The use of the basic mobile device has expanded tremendously with the rapid adoption of user-selectable software applications, or apps. And as these new and innovative apps have grown, so has the need for user-purchased hardware adapters to enable them. For example, credit card readers can be directly connected to a handset’s form factor to allow users to swipe a credit card, turning the handset into a point of sale device.

In the 1990s, only a fraction of the population owned mobile phones, which were used purely to make phone calls, similar to landline units. The differentiation from phone to phone focused on the tangible quality from manufacturer to manufacturer. Common differentiating factors included size (the most common phone initially was the “bag phone”), battery life, and form factor (flip, slider, etc.).

As technology evolved with component integration, it became evident that there was room to add more components to a handset and enable increased software and hardware functionality for even greater market differentiation. Now, the mobile phone is a wireless minicomputer in a very small form factor. A typical smart phone today has more than 11 million lines of code to support the network connection and user interface (Fig. 1).

The Origin And Expansion Of The App

Hardware became more readily available in the handset, and memory in particular was a simple novelty that engineers initially enabled to utilize simple software scripts to permit the user to “doodle” or play time-consuming games. These free programs were included in the handset operating system, yet these simple software scripts could be expanded to more entertaining and eventually useful tasks. Thus, the app as we know it was born.

Most apps now are software-centric and utilize existing hardware within the handset. These apps are marketed to function like much larger well-known devices. As an example, metal detector apps can be downloaded for a small fee to achieve limited functionality. Apps can be found in ever-expanding categories and are available to operate over different handset application environments.

At a recent conference of service providers, it was announced that the release of apps has accelerated to more than 25,000 per month available to the public! The biggest challenge in increased app functionality is having the additional hardware to enable the software application. Fortunately, certain I/O interface standards have been adopted within handsets that allow a hardware expansion to the mobile device. The most common standard is the Universal Serial Bus (USB) port.

USB Provides Expanded Functionality

The USB port on a handset has evolved as a universal interface. Many USB ports utilize the Micro-USB connector as a mechanical interface, which is predominantly standard, and then also utilize a standard set of D+ and D– data interfaces and a somewhat standard power interface. The USB interface typically routes power to the handset (for charging).

However, some manufacturers allow the handset to source small levels of current. Fortunately, the power and ground pins are in a standard location. Finally, an ID pin on the connector may be utilized for accessory detection. Again, each manufacturer has its own standards for such pin utilization.

Because the mobile device USB port can supply power and a data protocol, the app developer can now expand to the “outside world” of the handset and develop applications that may utilize hardware and sensors not designed into the handset. The primary challenge is to develop the mechanical hardware interface to the mobile device as well as the hardware switching to enable the new functionality without destroying the original hardware configuration.

Connectivity Solutions for Expanded Applications

Credit card reader adapters may be connected to the mobile phone via USB. To retain the same functionality of the USB port and allow use of the new application, regulating and switching components are both required within the credit card adapter. USB is not a multi-drop architecture, so it must be switched to the appropriate point (Fig. 2).

The switch is required for the USB path to retain the signal integrity necessary to support HI Speed USB and to minimize electromagnetic interference (EMI) from unused USB stubs. The switch for the ID detect is required to allow continued use of the ID detect feature if the credit card reader adapter remains connected to the handset. The buck power supply reduces the 5 V from VBUS down to the 3.3 V required for the ASIC controller, yet passes VBUS to the connector.

Mobile Handsets As Diagnostic Devices

Because of their computing and interfacing power, handsets may be expanded to certain medical diagnostic applications. For instance, the handset could serve as the primary application software host for a blood pressure monitor interfacing through the USB port. Of course, the device may be limited to U.S. Food and Drug Administration (FDA) regulation (Fig. 3).

The mobile handset has only just begun its transformation from basic telephone functionality to that of a microcomputer controlling a vast array of expansion devices. These devices require standard interfacing techniques such as USB, but they also need additional hardware to retain the original functionality as well as adapt and enable the new application.

Handsets can do more than serve as health monitors, acting as platforms for a variety of functions. For example, they can be automatic, secure financial transaction points. They can even configure personal seat, radio, and environmental settings in automobiles. With the right interface, the possibilities are endless.