Touch-sensitive surface
A touch-sensitive surface is a flat sensor that can sense the position of a touch from a finger in a grid.
The term multi-touch is used when the device is able to interpret more than one touch point simultaneously.
Touch-sensitive surfaces have been used in a multitude of different types of input devices. The most common are the touch screen and the touchpad. Some mice have a touch sensor instead of a scroll wheel.
There are also touch-sensitive buttons using similar technology in some touch keyboards.
Technology
The most common touch-sensitive technology is capacitive sensing. Capacitive sensors depend on the electrical properties of the user's fingertips.
Capacitive touch sensors have the drawback that they are unable to sense gloved hands or traditional plastic styli, and this can especially be a problem for mobile devices when used in cold weather. The market has adapted to this, though. These days, there are several styli available with capacitative properties. There are also special "smartphone gloves" with capacitative fingertips. Previous to these products, there have been reports of people carrying uncooked sausages in their pockets for use as styli in cold weather[1].
Capacitive sensor technology has the advantage that multiple simultaneous points can be detected. This has led to the introduction of multi-touch trackpads and displays.
Prior to touchscreens, capacitive sensing was used in capacitive keyboard switches. Topre switches continue to use this method today.
Some other sensing technologies are:
- Resistive
- The surface needs to be pressed down. Common on older pen devices and on cheaper touch-tablets. Resistive panels can be prone to jitter, as seen on Psion's range of palmtops.
- Light beams
- Used by NeoNode devices (the ones that have prior art on slide-to-unlock).
- Gyro sensor
- Used primarily for touch screens, these sense when and how the screen is nudged when pressed (very unusual and primitive).
Touch sensors often have relatively low resolution. Touch-points on a screen should therefore not be interpreted as a point but as a circle or ellipse.
Stylus sensing
Some touch-sensitive devices also allow precision input from a stylus.
Some graphics tablets are also able to sense touch, being combined touchpads.
There are also touch screen devices that also allow styli. Some integrate a fully-fledged graphics tablets having separate sensing of finger and stylus. Others (such as Lenovo's "AnyPen") that don't discriminate between implements are usually regular touch screens with a higher sensor resolution than the norm.
A related technology is the light pen. The classic type of light pen works only on a CRT display, as it senses when the electron beam passes over the point of contact.
Feedback
Some touch-screen interfaces such as Microsoft Windows draws a circle to indicate each finger, making the user aware that the touch has been recognized by the system regardless of whether it has been recognized by the target application or not.
Some touch devices are able to provide haptic feedback in response to user through vibration. Apple's "Taptic"TM vibrator technology provides a sensation of click when pressure is applied to the screen or touchpad. See Haptics
