuffs Works.com to figure out the inner working details of iPhone Touch. The following are the facts i got from the site.

• iPhone Employs Capacitive touch technology and has a new arrangement of the capacitors compared to other devices. The capacitors arranged according to the coordinate system. Its circuitary can sense the change at each coordinate along the grid and generates its own signal. These signals are relayed to the processor and the processor software is able to determine the movement and location of simultaneous touches in multiple locations.

I became more curious to know how the underlying hardware work in various technologies to make this all happen

Capacitive Touch Detection

A basic capacitive touch panel consists of an insulator such as glass coated with a transparent conductor such as indium tin oxide (ITO). As human body is also a conductor, touching the surface of the screen results in distortion of the local electrostatic field, measurable as a change in capacitance. Different technologies may be used in determining the location of the touch.

I got an image from one another site that explains the capacitor creation and some more explanation of it.

The ITO layers are sealed between two glass sheets. The patterns on the two ITO layers form a grid of capacitors. The electric field of these capacitors are projected through the top layer of the glass. When user places a finger near the top surface of the touch screen, it couples with the electric fields. This coupling changes the capacitance of several of the capacitors in vicinity of the finger. An algorithm converts these changes in capacitance into a location along the X and Y axes of the screen.

Surface Capacitance

In this basic technology, only once side of the insulator is coated with a conductive layer. A small voltage is applied to the layer resulting in a uniform electrostatic field. When a conductor such as human finger touches the uncoated surface, a capacitor is dynamically formed.

SideTopics

While browsing through various sites, found an amazing link at http://multi-touchscreen.com demonstrating multi touch interface.

Some Extra Items

• ITO is used because the substance is a transparent conductor. The dielectric to form a capacitor is actually air it looks like.
• Touching the screen with a thick glove will not cause the change in the electric field and hence the capacitance will not vary and because of this, the touch sensing cannot be done. Usually in such situations, the sensitivity of the screen will be increased.