Electric Vehicle Warning Sound System: Page 2 of 4

July 08, 2020 //By Andreas Pellkofer, Jagannath Rotti, Danny Ko, Analog Devices
Electric Vehicle Warning Sound System
Since electric vehicles do not emit the sound pedestrians and other traffic participants need to get alerted, the legislators all over the world stipulates that electric vehicles must be equipped with appropriate electronic noise generators. This article presents an elegant and easy to implement solution.

Figure 1 shows the different processing blocks inside the ADSP-BF706. External waveform audio files (WAVs) store signature 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.

Figure 1. Processing blocks on Blackfin+ processor

The ADSP-BF706 utilizes 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 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 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 band. The 3 V to 42 V input voltage range of the LT8602 makes the device ideal for automotive applications, which must regulate through cold crank and start stop scenarios with minimum input voltages as low as 3 V and load dump transients more than 40 V.

Figure 2. Detailed system block diagram with a Blackfin+ processor on a full featured board

Figure 3 shows an alternative system block diagram with connectors, a reduced set of peripherals, and one automotive qualified connector carrying all relevant signals. This configuration allows the design of a smaller form factor board.

This system solution results in a reduced system bill of materials (BOM) cost because the ADSP-BF706 acts as a microcontroller and an audio processor.

Figure 3. Detailed system block diagram with a Blackfin+ processor on a board with reduced components

For full details on the solution, see the EVWSS v1 Demo Manual and the EVWSS v2 Demo Manual, which are provided in the software download package. This software package (EVWSS-BF_SRC-Rel2.0.0) is available by request from the Software Request Form page on the Analog Devices website. For full details on the ADSP-BF706, see the ADSP-BF70x Blackfin+TM Processory Hardware Reference and the ADSP-BF7xx Blackfin+TM Processor Programming Reference.

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