Military Touchscreen Challenges | Baanto - Delhi

Even under the umbrella of the military, there is a multitude of sub-environments that offer unique challenges over and above the broader ones.

Military Touchscreens
When it comes to military environments, one issue arises repeatedly; viewability. The need to have the maximum clarity and purest blacks is often a key demand. So how does this impact touchscreens? Well, most touchscreen technologies, aside from IR, require some sort of coating on the surface of the touch interface, or glass that can affect the degree of light transmission. Ah yes, you say, but military displays almost always need some sort of coating anyway, don’t they? Well yes, this is indeed often the case. However, the layers needed to make the touchscreen operate are typically thicker and less optically pure than the specialized filter lays used by the military. For example, the ITO layers used in PCAP touch components can reduce optical transmissibility by up to 30%. Touchscreens that use pure glass are the option to be considered when clarity is a high priority. These are typically traditional IR, and they present their own challenges.

Apart from optical considerations, there are other parameters that become key in military equipment. Depending on the operational environment, there can be EMI interference, ambient light issues and mechanical noise/vibration to be concerned about. Overall reliability is a big concern, of course. NVIS compatibility is often a factor too and can be very challenging when it comes to the newest versions of NVIS devices.

Capacitive and Projected Capacitive (PCAP) Touchscreens
Capacitive and Projected Capacitive (PCAP) touchscreens can address many of the reliability concerns, of course, and they are highly accurate and responsive to touch, requiring zero touch force. They are not susceptible to ambient light overload, and they are entirely solid-state and therefore less likely to suffer from mechanical shock and vibration issues. However, they rely heavily on electromechanical coatings, and so are subject to concerns relating to screen image clarity. A typical PCAP touchscreen, for example, is made up of a large array of indium tin oxide (ITO) conductors on multiple layers of glass or polyethylene terephthalate (PET) plastic. [Figure 1]

PCAP touchscreen layers example
Figure 1. PCAP touchscreen layers



In this example, at least five layers have been added between the display and the viewer. Whilst the ITO layers have reasonable optical clarity, they do affect display quality, and may even affect viewing angle. Each of the fine ITO layers is made up of semiconductor material and has the effect of blocking out some degree of light. Think of them as the bug screen on your window, you can see out with the screen in place, but it is blocking 30 – 50% of the light. Additionally, layers of insulation may be needed to attempt to mitigate electrical noise, adding more complexity and giving rise to distortion of the image on the display. [Figure 2]

PCAP insulation layer touchscreen-example
Figure 2. PCAP insulation layer

PCAP touchscreens are also sensitive to electrostatic noise and interference. Despite many methods used to dampen or remove the effects of electrostatic noise, the fact remains that the almost invisible matrix used to sense touch is also akin to a big antenna array.

Resistive Touchscreen Technology
Resistive technology is often used in various touchscreen technologies. Resistive can be less expensive and is reasonably accurate and responsive. Whilst this type of technology has improved over the years and has been used in various military applications, it shares many of the disadvantages of PCAP, and adds a few of its own, however.

For example, resistive screens require a certain amount of activation force, typically 60 – 80 grams. Whilst this may not sound like much, if being operated by a gloved finger, considerably more force is required to compensate for the compression of the glove material. This need to be sure to press hard enough raises response times and makes room for errors. Resistive technology uses layers in a matrix in much the same way that PCAP does. However, even the best quality resistive touchscreens need more layers than their capacitive counterpart, meaning even more light is blocked as it passes through the device. [Figure 3]

Resistive touchscreen layers example
Figure 3. Resistive touchscreen layers

Not only is optical clarity more compromised, but there are also now more layers to potentially fail. This technology also relies on an electrical matrix to function and therefore suffers from the same potential for electrostatic interference as PCAP. Resistive screens are also prone to single-point failures. That is to say because mechanical force is needed to make a contact, repeated operations in any given location can possibly cause a failure at that point.

InfraRed Touchscreen Technology
InfraRed sensing has been around for decades. Beam-break touchscreens (traditional IR) are very effective and do not require anything more than a sheet of glass as a touch surface. IR touchscreens can be very responsive, and they are also less expensive to manufacture. At its simplest level, it is one IR light source, and one IR sensor or receiver. [Figure 4] This setup creates a beam that, if broken by something passing through it, triggers a circuit.

Infrared touchscreen example
Figure 4. InfraRed touchscreen example

By creating a matrix of such beams in both X and Y orientation, you can now sense the point of touch, as shown in figure 5.

Beam-break-touchscreen-example
Figure 5. Beam-break example

However, traditional IR touch screens suffer from significant issues and limitations that make them a less than perfect choice for a high-reliability environment. Among these are their susceptibility to external lighting conditions. Infrared light can be found in sunlight and from many other sources, for example, and when such “stray” IR enters the touch screen, it can cause false readings and ghost touches. Attempts can be made to minimize this by adding a douser or cover (see Figure 4) over the IR receiver, kind of like a sunshade, but this has a limited effect. In a high-flying aircraft cockpit, for example, the sunlight will shine brightly through the glass and will reflect off of many surfaces.

Another problem with IR beam break is limited resolution. Because you need pairs of light sources and receivers, these components have a finite size and also need to be mounted onto the PCB. This means that resolution is limited to the spacing of the components. There are also implications for reliability. If any one light source or receiver fails, particularly in a critical location, the touchscreen will fail to work as required.

So, is there any one solution that can minimize the potential problems of the technologies above?

As we all know nothing is perfect, but one solution, ShadowSense by Baanto International, overcomes many of the issues presented by other technologies

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