Shayan Javed

Virtual Environments - Spring 2009 Project 1

Project: To demonstrate how different types of touchscreens work using a Nintendo DS as a placeholder and ARToolkit for augmented reality.
Download link: Project 1

Goal

Touchscreens are becoming more and more popular nowadays. The goal of this project is to show the underlying mechanics of 3 types of touchscreens: 1. Resistive 2. Capacitive 3. Infrared (optical) Some interaction will be possible using a finger and a stylus, to show how the touchscreens change as they are pressed.

Nintendo DS

The Nintendo DS is used as the device to show how touchscreens work. The lower-screen on the DS is actually a resistive touch screen. And the dual screens allow me to put a marker on the upper screen so that the touch screen is not occluded while interacting. For more information: Nintendo DS

Video:



ARToolkit Touchscreen demonstration
Uploaded by Shayan Javed

How It Worked

A marker is attached to the top-screen so that the touch screens can be projected at an angle to the DS's touchscreen. Both a touchscreen and a "regular" screen are displayed on the DS using AR. As interaction takes place on the touchscreen the regular screen also changes (to show where the user pressed).
To switch between the 3 different types of touchscreens, a simple "slider" was created which allows the user to switch. Depending on how far away this marker is from the camera the touch screen changes (denoted by a letter).

Interaction

Two more markers are used: one to show a finger and the other to show a stylus. The finger works for Capacitive and Infrared touchscreens. The styles works for Resistive and Infrared touchscreens. Interaction was probably the hardest part. The touchscreen resolution is extremely low (4 X 4 pixels in the middle) which is probably the biggest shortcoming. Detecting the exact position of these two markers and whether they are "near" the projected touch screen is not done that well but it sort of works. The lower resolution was used due to time constraints and to more explicitly show interaction. As a "touch" was detected, it showed the corresponding position on the upper screen. Normally the position would be detected on the touchscreen itself, but for clarity purposes a separate screen was used.

Resistive

Resistive touchscreens are made of several layers with two electrical conducting layers being the most important. As the user presses the upper layer a change in electrical current is detected and reported. The Nintendo DS uses a resistive touchscreen. They are widely popular and cheap. But accuracy is not the best, multitouch is not possible and they can scratch. They usually require a "sharp" object to interact with, so the finger gives no response but the stylus does.

Capacitive

Capacitive touchscreens have a thin layer at the top which stores electrons and has a charge. There are 4 circuits at the corners which detect the change in electrons. Since humans can conduct, as a finger gets near the screen it absorbs some of the electrons (denoted by moving yellow vertices in the video). The circuits detect the change in electrons and report the position. A regular stylus doesn't work since it doesn't conduct. The Apple iPhone uses a capacitive touchscreen. They are becoming more and more popular, are more accurate than resistive and can also do multitouch.

Infrared

Jeff Han popularized this type of touchscreen with his TED talk in 2006. Infrared rays are bounced between two acrylic sheets. As the user presses the sheet the rays are stopped from traveling, and a "blob" shows up on the lower screen. A camera (or multiple cameras) situated beneath the touchscreen detects the blob and reports the position. The Nintendo DS is probably not the best way to show how these work, since a camera is required to detect the positions. A virtual camera situated beneath the screen is shown in the video. IR touchscreens are highly accurate and can detect multitouch easily. But they require bigger setups to work since a camera is required (example: Microsoft Surface). In my project both the finger and stylus can be used on the IR touchscreen to demonstrated multitouch.