EYE on NPI: ST Micro’s AIS25BA 3-Axis Accelerometer #EYEonNPI #DigiKey @DigiKey @st_world @Adafruit
This week’s EYE ON NPI (video) has great vibes, it’s ST Micro’s AIS25BA 3-Axis Accelerometer, a unique take on the classic tripe-axis motion sensor where data is streamed out with a TDM interface rather than I2C or SPI!
We’ve never seen this kind of sensor but the idea behind its use case is kinda cool and is a great demonstration of using sensor fusion to cancel out or extract data from two ‘directions’.
Usually accelerometers we’ve covered on NPI before are used for tilt or motion sensing, detecting if something is falling or was struck. Another good use for this common sensor is vibration detection. You need very fast sensor reading but any vibration can be detected and sensed as motion and then integrated for displacement. That’s pretty much what a microphone does as well, right? It takes vibrations in the air, then the displacement is converted to a capacitive measurement via MEMS or current/voltage measurement via electret.
So, what if in addition to measuring the air movement with the microphone, we also got to measure the vibration of a surface with an accelerometer? Dense surfaces will be better at low frequency measurements, and the microphone element will be better at high frequency. With a little filter work, we can combine these two data streams so that we get clear audio without the motion or air noise that often adds crackling, or overwhelms the analog front end.
ST Micro’s AIS25BA 3-Axis Accelerometer is the automotive-qualified version of the LIS25BA but both function basically the same so choose whichever is best for your application. In both sensors, the configuration and test is still done over I2C – setting gains, offset, self-test, etc. Then data is streamed over a TDM audio-interface so it can be quickly funneled into a DSP or microcomputer that performs the high/low-pass filtering and merging. As demo’d by an ST engineer, the sound quality is greatly improved, kinda like a reverse-noise-cancelling-headphone.
Particularly as so many more devices like cars are becoming voice-controlled to allow for advanced uses, and avoid mechanical components that can wear out or get dirty, having good clean audio input is key to having a user experience (UX) that is great versus one that is annoying to use. There’s even a driver for the I2C side of things over on GitHub to get you started quickly.
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