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Audio jack transforms into self-powered smartphone data port

29 May 2014

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An LPC812 MCU is programmed to transmit and receive data to/from the phone using the audio jack. Transmission uses the familiar Manchester Coding format to ensure convenient, reliable operation. The MCU automatically identifies microphone (MIC) and ground (GND) for quick and easy operation. The energy-harvesting block uses the right channel of the audio jack to output a 21.3kHz sine waveform. The block rectifies the signal and generates a DC output. The Quick-Jack board can also use a button battery for power when the phone isn't available.

Smartphone Quick-Jack solution block diagram

For end-product designers, the Quick-Jack solution puts appealing 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 Quick-Jack solution comprises a small board, a free example app for popular smartphone OSs, and design documentation. The board houses:

  • The LPC812 microcontroller to handle decoding/encoding of the Manchester algorithm (enabling use of the left audio channel for data transport) and communication with external peripherals
  • The source code for the LPC812, which is available for free and is ready to use with NXP LPCXpresso tools.
  • A standard extension header for easy connection of sensors, switches, HMI peripherals, or data-collection devices
  • An energy harvesting circuit that draws power from the smartphone over the right audio channel to power the board and attached components
  • An on-board miniature joystick to visualise data/signals and control the smartphone UI in the example application

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