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NXP board turns audio jack into plug-and-play interface

Posted: 29 May 2014 ?? ?Print Version ?Bookmark and Share

Keywords:audio jack? 3.5mm jack? smartphone? plug-and-play?

NXP Semiconductors has unveiled a quick-jack solution that transforms a smartphone's audio jack into a self-powered data port. It adapts the standard 3.5mm jack to control external devices, as well as support application development.

The inspiration for this idea came from the University of Michigan's Project HiJack. The project harvests power and bandwidth from the mobile phone's audio interface for creating small phone-centric sensor peripherals that support plug-and-play operation.

NXP quick-jack

Figure 1: The OM13069 smartphone quick-jack platform repurposes the audio jack, making communication with external devices as easy as plugging in headphones.

Similar to HiJack, the NXP platform leverages the audio jack to provide power to the board for reading sensor data, which can then be stored, displayed, and quickly transmitted to the cloud. It aims to give designers a plug-and-go connectivity for adding features to applications including wearable medical and fitness devices, gaming controllers and toys, and diagnostics and maintenance tools.

The platform is compatible with iOS and Android devices. It runs with an application, 'NXP Quick-Jack', which can be downloaded for free from app stores. 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.

In conjunction with the launch, NXP will host a competition to encourage application development with the quick-jack board. Designers have to write a short description of their design idea. The contest is now open and entries will be accepted until June 20, 2014.

32bit building block

The platform is based on the company's LPC812 MCU. The low-power, 32bit device processes all the hardware interfacing and software protocol handling, enabling the board to communicate with the smartphone.

To facilitate the communication, Manchester coding is implemented. Transitions at the start of a period are overhead and don't signify data. They exist only to place the signal in the correct state to allow the mid-bit transition. The existence of guaranteed transitions allows the signal to be self-clocking, and also allows the receiver to align correctly. The encoded/decoded data is exchanged over the audio channels.

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