Smartphone audio jack becomes a self-powered data port

June 02, 2014 // By Graham Prophet
NXP Semiconductors’ Smartphone Quick-Jack simplifies connecting a variety of external devices to smartphones for self-powered data communications. Adapting the standard 3.5mm audio jack found on smartphones, the Solution creates a universal interface for external sensors, switches, peripherals and other devices.

Inspired by the University of Michigan's Project HiJack, it gives mobile, consumer and industrial product designers simple, plug-and-go connectivity for adding features to a variety of applications, from wearable medical and fitness devices, gaming controllers, and toys, to diagnostics and maintenance tools.

Many app features depend on connectivity with external devices to collect readings from sensors, control switches, data collected by external meters, as well as act on user inputs from keyboard, wands, or joysticks and more. For these types of apps, tying up the phone's high-bandwidth USB/Lightning port is unnecessary. While wireless connectivity offers user convenience; it can also increase BOM cost in small devices and requires experience working with wireless protocols, and an external power source. By repurposing the audio jack, the Smartphone Quick-Jack solution makes communication with external devices as easy as plugging in headphones.

"We initially designed HiJack to create a universal way to connect low-cost sensor devices easily and securely to any brand of smartphone, tablet, or even PC," said Prabal Dutta, Assistant Professor, EECS , University of Michigan. "Today, the applications for audio jack connectivity have exploded, from our original vision of low-cost measurement instruments, to mobile entertainment, secure card readers, remote controls, personal medical monitors and many more."

For end-product designers, the Smartphone Quick-Jack Solution puts smartphone UI features at their fingertips for data display, controlling switches, monitoring sensors, collecting diagnostics and other field data. The phone's wireless connectivity supports data upload, storage, firmware updates, and general communication with the cloud, without the need to configure extra hardware or software.

For smartphone app developers, the solution provides plug-and-go data connectivity and power for external devices, making it simple to add sophisticated, user- or environment-aware inputs and features into smartphone apps. It also creates a secondary data/control channel for use when the USB/Lightning port is busy.

The Smartphone Quick-Jack Solution comprises a small board, a free example app for popular smartphone OSs, and design