Hardware structure of tangible acoustic interface systems

C. Bornand^a, A. Guichard^a, M. Yang^b, Z. Wang^b, Z. Ji^b, M. Al-Kutubi^b

^aUniversity of Applied Sciences, Switzerland

^bCardiff University, UK

Tai-Chi, a European Project (FP6)

Goals:

• To develop new types of interaction between humans and computers.
• To create new interaction media: walls, tables, 3D objects, …
• Physical porperties exploited: acoustic waves propagation in a solid or in the air.

 

Priciple of Tangible Acoustic Interfaces

Any physical contact with a surface will change its acoustic behaviour:

• Two different detection ways have been used
• passive method
• active method

 

 

Principles (con.)

• TDOA – Time Delay Of Arrival
• Acoustic holography
• Time reversal
• Visual analysis

Specific goals:

• Unique impact detection
• Multiple simultanous impacts detection
• Drawing detection

A proposed prototype: based on Time Difference Of Arrival

To obtain the localisation of the impact:

• Time of flight estimation between the impact and the sensor.

• Impact localisation: we know the velocity of the acoustic wave on the surface, Then hyperbolic intersection gives the impact localisation.

Precision: 3 cm.

Difficulty: to determine the time of arrival

Diagram of TDOA

  

An application example

  

Requirements for developping a TAI

• Acoustic waves sensors
• Simultaneous acquisition of signals
• Intense signal processing
• Results transfer:  needs of synchronisation
• Results exploitation

System hardware structure

 

Embedded DSP system: PRESTO

 

Sensors

Piezoelectric device were selected

• PVDF piezoelectric film
• Ceramic piezoelectric sensor
• accelerometer
• sounders

Packaging methods were studied

Sensor structure

Signal conditioning circuit

 FPGA based controller for data acquisition

 

 

 

DSP system: PRESTO

• acquisition board
• processing board
• communication board

 

 

Software on PRESTO

2 versions

• Acquisition only all processing done on PC
• Acquisition and processing PC used to exploit the results of localisation

Data exploitation on PC: realised with EyesWeb (www.eyesweb.org)

 

 

Features of TAI-CHI prototype

• open hardware architecture for single-processor or dual-processor applications using I/Os and communication
• TAI library (Tangible Acoustics Interface Algorithms)
• floating point processing or fixed point processing both available
• synchronization mechanisms to realize isochronous operations and transfers as necessary for multimodal applications
• Ethernet, Firewire, RS485, …
• compact dimensions to enable its integration into prototypes or small series
• reliable interconnection system
• industrial temperature range (-40…+85oC)

Conclusion

TAI-CHI prototype will give birth to a product:

• TAI-CHI development kit
• Available: autumn 2005
• The TAI-CHI development kit will enable faster market access to TAI application