MPUs and MCUs
Electric vehicle warning sound system
Blackfin-Based Solution
By Andreas Pellkofer, applications engineer, Jagannath Rotti, software lead, and Danny Ko, applications engineer, ADI
Introduction
Traditional combustion engine vehicles emit engine sound, even at low travel speeds. Typically, pedestrians and other traffic participants recognize an approaching or departing vehicle through sight and auditory identification of tire sounds and other emitted noise when the vehicle is out of sight. Electric vehicles (EVs) do not emit engine sound. Hybrid electric vehicles (HEVs) or plug-in hybrid electric vehicles (PHEVs) move almost silently when traveling at low speeds and before the conventional internal combustion engine (ICE) kicks in. These vehicles are difficult to hear when travelling at speeds less than 19 mph. At greater speeds, tire sound becomes dominant.
An electric vehicle warning sound system (EVWSS) produces a series of sounds designed to alert pedestrians to the presence of EVs, HEVs, and PHEVs. The driver can initiate warning sounds (similar to the sound from a car horn, but less urgent); however, the sounds must automatically be enabled at low speeds. These sounds vary from artificial tones to realistic sounds that mimic engine noise and tires moving over gravel.
Analog Devices offers two different solutions for advanced applications with an in-cabin engine sound for an EV as well as an external engine sound. Analog Devices developed a solution based on the ADSP- BF706. For entry-level systems, Analog
The ADSP-BF706 Blackfin+ processor provides a single-chip solution for audio processing and interfacing to the control area network (CAN) bus. Analog Devices developed a CAN software stack that runs on the ADSP-BF706, which enables users to build automotive grade demonstrations with minimal effort (a Vector CAN stack can also be used). Additionally, Analog Devices provides full hardware and software reference design and SigmaStudio compatibility for live tuning of parameters. Figure 1 shows the different processing blocks inside the ADSP-BF706. External waveform audio files (WAVs) store signature
16× pitch shifting, a recommendation from the United States NHTSA, which increases the frequency of the output sound as the vehicle speed increases. The ADSP-BF706 can dynamically control the volume as the vehicle speed from the CAN bus increases.
Figure 2. Detailed system block diagram with a Blackfin+ processor on a full featured board.
Figure 1. Processing blocks on Blackfin+ processor
Global governing bodies are exploring legislation that seeks to establish a minimum level of sound for PHEVs and HEVs when operating in electric mode so that visually impaired people, pedestrians, and cyclists can hear these vehicles approach and determine from which direction these vehicles are approaching. An example of this legislation can be found on the National Highway Traffic Safety Administration (NHTSA) website.
30 April 2021
Devices developed a solution based on the ADAU1450 SigmaDSP. These solutions can synthesize sound and adjust frequency, sound volume, and other parameters depending on the traveling speed, and these solutions can send the audio to an audio power amplifier. Depending on the requirements of certain legislation, the warning sound can be simulated using combustion engine sounds or any other synthesized tones.
Components in Electronics
engine sounds or audio tones. Up to 25 WAV files can be accessed simultaneously from the external serial peripheral interface (SPI). These files are frequency shifted and mixed internally in the digital signal processor (DSP) before adding the dynamic volume control. The ADSP-BF706 utilises a memory mapped SPI interface that provides faster, simplified access to the external memory, which eliminates the need for an external double data rate (DDR) memory for this application. Up to 25 WAV files can be accessed simultaneously from the SPI flash memory. The large number of accessible WAV files helps to create more realistic engine sounds. The ADSP-BF706
can also implement up to
Figure 2 shows a detailed system block diagram. A Power by Linear LT8602 quad monolithic synchronous, step-down regulator provides all voltage rails required in the system, derived from the 12 V car battery supply. The 2 MHz switching frequency allows users to avoid critical, noise sensitive frequency bands—for example, the AM
Figure 3. Detailed system block diagram with a Blackfin+ processor on a board with reduced components
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