The PionEar sensor concept is based on Syntiant TinyML board.  TinyML board is the ideal platform for building low-power voice, acoustic event detection (AED) and sensor ML applications. Equipped with the ultra-low-power Syntiant® NDP101 Neural Decision Processor, the TinyML board packs native neural network computation for the most demanding applications in the lowest power envelope.

The onboard microphone and BMI160 sensor enable easy configuration for any speech, AED or 6-axis motion-and vibration-related application. Trained models can be easily downloaded on the TinyML board through a micro USB connection without the need for any specialized hardware.

The below picture shows how the TinyML board is interfaced with other external circuitry. The external custom-designed PCB contains RGB LED for logo illumination, DC to DC power supply, and a phototransistor acting as a light sensor. The light sensor provides a signal (AIN) that is sensed by the TinyML board, which controls the brightness of the logo. This prevents the driver from being dazzled at night but enables good visibility in the daylight.

The li-Pol battery cell (800mAh) is connected directly to the TinyML board battery connector. It directly charges the battery when connected to a power supply via a micro USB connector. The whole system draws about 12mA while sensing and processing the sound signal so the battery can last about 3 days. I plan to significantly prolong battery life by leveraging integrated (or external) accelerometer. This will be sensing if a car is moving – if not, it will put the TinyML board into the deep sleep state where current consumption is negligible. The sensor will then operate only when car is driven.

In order to avoid charging the sensor at all, I plan to use a small solar panel and integrated module with MPPT functionality. I suppose there is plenty of time during a normal day when the sensor can be recharged unless the user is parking in the garage. The goal is to provide a device you do not need to care about at all.

Fig. 1) PionEar sensor HW block diagram

In order to deploy the machine learning model into a TinyML board the Edge Impulse platform can be preferably used. Edge Impulse provides easy to understand interface where you can create and manage your datasets, extract features, train ML models, test and finally deploy into numerous of supported hardware platforms. The TinyML board is fully supported so I have leveraged this advantage.

First, it is necessary to have a suitable dataset of emergency siren sounds and other road noises. One can find many public datasets – I have used Large-scale audio dataset for emergency vehicle sirens and road noises as a basis for my ML model. I have used other datasets of noises and speech to mix with the original dataset. My dataset including ML model is publicly available on the Edge Impulse platform – you can find it here. I expect, that I will further evolve it as I will continue with the prototype testing.

I consider the current version of the ML model sufficient for testing in real conditions. It can safely detect ambulance sirens and exhibits a low amount of false positives when exposed to road noises while driving. There are still some weak points for example music when listening to the radio in car. However, music was not part of the dataset because I expect that hearing-impaired people typically do not listen to the radio in a car 😊

Fig. 2) ML model accuracy for testing dataset