Low-Speed Warning System | EV Safety Solution WT2003HX-16S

I. Application Scenarios of Low-Speed Warning System in EVs

The Low-Speed Warning System is a critical safety feature for electric vehicles, ensuring pedestrian awareness and compliance with GB/T 37153-2018.

The new energy vehicle industry, as a key development sector in many countries worldwide, has broad prospects. Alongside it, various alarm system solutions are also flourishing. Among them, the low-speed warning system (AVAS) serves as a critical safety component, and its performance and reliability have a direct impact on vehicle safety. Our current solution, developed based on the WT2003H, provides sound prompts at speeds below 20 km/h, such as alerts for pedestrian approach, starting, and reversing. For details, please refer to the document “Acoustic Vehicle Alerting System for Electric Vehicles” (GB/T 37153-2018).

II. Functional Modules of Low-Speed Warning System

2.1 Existing Solutions + Planned Solutions

2.1.1 Voice Chip Control Block Diagram

Solution 1 (Existing): MCU controls the voice chip to provide speed sound effects, engine sound, etc. It supports reserved interfaces and onboard updating of the voice IC program and audio.

Control mode: single-wire communication. The update interface for the voice IC program and audio is UART (using our company’s downloader for onboard updating). Our latest version supports MCU updating of the entire voice bin file (including audio and program). For example, if there are 10 audio tracks and only one is changed, a new bin file can be generated for updating. Our voice IC will automatically check and skip duplicate data, updating only the different parts to achieve fast updates.

 2.1.2 Our Demo Brief

Main composition description:

Schematic diagram section:

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2.1.3 Brief on National Standard Testing of Low-Speed Acoustic Signals for Electric Vehicles

• Operating speed range: The operating speed range of the alert system must at least include greater than 0 km/h and less than or equal to 20 km/h. When the vehicle is stationary but in a drivable mode, the manufacturer may choose whether the low-speed alert system emits sound.
• Testing requirements: For the voice IC, the main test items are sound pressure (dB) and frequency shift (the change in acoustic frequency as vehicle speed changes). A sound level meter is used for whole-vehicle testing. For early product debugging, decibel meters and related equipment can be used for preliminary measurements.

Sound pressure limit test:

For automotive playback, an external amplifier is usually connected. During low-speed alarm playback tests, if the dB value is insufficient, the following ideas are applied:

• Ensure the voice IC volume is at maximum.
• Adjust the audio amplitude to ensure playback is distortion-free.
• If maximum amplitude is still insufficient, adjust the amplifier gain (feedback resistor value). Playback must remain distortion-free, and output power must not exceed the rated amplifier power. For example, with a 5V supply and 4Ω load, an amplifier can only drive a 2W speaker. If amplifier gain and input amplitude are increased, testing under load may push amplifier output to 2.5–3W, which risks damaging the amplifier and speaker.

Frequency shift test:

When the vehicle travels at speeds between 5 km/h and 20 km/h, the alert system must produce at least one 1/3 octave band frequency (specified in Table 1) that increases with speed or decreases as speed decreases. The minimum average frequency shift speed should meet ≥0.8%/(km/h). In practice, we set a 1% frequency change, with parameters adjusted every 1 km or 5 km to achieve the frequency variation effect.

Note: The above references are from the document GB/T 37153-2018.

Speed-frequency relationship reference: for every 1 km/h increase, playback frequency increases by at least 1% over the previous step (e.g., if 0 km/h = 1000 Hz).

Solution 2 (Serial Port Update Supported): MCU controls the voice chip for speed effects and engine sound, while the MCU updates voice IC audio files via serial port.

App delivers MP3 audio, with supporting MCU + wireless module / 4G module / BLE + app development.

Solution 3 (Planned): MCU controls the voice chip for speed effects and engine sound, while the voice IC directly connects to a Wi-Fi module (possibly Bluetooth or 4G in the future). Waytronic provides the app and webpage for audio synthesis or offers API interfaces for clients to develop their own upper-level applications.

1. In this solution, the MCU only needs to control the voice IC via UART playback. The wireless module (Wi-Fi, Bluetooth, 4G, etc.) interfaces with the voice chip to complete audio updates.

Audio files are synthesized via our upper-level webpage and deployed to the server. The app handles network configuration and file distribution. We also provide protocol information for communication between the voice chip and Wi-Fi module. The MCU issues command requests to the voice IC, which then applies for updates. Playback and update downloading share one protocol format.

2.2 Solution Comparison

• Solution 1: Traditional low-speed alarm solution. MCU + voice IC + amplifier. Voice IC controlled via our single-wire communication. Supports onboard updating. Suitable for production side.
• Solution 2: An upgraded version of Solution 1. MCU + voice IC + amplifier. Adds the possibility of updating via app with new Wi-Fi or Bluetooth module. Voice IC is changed to UART communication + MP3 update support (serial MP3 updates supported, frequency shift pending migration). Alternatively, use the latest Solution 1 version where MCU updates the bin file. Suitable for production, distributor/agent side, and terminal users.
• Solution 3: Waytronic provides a complete solution with server + app + wireless module (Wi-Fi, Bluetooth, etc.). Already in planning stage for full set: server + app + Wi-Fi module. Compared with Solutions 1 and 2, this wireless update method saves client development time, avoids new R&D costs, reduces MCU resource use, and shortens development cycle. MCU only interfaces with the voice chip. One unified protocol is used (unless the client wishes to develop their own Wi-Fi module, for which we also provide reference cases and API). Suitable for production, distributor/agent side, and terminal users.

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