[MiracleRabbit]

If these Shahed drones have a propeller they should have a brutal signature between 0-250Hz as they are moving a lot of air. And if the engine speed of the Shahed stays constant it will be even easier to detect it ("Angry lawnmower sound".. but that's only the high frequency part of it).

There are extremely sensitive differential pressure sensors (like SDP600-25Pa) available from Sensirion that aren't overly expensive.

Use one differential side and connect it to a kitchen funnel for directional listening the other one to a plastic bottle with a tiny hole in it. This way the sensor will "Null" out the environmental pressure (which the bottle follows very very slowly) from both inputs. It then only will pick up everything high frequency which is left over (and the bottle cannot follow because of its small hole).

This way I was able to detect washing machines that have a physical link to a house from many hundred meters (machine spinning -> house wall shaking -> pressure waves) away. The speed pattern of washing machines when spinning is very unique (several steps over many seconds).

Add this with some GPS PPS frame timestamping and you should have a nice tracking network that doesn't require a lot of bandwidth. But maybe the setup must switch to analog differential pressure sensors as these Senirion-I2C sensors do not have a Sync ping for super precise timestamping.

[Hnrobert42]

Interesting! There are a lot of super loud cars in my urban area. I want to catalog where and when they drive, so I can stand on the side of the street and shake my cane at them.

[brookst]

I’ve always dreamt of building a mesh network of loud vehicle detectors that would map current loud noises and track where loud vehicles live, coupled with very powerful parametric speakers. So when e.g. the network detects a loud motorcycle at 3am anywhere in town, that live sound is instantly played at high volumes targeting only homes where other loud vehicles live.

Somehow there has been little VC interest in this idea.

[warumdarum]

https://freesound.org/people/PicassoCT/sounds/850225/

Curmudgeon Ai?

[customguy]

> Use one differential side and connect it to a kitchen funnel for directional listening the other one to a plastic bottle with a very very small hole in it. It will pick up everything high frequency that's different to the environmental pressure.

Nevermind drones, and war, that's all fine; but I need to know more about this. Is there a phrase or name for this I could use to find more information, maybe example schematics?

[MiracleRabbit]

The Sensirion SDP600-25Pa speaks I2C and only has a handful of primitive commands. Add this and 3.3V and you are done.

I'm 99.5% sure if you throw Claude with a datasheet on it will Slop out working code for a ESP32 with ESP-IDF.

[amluto]

What’s the frequency response of that sensor? The datasheet says nothing.

[MiracleRabbit]

Honestly: don't know.

My experiments never had a dependency on linearity.

[ShinyLeftPad]

Doesn't wind fool this?

[MiracleRabbit]

Theoretically wind can be Nulled with a 4-way water splitter that are placed in 90° angles (+ a connector at the bottom to the sensor). As long they are orthogonal the wind pressure coming from one side will cause a counter-pressure on the opposite.

Only pressure waves coming into all holes at the same time will reach sensor.

Never tested it. Only a Gedankenexperiment as Einstein would say.

[ejanus]

Interesting! I will like to see your circuits, if any.

[MiracleRabbit]

Not much circuits needed.

The SDP600-25Pa speaks I2C and only has a handful of commands.

Just read it out with a microcontroller you love (like ESP32) and send the samples to a host for analysis. The ESP32 has limited I2C time stretching capabilities limiting it in the highest resolution modes of the sensor - but often that's not a big factor.

To not overwhelm the poor processor and Wifi maybe better a bunch of frames (like 512 or more).

[stavros]

Isn't detecting pressure waves in air exactly what microphones do?

[MiracleRabbit]

Yes. But they usually are not performing very good between 1-250Hz.

Sensirion is using a thermal flow-sensing principle method which is basically a heated plate that cools/heats up when air passes it - making it extremely sensitive in this range.