Data transmission through Audio Jack

on iOSShipeng Xu 25-08-2014

github.com/billhsu billhsu.x@gmail.com

Problem

Not available on Android

Not available on iOS Expensive

Solution - Audio Jack!

picture from: http://support.creative.com/kb/ShowArticle.aspx?sid=111079

Apple:Left Audio, Right Audio, Ground, Mic Most Android devices: Left Audio, Right Audio, Mic, Ground

Contents• jackDuino overview

• How to harvest energy from audio signals

• How to transmit data through audio jack

• Applications for audio jack-based gadgets

• Case study: Thermometer

• Case study: Credit Card Reader for Mobile Phones

Intro to jackDuino• http://github.com/tikoLabs/jackDuino

• Designed when in university

• Inspired by

• SoftModem

• “Hijacking Power and Bandwidth from the Mobile Phone’s Audio Interface”, University of Michigan

jackDuinoATTiny8 MCU

(Arduino compatible)

MiniUSB port

(For programm

ing)

Audio plug

GPI

O

Transformer (Harvesting energy)

Harvesting energy from audio signals

- Send a square wave signal from right audio channel - Maximum power from audio jack:15.8 mW - 47% power transfer efficiency(7.4mW)

- enough to power a MCU and several sensors - from “Hijacking Power and Bandwidth from the Mobile Phone’s Audio Interface”, University of Michigan

TransformerAC bridge

Demo for energy harvesting

Communicating with iPhone - Frequency-shift keying

• FSK(Frequency-shift keying)

• 4900 Hz -> 0

• 7350 Hz ->1

• BAUD RATE: 1225(153.125Bytes/Sec)

• Manchester Encoding(Better way)

Communicating with iPhone - demodulator

Communicating with iPhone - demodulator

Time difference

Noise cancelation

Update counters

Applications for audio jack-based gadgets

Case Study: Thermometer

*Thanks Laurence and HackerSpaceSG for the components :-)

Thermistor

Case Study: Thermometer - Circuit

Case Study: Thermometer - App Design

• Subh

Case Study: Thermometer - Demo

Case Study: Credit Card Reader for Mobile Phones

Case Study: Credit Card Reader for Mobile Phones

Case Study: Credit Card Reader for Mobile Phones

CoilResistor (protect the mic input)

Back Front

Case Study: Credit Card Reader for Mobile Phones

http://proteanecho.files.wordpress.com/2012/06/card-read1.png

Case Study: Credit Card Reader for Mobile Phones

• Data on credit card is not encrypted

• Malicious apps might listen on phone’s mic

• Use jackDuino for encryption

jackDuino

Case Study: Credit Card Reader for Mobile Phones with encryption

Coil ADC Encrypt iPhone

Thanks