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Audiophonic alarm pocket receiver for deaf person : technical and ergonmic choices

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et P. MORGAND (THOMSON SINTRA Activités Sous-Marines)

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Proceedings of ECART 3 "European Conference on the Advancement of Rehabilitation Technology", Lisbonne


The aim of this paper is to give an overview of AUDIALARM : an audiophonic alarm pocket receiver for deaf person. At first, the system is described and its technical features are given. Then the ergonomical approach is introduced : one of its main characteristics is that it relied on working teams with endusers. Finally the implementation architecture is presented.


This project is included in a Thomson-CSF program, a french Defense Company which wants to exploit R&D technics that are commonly used for Defense activities in order to develop some technical help systems for Disabled people.

This daily support equipment is dedicated to deaf persons, or persons who are hard of hearing. It is based on underwater acoustics technics using automatic analysis and identification of sound (signal analysis and classification). This type of technics gives a low rate of false alarm and the sound identification efficiency is generally better than 95 %.

Audialarm is especially designed to facilitate the professional insertion of deaf person in offices or factories. In such environments a technical help is needed to alert the person that an emergency alarm or a communication warning is emitted.

1. Systems description

This system is composed of two equipments that are a pocket case and a vibrative wristwatch.

On the one hand, this case is to be worn in a pocket or with a shoulder strap by a deaf person using it in the street or public tranportation.

On the other hand, Audialarm might be disposed on a desk or a piece of furniture in office or at home. The main function of the pocket case is the acoustic signal detection and automatic identification of eight different alarms or warning such as : Fire alarm, phone (french Minitel for deaf person), Police or firecar alarm, klaxon, intercom signal, subway door shutting, ... The automatic identification is realized in three main steps as following :

  • pre-warning issued by a SSI working on the acoustical signal detected by a waterproof microphone,

  • data acquisition and first signal analysis based on specifics signal characteristics in time and frequency. This first analysis needs a time processing of 1.2 sec. ;

  • in a third step, for complete identification, a finest signal analysis is used if the first analysis classifies the raw signal as a sound among the eight alarms or warnings. This stage needs a processing time of 1.7 sec.

The kind of the alarm or warning is clearly displayed on the pocket case (alphanumericaly) three sec. later the sound detection in ambient noise. At the same time a VHF signal is sent to a vibrative wristwatch. The range of the radio transmission between transmitter and receiver could reach 50 meters in free field.

This wristwatch that includes a VHF receiver will vibrate in order to inform the deaf person about an alarm sound generation in the vicinity of the case. Each type of warning (Home ring, alarm street, fire alarm office...) is codified by one, two, three or four vibrations. A clip belt (working as before) could also be used instead of the wristwatch.

This autonomous equipment composed of a pocket case and a wristwatch (or a clip belt) can be used at the office, in the street, in public transportation and at home without any modification of local infrastructure.

2. Ergonomical approach

The aim of the ergonomical study was, for the engineers that designed AUDIALARM, to check that the system would fit the needs of future users.

An ergonomical process has been carried out at the beginning of the system specifications studies along with the realization of a feasibility demonstrator dedicated to the robustness tests of the signal processing algorithms. A prototype has been realized with a portable computer fitted with a real time processor board.

Some specifications constraints were already given at the begining of the designing phase, such as :

  • the choice of a vibrative wristwatch,

  • the list of the eight sounds to be identified.
These specifications were included in the contract accepted and supported by the AGEFIPH (see [[section]].5). The ergonomical approach was realized as following :
  • System functionnal analysis and comparison with other products for deaf persons.

  • Meetings with hospital professor, doctors, specialists in artificial hearing systems, associations for deaf people, social workers,... in order to get familiar with the concerned population.

  • Creation of working groups with a sample of future endusers (25 people).

  • Synthesis of these investigations and modification of the initial system specification.
In the next phase of the project, one prototype will be tested by the members of the user team in order to take into account the endusers advice.

3. Architecture and technology

The pocket case is designed with a processing life of eight hours (without battery recharge) and for one hundred identification sounds. Recharging could be easily done at home or office during the functionning of Audialarm.

Audialarm is based on a High Technology system using an audiophonic conversion in 16 bits, a SSI detector and a 32 bits signal processor as a TMS 320C30.

All the software and identification keys are supported by a PROM. This component would be easily replaced and the pocket case could operate on other kinds of sounds. The dimensions of the pocket case ( 5x3x1 inches) have requested some electronics integration efforts. CMS technics have been used for the development of this equipment.

4. Acknowledgments

This work was done in cooperation with the BUCODES, french association for people that turned deaf, and supported by the AGEFIPH (french organization for professional insertion of disabled people).

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