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Basic Considerations for Mobile Device Design

Mobile devices – devices that are easily transported and typically are handheld and powered by a battery – have unique challenges in their design to enable usability, ruggedness, and reliability. Characterized by relatively lightweight and small screen size, they span a wide range of device types and applications, including mobile phones and tablets. Mobile devices also include custom devices designed for specific use cases, such as military, medical, or industrial applications where particular peripherals, security, certification, or regulatory requirements must be fulfilled.

Users of mobile devices require a number of characteristics: portability, ease of use, advanced and diverse capabilities, and durability. The application may require the integration of specific sensors, connectors, communications ports, and more, compliance with a number of industry or government mandated standards, and perhaps long term availability. A successfully designed mobile device is a simultaneous solution of a broad array of competing requirements along with engineering and business constraints. At a high level, design considerations include the following:

Small screen size that fulfills many needs: While mobile device screen sizes must be relatively small, it’s imperative that the screen be effective and dynamic. The display must be sharp to adequately render small font sizes and high resolution images or graphic content. Vibrant colors help convey information. To avoid ambient light reflections in brightly lit environments, especially sunlit, and to strengthen displays from frontal impacts, any cover glass or touchscreen overlays should be optically bonded to the LCD and use a form of chemically strengthened glass.

Straightforward commonsense user interface: Small screens constrain the flexibility of user input and potentially menu driven navigation. The design of the mobile device must ensure that usage is both rational and user-friendly. In addition to clear on-screen text, icons, and graphical content, the implementation of buttons or switches for critical or common device operations may promote usability. The device style and design should be effective and attractive without confusing or overwhelming the user.

Use cases: Specific use cases lead to implementable sets of requirements for the mobile device. These include battery life, user interaction, communications (such as need for cellular, Wi-Fi, or Bluetooth radios), storage, sensors, and more. This leads to selection of a microprocessor, operating system, amounts of memory, and the peripherals integrated. Mobile device operating systems today often utilize Android or Linux; sometimes a real time operating system (RTOS) such as VxWorks is used where real time sensing or control is paramount.

Day-to-day reliability: Since users take their mobile devices with them, they must be durable enough to meet the strains of transportation, occasional unintentional drops, dust, rain, wide temperature swings, and more. Specific environmental use cases, with objectively testable pass criteria (often set by industry standards), impact the portable device design. There is a cost associated with enhanced ruggedness and reliability, which may be required to ensure device longevity.

Security: Mobile devices, with limited physical control while in the field and with vulnerabilities inherent in the communication mechanisms they use, must account for security. Hardware-level tamper detection mechanisms can sense an enclosure being opened and react by disabling device operation or erasing encryption keys, thereby keeping critical data safe. Built in software security can authenticate users or applications. Security is no longer an afterthought, but a necessary feature built into the initial design of the mobile device.

There are many considerations in the design and implementation of a custom mobile device. Use cases, regulatory and industry specifications, security, and business needs directly impact the hardware, software, and mechanical design. Successful custom mobile device design requires detailed planning, complete specification, and realistic expectations of the engineering effort.

SECO USA specializes in the customized design and manufacture of custom electronic devices for Original Equipment Manufacturers that have unique product requirements. In addition to embedded circuit boards, SECO USA specializes in custom-designed rugged tablets and portable handheld devices. Contact SECO USA for an evaluation of your application.

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