LCD Touch-Panel Controllers
Jan 1, 2003 12:00 PM, Chris Steinwand
As daily life becomes more dependent on technology, customers and clients are looking for improved ways to interface with the many devices that surround their homes and workplaces. Found nearly everywhere — on ATMs, on transit ticket machines, at grocery checkout stands, on interactive museum kiosks, or even as entry points for access control or security systems — LCD touch panels offer an intelligent, high-tech solution.
FORMS, FUNCTIONS, FEATURES …
A touch panel turns a flat-panel display into a dynamic graphical user interface (GUI) and data entry device: with its touch screen representing a replacement for the keyboard and mouse — or, in some applications — a stack of remote controllers. All LCD touch panels operate on the same basic principles, which is to say that they register a contact closure of a certain value and transmit that information — through serial cable, Ethernet, infrared (IR), or RF — to another unit that then takes the appropriate action(s).
Touch screens come in a wide range of styles, from full-color VGA and SVGA monitors designed for highly graphic applications to small monochrome displays designed for simple keypad replacement. The applications of these devices are equally broad. Many touch-panel controllers offer customizable dynamic screens, dedicated push buttons with multiple functions, and a full range of other input options. On most models, graphics can be used to provide visual prompts, examples, or warnings. Text can be displayed in several languages, if required. Another advantage? As equipment and applications change, screens can be quickly updated to meet new requirements. Aside from being easy to use and more modern (read: high-tech) in appearance than a standard keyboard and mouse, touch panels often provide a more durable interface. Some even incorporate features such as waterproofing or scratch resistance.
Beyond the obvious function of eliminating keyboards and separate data entry devices, touch panels should offer an intuitive interface. Buttons on the screen can be represented by text, images, or a combination of both. Once the initial programming is completed, operation of the touch panel is usually easy, with a short learning curve. The user simply touches one of the virtual buttons to execute a command or series of commands. Going one step further, the screen on the touch-panel controller can be customized to present only the valid options for each phase of an operation, greatly reducing the frustration of trying to find the right key or combination of keys to perform a particular task.
It's also important to keep in mind that two controllers with identical functionality can have completely different looks to suit the application. People associate actions or functions with a visual image better than a combination of keystrokes or button presses. Using a touch panel is more entertaining for the operator and actually requires less brainpower than traditional controllers, which could explain the proliferation of touch-screen interfaces in fast-food and retail establishments.
The touch panels themselves are based around four basic screen technologies: resistive, capacitive, IR, and surface acoustical wave (SAW). Each of those designs has distinct advantages and disadvantages; some understanding of the background technology will help you determine the type that's best for any intended application. Note: many of these are designed to comply with specific National Electrical Manufacturers Association (NEMA) standards to meet various installation requirements. For more information about NEMA standards, visit www.nema.org.
RESISTIVE SCREEN TECHNOLOGY
Resistive touch screens embed a thin glass substrate between two layers of a plastic overlay. The surface of the glass substrate has a tin oxide coating onto which a slight electrical current is constantly applied. The plastic overlay and the glass substrate are separated by hundreds of microscopic dot separators. When pressure is applied to the outside of the overlay, the two surfaces touch and a ground occurs. These essentially act as contact closure devices. The x- and y-coordinates of the ground (touched area) are detected and registered with the control device, which then issues the appropriate command. A standard keyboard operates in much the same manner.
With resistive screens, any pointing device can be used. These systems can be washed down and are able to meet ratings for NEMA 4/4X and Class I/II, Division 1/2 with intrinsically safe barriers (read: medical applications). Drawbacks include the potential for damage (cuts) to the plastic overlay from sharp instruments and a reduction in display brightness because of the overlay. Resistive screens are the most popular form of touch-screen technology in industrial applications and account for all but one of the touch panels spotlighted in this article. Coincidentally, this type of touch screen is also the least expensive and easiest to use.
