Integrated Loudspeaker Communication and Voice Broadcasting System for Riverboats

Customer

Kurs Central Research Institute, the leading research institute in the shipbuilding industry.

Objective

Development of a digital loudspeaker communication and voice broadcasting system for riverboats and vessels.

Platform design requirements

The system should be based on modern technologies for transmitting digital information. It should integrate a range of services and provide all kinds of two-way intercommunication: with the bridge audio communication between the control unit (CU) and the subscriber unit (SU) with data link control operation of each digital data link a backup power source and back when the primary power source is available

• Loudspeaker communication on board the ship
• Broadcasting circular warnings and programs
• Two-way communication

Solution

The developed system provides:

• Digital two-way
• Building a star-type network to ensure independent
• Automatic switching to
• Support for high-quality audio broadcast; the bit rate is 44 100 Hz, 16 bit

Basic technical parameters of the developed system:

• Support for up to 10 broadcast zones, four with feedback and six without feedback
• An independent galvanically isolated power supply from 24V direct current two sources, primary and backup
• An SU-integrated 20W audio amplifier designed to work in 100V audio lines
• RS-485, a wired digital data interface

Operating conditions:

• Operating temperature range: from -10 to +40ºÑ
• Storage temperature range: from -20 to +85ºÑ
• Relative humidity: from 95% at 25ºÑ, up to 80% at 40ºÑ

Concept

The system is based on the star topology in which each component communicates with the entire system through a wired communication interface. The system implements digital transmission of both operational data and audio data. developed software, both the CU and the SU were based on the STM32F103x, an inexpensive ARM Cortex-M3 microcontroller.

The system includes the following components:

• Control unit (CU) – installed on the bridge; it controls and monitors the entire system, as well as offers background music playback
• Line switch (LS) - the central communication hub, which provides two-way wired interface switching between the CU and the SU
• Subscriber unit (SU) - comes in two versions, with and without feedback. The feedback version uses a microphone

Circuit design

In order to standardize the developed software, both the CU and the SU were based on the STM32F103x, an inexpensive ARM Cortex-M3 microcontroller.

VS1053, a Vorbis OGG hardware codec, was used for encoding/decoding digital audio data.

An inexpensive and easily accessible XC3S200A-series FPGA by Xilinx was used for switching wired interfaces.

The SU and the line switch use the developed circuit of a galvanically isolated power source from two 24V direct current sources, main and backup. At the same time, the system implements automatic reserve / recovery switching in case of loss or appearance of the primary power supply.

A D-class 20W audio amplifier circuit was implemented inside the SU. The audio amplifier is designed to be used for 100V audio lines.

Structure

Large-scale 3D models of all system components were developed to arrange the elements inside the ready-made plastic enclosures and prepare documents for finalizing the details.

Software

The project involved the development of software in C for the CU and SU board microcontrollers, as well as an LS circuit in VHDL.

In order to standardize the developed software, FreeRTOS, a real-time operating system, was used between the CU and SU boards.

Drivers were developed for FreeRTOS to work with Ogg Vorbis, a hardware codec for streaming transmission of audio data.

Advantages

The developed loudspeaker communication and broadcast system has a number of advantages over analogous systems:

• Digital transmission of compressed high-quality audio data, Ogg Vorbis 44100 bit/sec, 16 bit
• Data link control for line breaks
• Modular structure
• A 20W integrated audio amplifier

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