Touch screens are used in a rich variety of new products: cell phones, computer tablets, personal navigation devices, MP3 players, digital cameras, fitness equipment, security systems, point of sale systems, and kiosks. Examples of consumer devices using projected capacitive touch screens include Apple’s iPhone and iPod.
Touch screen displays
A touch screen is a display that responds to user input based on touching a point or points within the display. 3M, Elo TouchSystems, and Planar Systems are well known for making touch screen displays. Displays range from 2 to 32 inches that are useful for consumer, retail, industrial, healthcare and transportation applications.
Resistive touch screens
One common technology for touch screen display is the resistive touch screen. When pressed the flexible top layer bends and completes an electrical connection. Because the top layer actually bends, the resistive screen is fragile and its multi-layered construction can reduce the optical clarity. Even though the resistive touch screen does have some drawbacks, its low cost makes it very attractive for many applications.
Capacitive touch screens
Capacitive technology offers improved optical clarity, damage resistance, and high signal-to-noise ratio. It uses capacitive sensor technology etched in an XY array of electrodes to accurately pinpoint selection. This is similar to the pixel grid found in many displays. It is possible to measure the capacitance change at every individual point by applying voltage to the grid. One disadvantage of the capacitance touch screen is that it works poorly when wearing gloves, which is common in some industrial applications.
Projected capacitance touch screens
A newer technology, projected capacitance is increasingly being used to create touch screen displays. By moving a finger or conductive stylus close to the surface, the sensor capacitance changes and accurately determines the touch location.
Unlike other types of capacitive touch technology, projected capacitive touch screens do not require contact and will work with a gloved hand or covered finger. Another advantage of projected capacitance touch screens is that they have less wear if you don’t need to touch the screen.
A couple of key technologies of the capacitive touch screens are the capacitive controller and the capacitive sensors.
Capacitive Controller ICs
Analog Devices, Altera, Atmel, Cypress, Freescale Semiconductor, and STMicroelectronics make product families of Capacitive Sensing controllers. Each organization offers a different number of channels, host interfaces, input voltages, self-calibration, auto-drift compensation, and IC packaging.
Capacitive sensors are typically custom designed for each application, since each device may have special shapes and sizes. These sensors may contain different mediums such as copper, Indium tin Oxide (ITO), and printed ink.
Touch screens have now been widely incorporated into a huge number of everyday devices. They will continue to be a growing area for innovation in electronic systems.
Touch Screen Project
On a recent project, Voler Systems used a 6.5-inch flat touch screen display integrated with a PC-compatible computer board with a small enclosure less than two inches thick. Voler Systems modified the embedded software to run on the new equipment. The customer makes equipment that controls temperature, flow, resistivity, and other parameters in semiconductor clean rooms or the adjacent equipment area, military installations, and other industrial applications. The compact size and touch screen operation was required for the machine to meet the NEMA4 standard, which means it can have falling water on it. In no case is it convenient to have a mouse or keyboard, so a touch screen is used.
If you have limited space and want to eliminate bulky displays, keyboard and mouse control for products, please contact us.
Walt’s Perspective on Touch Screens
LCD screens have become ubiquitous in all areas and all sizes of screens. Touch screen technology is easy to add to LCD screens, whether small screens for embedded applications or large 19-inch screens for PCs, making it easy and inexpensive to have touch screens wherever they are desired. People find touch screens to be valuable where a mouse and keyboard are impractical, for example in interactive displays in shopping malls, in hospitals, in industrial equipment, and in portable consumer devices. The mouse and keyboard are not going to be replaced by touch screens in office applications. I expect that we will see increasing use of touch screens in medical, aerospace, and industrial devices, where we have been using them in the past.