Experiments with Touch – Building a dual screen Surface Acoustic Wave Touch table

Posted on October 17, 2011

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Brief

The next Touch project on my list involves a Surface Acoustic Wave Dual Touch panel.

I am choosing this technology for the following reasons/advantages:

  1. Affordable multi touch – Capacative screens become increasingly expensive as size increases. SAW stays relatively low cost.
  2. Less vulnerable – I noticed with a capacitive Touch screen from [insert here] that it is prone to scratching
  3. Scalable – At NijTouch you can order SAW panels up to 42 inch. Resistive Touch Panels go up to 22 inch and apparenly it stops there for now, for the Business to Consumer market.
  4. No ridges/Flat surface – The alternative to SAW is Infrared Touch, but these “panels” involve a ridge on top of your touch surface to house the IR LEDs/Sensors

Possible disadvantages and limitations:

  1. Water and dirt – The SAW panels might be more subjective to water and dirt: acting as “touch shadows” casted by the dirt and water instead of by your fingers. I will have to test that. As SAW is used for more “prone to abuse” type of use like: “ATMs, Amusement Parks, Banking and Financial Applications, public information kiosks” I think it might be fine
  2. Latency & precision – Also I do not know what the latency and precision is.

Application

The application I have in mind is for table-based Touch Surfaces, like in a cafe or in your home. The main goal is to have a multi-touch surface that can deal with the stress and abuse of day to day use of objects placed on the surface.

The alternative

The alternative I might fall back to for the final product is Resistive Single Touch.

Surface Acoustic Wave Touch (SAW)

From TVI Electronics :

The Surface Acoustic Wave (SAW) technology is one of the most advanced touch screen types. The technology is based on two transducers (transmitting and receiving) placed for the both of X and Y axis on the touch panel. The other important element of SAW is placed on the glass, called reflector. The controller sends electrical signal to the transmitting transducer, and transducer converts the signal into ultrasonic waves and emits to reflectors that are lined up along the edge of the panel. After reflectors refract waves to the receiving transducers, the receiving transducer converts the waves into an electrical signal and sends back to the controller. When a finger touches the screen, the waves are absorbed, causing a touch event to be detected at that point.

Compared to Resistive and Capacitive technologies, SAW technology provides superior image clarity, resolution, and higher light transmission. Because the panel is all glass, there are no layers that can be worn, giving this technology the highest durability factor and also the highest clarity. Disadvantages of Surface Acoustic Wave (SAW) technology include the facts that the touch screen must be touched by finger, gloved hand, or soft-tip stylus (something hard like a pen won’t work) and  that the touchscreen is not completely sealable, can be affected by large amounts of dirt, dust, and / or water in the environment.

The Surface Acoustic Wave technology is recommended for ATMs, Amusement Parks, Banking and Financial Applications, public information kiosks, computer based training, or other high traffic indoor environments.

Surface Acoustic Wave itself apparently is a process/theoretical principle already discoverd in1885. Read the Wikipedia article here. Touch screens are briefly mentioned in that article:

SAW sensors have seen relatively modest commercial success to date, but are commonly commercially available for some applications such as touchscreen displays.

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