INFRARED SCREEN TECHNOLOGY
In an infrared screen, miniature transmitters are located across two nonopposing sides of the mounting bezel. The transmitters emit IR light beams from top to bottom and right to left with receivers located on the opposite sides to form a grid pattern across the screen. When an object, such as a finger or stylus, interrupts the beams, the x- and y-coordinates are detected.
IR touch screens provide good clarity, because they don't have the layers of plastic overlay. They allow the use of gloved hands or other triggering apparatus. In addition, they can meet ratings for NEMA 12/4 and Class I/II, Division 1/2 with purging. However, they may not be suitable for direct wash down because of the IR diodes located on the outer bezel. They can also be activated by debris falling on the display surface if it disrupts the beams.
CAPACITIVE SCREEN TECHNOLOGY
These screens use a glass substrate with a tin oxide coating that is charged with a slight electrical current. When a conductive stylus or finger touches the surface, it creates a capacitive coupling that causes a current draw at that point. The x- and y-coordinates can then be determined in much the same way as with the resistive technology screen.
The glass substrate of a capacitive touch screen is resistant to scratching, and the touch-screen system can be built to NEMA 4/4X standards. One drawback of this technology: gloved fingers will not activate the screen surface, as it requires a conductive pointing object. On occasion, this system can also be fickle; if an operator remains in one position while executing several commands on the touch panel, that person's capacitive charge (or discharge) can lower to a point where the screen has difficulty registering the touch.
SURFACE ACOUSTICAL WAVE TECHNOLOGY
Beyond having the most impressive-sounding name of the four types of display technologies, SAW also provides the highest resolution on the screen surface. With surface acoustical wave technology, a set of transducers emits an acoustic wave across the horizontal axis and vertical axis through reflective arrays. Receivers on the other side pick up the flow of the waves. When the surface of the screen is touched, a disruption in the wave occurs, and the controller software determines the x- and y-coordinates.
SAW touch screens are durable and allow the use of gloved hands. However, they can be built only to NEMA 12 standards, which means they cannot be used in medical applications. They can also be activated inadvertently by any dirt, grease, or liquids that fall on the surface. One touch panel listed in this article uses this technology; it claims to have built-in software management that detects foreign objects that fall on the screen and prevents it from registering false commands. By analyzing the new repetitive pattern, the unit actually “sees” the foreign material as part of the screen surface.
PRESENT AND FUTURE
In researching this article, I've explored the gamut of styles in touch-panel/screen styles, though realistically, there are fewer models available than one might expect. Costs have dropped dramatically during the past few years, yet touch panels are still relatively expensive. They also usually require custom programming by a system integrator prior to use, so they are not an off-the-shelf or plug-and-play item. Rather than looking at wallmount LCD screens and PDAs, I've targeted products that are typically used in pro A/V and boardroom applications and that can sit on a desktop. Here, listed alphabetically by manufacturer, is a sampling of what's available in 2003.
The NXT-CA15 touch panel from AMX is available in tabletop or wallmount versions. It has a 15-inch color active dot-matrix screen capable of displaying 16 million colors at a resolution of 1,024 by 768. It can be programmed with extensive graphics and text. It has a 10/100 Ethernet port for connectivity, with optional IR capability. The unit has a built-in microphone and speakers for easy desktop conferencing. It is available in a black matte finish with a platinum-colored bezel trim. The CA15 also has features like a motion sensor that automatically wakes up the unit when it is approached. In addition, an optical sensor adjusts brightness automatically.
AMX's NXT-CA12 touch panel is essentially a smaller version of the CA15. With its 12-inch color screen and 800-by-600 resolution, it has the same programmability and the same built-in templates as its older sibling. Both of these units also have a Sleep Mode button, which puts the unit to sleep or wakes it up. An included breakout box provides both units with audio/video distribution and accepts composite or S-video inputs. Smaller yet is the AMX AXD-CV6, a 6-inch color active dot-matrix display with 320-by-240-pixel resolution. Like its larger cousins, it can display NTSC or PAL video. Available in white or black, the AXD-CV6 can be wallmounted or installed in a tabletop kit that provides a combined Axlink (4-pin serial connector to AMX controller) and video feed from the unit.
