Headphone jack turns into peripheral port
NXP has put together a reference design for attaching external sensors and switches to phones via the headphone jack – inspired by the University of Michigan’s Project HiJack.
The idea is that many apps can operate though a low bit-rate interface and do not need to tie-up the phone’s fast USB or Lightning interface – keyboards are an example.
“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,” said NXP.
“We initially designed HiJack to create a universal way to connect low-cost sensor devices to any brand of smartphone, tablet, or even PC,” said University of Michigan researcher Prabal Dutta.
The board has:
LPC812 microcontroller to handle decoding/encoding of the Manchester algorithm (left audio channel has the data) and communication with external peripherals.
A standard header for connection of sensors, switches, or data-collection devices.
A power circuit which draws power from the right audio channel to feed the board and attached components.
A miniature joystick, which controls the example app.
Source code for the LPC812 is free, and ready to use with NXP LPCXpresso tools.
There is an application competition.