Data transmission through Audio Jack
on iOSShipeng Xu 25-08-2014
github.com/billhsu [email protected]
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