Crestron's Isys TPS-6000 is a completely self-contained touch-panel system. It has a 15-inch full-color screen that displays full-motion NTSC and PAL video at 256,000 colors. Graphic display of control templates is in 64,000 colors. The unit's open architecture operation is capable of controlling any device through Ethernet, serial connection, or contact closure. Among its built-in features are a mic, speakers, and upgradable memory to store Web pages or play back WAV audio files. The unit comes with a 10/100Base-T Ethernet connection and an RS-232 port, and it has an RF option for wireless control. It supports dynamic and static IP addressing. Once it's plugged in to your Intranet, accessing other devices can be accomplished by navigating through a browser or through custom templates.
Crestron's TPS-3000 puts the same performance as the TPS-6000 in a smaller package. It has a 6.4-inch active-matrix display with 640-by-480 resolution; 64,000 colors; 8 MB of Flash; and 8 MB of DRAM. Like its sibling, it supports real-time video and can accommodate balanced or unbalanced signals in S-video or composite format. It supports NTSC and PAL, with adjustments for brightness, contrast, hue, and saturation. Audio capabilities include mic, stereo speakers with built-in volume control and WAV (8-bit/8 kHz mono PCM) file sound capability, balanced line-level stereo input through TPS-IMC/IMW with internal volume control, two speakers, and rear mini headphone jack.
Another Crestron offering, the STX-1700C, is a one-way wireless RF touch panel providing the user customized command of the system or environment. The handheld unit operates up to six hours on a single battery charge. It can also be operated from its docking and charging station. It has an operating range of as much as 300 feet, allowing complete freedom of movement and location. Five programmable push buttons on each side of the panel offer one-touch control over a variety of functions. The screen is a 5.7-inch, active-matrix color display with 320-by-240 resolution. It has 4 MB of Flash memory (at least 3 MB are for user display lists), 8 MB of SDRAM, a mini headphone jack, a 12V power jack, and an RS-232 port.
Distributed in North America by Aviscel, Cue Company's Guide Model CS0179 is a complete RF wireless control system. It includes a battery-operated RF mini touch panel with a 5.8-inch, 320-by-240-pixel color LCD. Its control panel comes in a black housing and is battery operated for handheld use, or it can be operated from the docking and charging cradle. The base unit is hardwired to the control unit, which has bidirectional RS-232 and RS-422 serial ports. The default RF frequency is 433 MHz, but alternative frequencies can be specified when ordering the unit.
Also from the Cue Company is the touchCue 99 (model CS0159) panel, which has a 640-by-480-pixel, 10.4-inch color LCD. Its open architecture allows programming multiple functions into single button presses. The panel is compatible with all Cue control units. User application screen layouts containing buttons, bar graphs, logos, drawings, and so on are prepared on a PC and downloaded into the touch panel. The touchCue 99 is available in standard black or in a real wood and stainless-steel enclosure.
The Elo TouchSystems 1000- and 3000-series touch-panel controllers use what the company calls IntelliTouch technology, which incorporates surface wave technology with a glass faceplate for high durability. Because the units use surface wave technology, they can be activated by a gloved hand or other noncapacitive devices such as a stylus or pencil eraser head. Part of the 1000 series, the Elo 1524L has a 12-inch active-matrix color screen with 1,024-by-768 resolution and 16.7 million colors. It has a serial control interface and can serve as a front end for any serial controller. The units sit on a detachable base and are also available in 15-inch screen versions — the 1525L and 1527L models — in beige or gray.
