Ultra-low power sound/audio sensor for LOUD noises

Question

I'm searching for a sound/audio sensor with ultra-low power consumption to detect the presence of a really loud noise (100dB+). The controller runs on battery and there is no option for a different power supply.

For me as a non-expert there seem to be two major types of sensors:

• Electret microphone (with potentiometer): Here I had a battery life of not more than a week. But the device works as intended due to the right sensitivity.

• MEMS microphone: These do look like the real power savers but the byproduct seems to be some way too high sensitivity. I read about that Vesper VM1010 (https://vespermems.com/products/vm1010/) which looks like a perfect fit (if the noise threshold can be set high enough) with about 10us current but as a hobbyist I'm totally unable to do anything with PCB and I can not find any (cheap!) breakout boards.

The common use case for sound sensor seems to be the detection of (very) low noises and I have been searching for a while now to find my product. And yes I even considered to design my own PCB circuit but I have a lack of electronic knowledge and I just don't want to believe that there isn't any smart solution for simple people.

I really appreciate any help or suggestion you can give. Thanks a lot!

Answer 1

Try using an ordinary loud speaker as a microphone. And it doesn't require any applied power.

The moving coil and magnet generate a voltage.

Loud speakers come in a variety of low impedances.

Answer 2

A piezo transducer might suffice to provide a voltage needing no amplifier. However, these are high-impedance devices, and to preserve the large output voltage, it must see a load resistance that is large.
As a test, a piezo element was measured with a 10Mohm oscilloscope. A "hand-clap" was the source of loud noise, about six inches away. When changed to a 1Mohm load, results were similar. It produced the following voltage, whose peak-to-peak maximum amplitude reached about six volts:
This particular piezo transducer was surrounded by a plastic shell, which provides a large resonant peak at about 3.4 kHz. That results in a sinusoidal wave that swings above and below zero volts. There are about seven cycles within each (dotted) division of the oscilloscope scale (0.002 seconds per division).
You could quite possibly hose this transducer up to a microcontroller's analog-to-digital converter directly - no amplifier needed. A few large-value bias resistors might be necessary to establish a known DC voltage at the input pin.

This might even work hosed up to a CMOS or HCMOS logic gate input.

Answer 3

The VesperMems product seems to be ideal for your requirements; amplitude detection, variable threshold and ultra-low standby power.

All you need is about 80 dB of attenuation, across the whole audio frequency which is harder than it sounds ( pun intended ) as lots of materials behave more like a low pass filter, so you can still hear the bass.

This may require some further research on your part to identify the spectral sensitivity of 100dB which to humans becomes an almost flat response. Courtesy WIki

When you use a speaker or microphone, you can imagine how loud it is when you tap the diaphragm. So protection from these near-field vibrations must be isolated or prevented.

Acoustic Pressure is logarithmic (dB SPL) meaning it spans many decades of power levels and choosing a calibrated 100dB can be done, but this is another task for you to define, as well as defining the minimum event duration and stretching the event to stay ON or to some interface device.

So there is more to your design specs than simply choosing the sensor.

Answer 4

For gunshot detection in a battery powered sensor, there are two critical parameters for the microphone: Acoustic Overload Point (AOP) and power consumption.

Standard analog MEMS microphone

There are many MEMS microphones with excellent performance in both areas. For example:

• ISC-40638. AOP 138 dB SPL, 170 µA
• IM73A135. AOP 128 dB SPL, 170/70 µA
• Vesper VM2020. AOP 152dB SPL, 248 µA

For level trigger one might need a rectifier and preamplifier, which would bring power consumption of 100-300 uA, depending on the chosen microphone.

MEMS microphones with built-in triggers

An alternative to a standard analog MEMS microphone, would be to use one that includes trigger.

The VM1010 mentioned in the post has the highest trigger point at 89 dB SPL.

There was also the VM3011 (now discontinued), which has the trigger level configurable over I2C instead of analog. The highest dB level it can trigger at is 91.5 dB SPL. Power consumption in idle is 10 uA. However, note that these soundlevels are measured in the area of 2-800 Hz. So one needs to check if that fits the intended application.

If a trigger point higher than this is needed, one could consider acoustic dampening to achieve that. For very loud noises, like explosions and gunshots, one may also want that to protect the microphone.

For a complete sensor, one may also need a microcontroller, as well as a data transmission system. The power budget for data transmission would depend a lot on the range needed, choice of networking technology.