Touch Screen Technologies

Optical (Camera Sensor)

Optical techniques use an infrared light source to illumuniate objects which are then converted to points of interaction. The user(s) then manipulate a visible light screen that the camera can't see.

The most common techniques are:
Below is a video series that I made showing how to build each of the main optical methods.





Infrared Frames



NOW AVAILABLE on the Peau Productions Store. These thin frames have alternating infrared LEDs and infrared detectors which can track objects that obstruct the sensors normal view. In the past the frames have only been capable of single or dual touch, but recently multitouch drivers have been created. The frame is placed onto the touch surface, meaning that a thin bezel, usually no more than 1cm tall must exist. This means that you cannot have a flat top layer, like you can with other techniques like capacitive touch screens. The benefits though are that all the imaging is only done in a 1cm tall frame, and when compared to other thin technologies like capacitive films, are relatively cheaper. The main advantage over a camera based setup is that even though infrared light is still used to illuminate the objects being tracked, the touch frames perform much better in all ambient lighting environments.

Projected Capacitive Films

Capacitive touchscreens are layered with a material that continuously conducts an electrical field and creates a capacitance. When the human body, which also has its own capacitance interupts this field, the location is processed as a touch point. This technique can only work with human touch and not with gloved figners or styluses. It can do multitouch though, as can be seen on the Apple iPhone.

Resistive Films

The most commonly used touchscreen technology used today. A resistive touch screen is made of multiple thin layers that when pressed are connected via an electrical circuit which are processed as a touch point. It does not though support multitouch capability and is mentioned here since it is often confused with capacitive technology.

Surface Acoustic Wave (SAW) Films

SAW touchscreens use ultrasonic waves that are emitted from a clear mylar film, with microscopic wires running back and forth. If you look closely at the screen you will be able to see these wires. When something touches the screen the waves are absorbed and interpreted as a touch point. Typically only one or two touches can be detected, not multitouch. The benefits though are that you can adhere the film to the bottom or inside piece of material, such as a shop window and ambient light does not effect its performance.

There are many other touch screen technologies which you can read about here on Wikipedia.