Why you need to use capacitive touch panels in your GUI design
The range of embedded systems where the operator interface might be based on PCAP display technology is certainly broad.
On one hand, the sleek and compelling look and feel of a PCAP panel is compelling for designers of systems for consumer-oriented products like navigation systems, home and automotive infotainment systems, even household white goods like washing machines and microwave ovens.
On the other hand, PCAP displays have many compelling qualities for the designer of embedded industrial systems. These include their rugged durability and the versatility of their construction which makes them adaptable to a wide variation of environmental conditions such as extreme heat and cold, intense sunlight, wear and tear from repetitive touch patterns on the screen and others.
Many medical systems provide an example of the types of embedded applications that benefit from PCAP display panels. For instance, patient monitoring units for hospital nurses could be equipped with a PCAP display.
One touch might freeze the display, while a second single swipe on the screen could quickly move back in time and a third tap on the screen could restore the display to the current conditions.
A touch panel with two-finger touch capabilities would allow two interactive cursors to be used to set alarm limits. And two-finger gesturing could implement time compression and expansion. Or, a PCAP display on an ultrasound imaging system might replace the keyboard and roller-ball that typically function as the user interface.
Of course, medical systems have stringent requirements. To combat blood-borne pathogens and other sources of disease and infection, all electronic systems including the user interface must be tightly sealed in their enclosures. Bacteria-breeding moisture must not be able to accumulate in grooves or inside enclosures.
In addition, the cleaning requirements for hospitals dictate that all surfaces must be durable enough to withstand the cleaning fluids. It is quite common for these fluids to contain as much as 10 percent bleach.
To meet these requirements, PCAP displays can be hermetically sealed to keep germs and moisture out and they can be optically bonded with highly impervious materials, such as glass, to protect against chemical solvents and cleaners. Moreover, a PCAP display can be deployed as a completely flat surface with no grooves or notches where bacteria and germs might congregate (Figure 2 below).
Figure 2. PCAP displays are completely flat surfaces with no grooves or notches within which bacteria and germs might congregate.
Other critical requirements of medical systems are impact resistance and non-sharding, just in case breakage occurs from extreme impact. In the typical hospital room there are many projecting arms with hooks and other types of sharp-edged fasteners.
It is quite common for a piece of equipment to be accidentally bumped or suddenly pushed aside in an emergency. As a result, every display panel in the room must be able to withstand significant impact.
The hospital industry’s standard for nurse call equipment, UL 1069, specifies that a display must withstand the impact of a ball drop test to 7 Joules. Again, a PCAP display panel can be housed in an enclosure made of a protective material without suffering significant degradation of the optical quality of the image on the screen or its touch-sensing capabilities.
The non-sharding requirement is similar to that of the automotive industry. Even though the chances are remote, the glass on a display panel in a medical setting could be struck with a force great enough to break it.
If this were to happen, the glass cannot shard into tiny splinters of glass that could harm someone. PCAP display panels from some vendors already meet this requirement.
Of course, the nurses, doctors and technicians who operate medical equipment often wear latex gloves. In operating rooms it is common for doctors and nurses to wear two pairs of gloves just in case the outer glove is punctured.
This means that a PCAP panel must be able to sense a change in capacitance on the surface of the panel despite the insulating latex covering the fingers. This degree of sensitivity has been achieved in PCAP panels that are currently being deployed in medical systems.
Product designers need to appreciate the complexity of developing and tuning a PCAP panel to perform in certain environments with unique enclosures and coverplate materials. It is important for designers to understand that there are many variables that need to be addressed to ensure that a touch panel will perform satisfactorily and will meet the design requirements for a particular application and/or environment.
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