One of the major components of many interactive exhibits is a touch screen. We routinely work with a variety of touch screen types and technologies at Boston Productions. Without firsthand experience it is difficult to know which technology works best for a given situation. The process of purchasing and implementing a screen that will be used by thousands of people a day is also a bit of a mystery unless you have done it before. You’re in luck because I am going to provide a firsthand overview of each technology I have worked with and common mistakes made while implementing them.
About Purchasing Touch Screens
Usually the big monitor manufacturers such as NEC and Samsung don’t actually make touch aware systems. When purchasing touch monitors you usually buy them from a company that purchases a monitor and modifies it by adding touch capability after the fact. This adds to the complexity of purchasing because you need to make sure that you are initially getting a good monitor, but are also working with a competent touch screen integrator.
The Types of Touch Systems
Capacitive – Capacitive touch screens work by sensing small changes in the electrical pattern over the touch screen surface. Your skin creates small electrical connections, and the touch screen software can interpret these to know exactly where your finger is located. Skin, or another conductive material is needed to make capacitive screens work properly. Using a stylus or other pointing device will not work. For instance, the iPhone touch screen is a capacitive screen.
Resistive - Resistive touch screen work by sensing any pressure by any object. It contains a couple layers of sensors and materials. There is a thin layer of a similar material that is the main part of the capacitive screen. It will detect small connections made when contacted by a conductive material. In this screen though, there is another layer of this conductive material that is very thinly separated from the capacitive layer. By touching the screen, you’re pressing down to create contact between the layers, and registering a touch with the computer. Many devices that use a stylus are resistive screens like the bottom screen of a Nintendo DS, or Palm handheld devices.
SAW – Surface acoustic wave is based on sound waves traveling across the surface of the touch screen. When they are disrupted, the sensors know where you have touched. For the programmer, a SAW screen can emulate a mouse just like you would expect it to. The SAW technology is what we prefer and use on most of our systems.
Infrared – Infrared is usually based on IR LED’s close to the surface of the screen coupled with cameras that can detect where the IR beams are being disrupted. You normally can purchase an IR overlay as a completely separate piece of equipment from your monitor and install it on site. These are commonly used on larger screens where other technologies become less accurate. For instance, making a capacitive screen that is 40 inches is very difficult, so often an IR overlay is used. Often, this detects when a finger or other object breaks the plane of the IR beans, so you can sometimes operate an IR screen without actually ever touching the screen.
DST – Dispersive signal technology is based on sensing changes in the mechanical energy happening on the surface of the screen. You can touch the screen and it will recognize it as a click, but if you continue to hold your finger down, without moving, this type of overlay will think you are no longer touching it.
An advantage of this technology is you can have items already sitting on it, and if they remain stationary; touch functionality will be unaffected for the rest of the screen. This situation works best for touch screens that are integrated into work surfaces that you could benefit from allowing stationary items to rest on the screen.
Remember that with this technology it is not possible to accurately or consistently touch and hold items while remaining stationary.
Although they may seem very similar, each type of technology requires different care and consideration when implementing.
Proper ventilation is always needed when using touch screens. You will often find that when a monitor overheats you lose touch intermittently or altogether. This usually means purchasing 80mm fans and installing them in your monitor enclosure.
Be very careful with the bezels of monitors and area directly around the touch surface. We routinely work with fabricators that love to cover up the bezels of a touch monitor. When this happens it’s imperative that these covers are not putting pressure on the bezel of a touch screen, or are physically contacting the touch surface. When this happens you normally end up with a non functioning touch screen.
If covering the IR sensor for a monitors’ remote, have the fabricator drill a small hole so your remote does not become useless. It’s always handy to be able to use the remote even with a touch screen.
Technology Specific Considerations
DST – In my experience with DST, I worked on several large monitors that were to be mounted vertically. Due to the way that DST works, you have to be extremely careful when mounting
the monitor not to put any pressure on the screen or bezel. Because it works based on mechanical energy, if you apply pressure from your mount on one area of the screen more then another, your touch overlay will become biased in one direction. The result of this biasing is that you have a touch overlay that is more sensitive in one area then the other, or completely unusable.
SAW – Just make sure that you don’t have anything else touching the overlay when you implement it. Also make sure to clean the monitor surface semi-regularly.
Infrared – With infrared, just make sure you don’t have debris blocking any portion of the IR LEDs or their associated cameras’. An example of a debris that is pretty common is packing material. If using an external overlay that you strap to the monitor, make sure that the overlay is very snug against the side edges of the monitor so that it will not move when mounted. Many external IR overlays can conceptually be imagined as a picture frame.
This is meant as a brief overview of touchscreen technology, and a starting point when trying to determine which type of screen is right for you.