Limitations placed on which switch can be used due to its size, often exclude the option of using the "right" switch with the most advanced technology.

By Hassan Sajadi, NKK Switches

Does Miniaturization Really Matter?
Figure 1.)
In today's love affair with ultra-subcompact devices, it is easy to succumb to the temptation of thinking that smaller is always better. From laptops to cell phones, the decreasing size of wireless digital devices is resulting in not only smaller interfaces, but smaller switches on those interfaces, which is not necessarily a good thing — something that anyone who has tried to make an urgent phone call or type an e-mail on a Blackberry's tiny buttons can tell you after they have reached the wrong number or made an embarrassing typo. And, when you stop to think about it, the iPhone is just a giant touch screen switch that makes phone calls. In this case, a bigger switch is very important.

It is true that smaller often is better than a big, bulky device that takes up precious room and gives you a workout every time you take it out of its case or raise it to your ear. Engineers are often obligated to incorporate smaller switching devices due to circumstances beyond their control, but there is more to consider than just miniaturization when laying plans for the switches to be incorporated into a wireless device. When considering switches for an interface, it is important to weigh several crucial factors of switch design against miniaturization simply for its own sake.

Advanced Technology
Does Miniaturization Really Matter?
Figure 2.
Many times, the smaller a switch is, in all likelihood, the less functionality and more simplistic it has to be. The issue is that limitations are put on which switches can be used, often excluding the option to use the most advanced switches which would greatly enhance the capabilities of the overall interface.

Take for example "smart" switches, or programmable switches, that combine two important switch options: dedicated function keys and touch screens. Most interfaces incorporate dedicated function keys — buttons with a specific name, number or symbol to identify them — which perform one specific function. The problem here is that dedicated function keys have their limitations: each option or function added to the control panel requires another key.

Does Miniaturization Really Matter?
Figure 3.
As a result, touch screens have become a popular method of operator input. Users can access large amounts of information with touch screens as they are guided through a series of choices with a simple touch of the screen. Interfaces incorporating touch screens tend to be smaller in scale and more user-friendly than those using dedicated function keys. However, touch screens also have drawbacks — users are frequently unsure if contact has been made with a touch screen, and users often inadvertently touch the screen where they did not intend to touch it.

The programmable switch combines the user feedback and clear actuation of a function key with the multiple functions and options of a touch screen. As a function key, the LCD or OLED switch can be programmed to perform many specific functions. Unlike a dedicated function key, a programmable switch can be labeled with and perform numerous options. Of course, the size of these switches can only be reduced so much before they become user-unfriendly because the programmable switch screens cannot be read, or because so much functionality had to be removed to accommodate the ultra-miniature size that they no longer offer the same enhanced ability which made them appealing in the first place.

Does Miniaturization Really Matter?
Figure 4.
equipment in order to measure angle movements above or below a horizontal axis. Until recently, tilt switches relied extensively on the use of mercury to measure angle changes. However, several mercury-limiting regulations have been implemented both in the United States and internationally. Changes to environmental manufacturing regulations — like the Environmental Protection Agency's (EPA) mercury ban and new global restrictions like those included in the Restriction of Hazardous Substances (RoHS) directive — have required a complete redesign of the tilt switch. With the advent of solid state tilt switches, industry designers have not only found a compliant device but a more sensitive, reliable switch than was previously available.

Solid state switches contain two solid state devices: an infrared light emitting diode (IRLED) and a phototransistor. They are angled slightly toward each other, creating a focus point. The switch also contains a bright nickel- or gold-plated steel ball that functions as the mirror, resting at the focus point when the tilt switch is level. In the level condition, the infrared beam is reflected by the mirrored, curved surface of the ball to the phototransistor to conduct. When the switch is tilted, the ball moves out of the focus point and the phototransistor is activated. These designs offer the smallest footprint for implementation of mercury-alternative devices and much greater safety enhancements, but they are often overlooked when all that is being sought out is the smallest conceivable switch available.

Environmental Considerations
Wireless devices, by their very nature, provide users with the freedom to move about and transition from one location to another without the inconvenience of having to switch from one hard-wired apparatus to another. However, the freedom of movement they provide can also be their Achilles heel if thought is not taken beyond simply trying to make them as small as possible. Consider for a moment some of the environmental hazards electronic devices face: moisture, corrosion and dust, to name just a few.

Incorporating a switch simply because of its small size into an interface that will be used in harsh environmental conditions can result in dramatically decreased switch life expectancy and even critical switch failure if it is not properly suited for those conditions. Furthermore, ultra-tiny switches often lack the ability to withstand extreme or even moderately severe conditions. Obviously, devices that will never see the light of day, a drop of water or even a fleck of dirt probably do not need extreme environmental barriers built into them, but designers should still think beyond switch size and consider all conceivable scenarios where the device may be exposed to adverse conditions that could result in premature switch failure and then plan accordingly.

The application of the device and what its switches will be used for is also an important issue to weigh against choosing a smaller switch for the sake of its size. In addition to determining if tactile feedback mechanisms, illumination, legends and easy field replacement or repair capabilities are necessary, engineers must consider frequency of use and reliability under extreme use circumstances.

Consider for a moment switches used on the many wireless medical devices used in hospitals. These switches are typically used with great frequency and in situations where a switch failure could be catastrophic. In this case, and in many others, close attention must be paid to switching cycles. In situations where a switch failure can be disastrous, a minimum switch cycle of 20,000 should be sought. The smaller a switch is, however, the more difficult it is to obtain such robust specifications.

These considerations for switch selection go beyond mere cosmetics. For nearly all switch applications, reliability, efficiency and functionality are just as important as size, if not more so. Wireless device engineers should look beyond the "smaller is better" ideology and consider the features offered by new switch technologies, the environmental rigors their devices may be required to face and the unique application demands that will push their devices to the breaking point.WDD