Although its primary function is to replace the plethora of IR remotes found in home-entertainment installs, the Lexicon 700t system controller is equally at home in a boardroom. Its LCD touch screen is a programmable GUI with a 5.6-inch monochrome display. A variety of predesigned templates are included, or users can create custom bitmap displays. Programming the 700t is usually done by the installer or system integrator using a PC laptop. The unit also has the ability to “learn” and then transmit as many as 64 commands with the touch of a button. For example, if you pushed the Watch a Movie button, the 700t could send the commands to turn on the video projector, lower the projection screen, turn on the audio system, start the DVD player, dim the lights, and mute your paging system so you won't be interrupted while watching your movie. The 700t can send signals through IR or RF and operates as much as six hours continuously on a single charge, which translates into several days of use under normal conditions. The unit can also be operated while connected to its recharging power supply. The 700t has an optional TCM-3 IR/RF to serial converter for hardwired control over equipment. In addition to an RS-232 serial port, the TCM-3 has three built-in relays and two power sensor inputs. The box is small and is designed to be mounted on a shelf or wall.
MORE TO COME
As demand increases for automation and other applications for touch-panel controllers, so will the product offerings. As you've seen in other areas of electronics, the costs of touch-panel systems will most certainly decrease in the years to come. However, one thing is certain: with the prominence of automation in people's daily lives, you'll be seeing more and more applications of touch-panel technology.
Chris Steinwand is a marketing veteran of the pro-audio/video industry, a freelance writer, and the director of Stonejam Consulting. You can reach him through e-mail at email@example.com.
The Panel PC Alternative
In addition to dedicated touch-panel products, panel PCs (PPCs) can also be used for control applications. These units are actual personal computers, housed in special packaging and equipped with touch screens. They have all the functionality of dedicated touch-panel controllers with the versatility of a PC. Panel PCs are generally more bulky than dedicated control panels yet offer many more features than their dedicated counterparts. Here are a few examples of PPCs.
The Kiosk, from Acme Portable Machines, is a PIII/Celeron-based panel PC, featuring an embedded MPEG engine, a 3-D graphics controller, and up to 64 MB of video memory. The Kiosk comes standard with a 12- or 15-inch TFT LCD, with optional touch screen (resistive, capacitive, SAW). Acme's K-Open is an industrial-grade, open-frame design with a 12.5-, a 15.0-, an 18.0-, or a 19.1-inch display. It has several mounting bezels; options include VGA and composite TV-out (RCA jack) ports that support mirroring and multiple dual-display modes.
The UltraSlim panel PCs from Advantech come in two sizes. The PPC-S153T has a 15-inch touch screen; the PPC-S123T is offered in a 12-inch package. Both are low profile for panel PCs, which are typically a bit bulky for tabletop applications. The two have resolutions of 1,024 by 768 and 800 by 600, respectively. Other features common to both are resistive technology screens, a PS/2 controller interface, two serial ports, a parallel port, and four USBs.
Heisei's LaVenus-series panel PC has a 15-inch touch-screen display with 1,024-by-768 resolution. The touch panel is offered in a choice of resistive, capacitive, or acoustic wave technology screens. It has a 10/100Base-T Ethernet port as well as four serial, one parallel, and two USB ports. Poseidon is Heisei's PIII/Celeron-based panel PC, in either 15.0- or 12.1-inch screens, with the same capabilities as the LaVenus series, including the touch-screen options of touch screen (resistive, capacitive, SAW). Poseidon has built-in speakers and comes in desktop tilt stand, wallmount, and swing-arm-mounting versions.
Spire Controls' SM1520 panel PC is an industrial-grade Pentium 4 system with a 15-inch LCD and touch screen. Designed with built-in Ethernet, USB ports, and a CD/RW-DVD drive option, this panel PC is suitable for Windows NT or 2000 OS platforms, and its 2 GB of onboard RAM handle most any application. Its P4 motherboard gives the SM1520 the fastest processor of the units in this article, though all of the panel PCs listed have more than ample processing power for control applications.
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