Meet Drone Shield, an Ambitious Idea For a $70 Drone Detection System

An anonymous reader writes "Here's an Interesting idea of how to use a Raspberry Pi and a few other inexpensive items to make a low cost detection system. From the article: 'The Drone Shield would combine a Raspberry Pi, a signal processor, a microphone, and analysis software to scan for specific audio signatures and compare them against what known drones sound like. (Because obviously a Predator drone is going to sound very different than a small quadcopter.) Once a match is found, the Drone Shield then sends an e-mail or SMS to its owner...'"

Comments

Range

[Dan East]

A Predator has an operating ceiling of 25,000 feet. You think a raspberry pi and mic is going to hear a Predator drone in cruise mode that's 5 miles above? You can't even hear a massive passenger jet at that altitude! Now a quadcopter is a different story, as they are as loud as can be, but saying this system would work on something like a Predator is a stretch.

Re:Range

[Anonymous Coward]

Yeah, you'll need some bigger tools for that.

Re:Range

[Anonymous Coward]

So now the highly directional microphone has to be pointed toward the undetected drone in order to detect it? That makes perfect sense.

Re:Range

[fluffy99]

So now the highly directional microphone has to be pointed toward the undetected drone in order to detect it? That makes perfect sense.

If you're sophisticated and have multiple microphones in a well planned array, then you can aim your microphone in software and sweep the sky looking for the signature. Look up acoustic beam-forming. If the array is large enough you can estimate distance as well as angle. The bonus is that you get actual tracking instead of just detection.

The problem would be processing power though. Simple implementations could range from 4 microphones that you sum/subtract to look at quandrants, up the way to something approaching what the US Navy does with its towed arrays. I doubt the PI could handle the processing of the signals in both the time domain to get tracking, and the frequency domain to do target qualification.

Of course you also have the question of what do you do when you detect one? Aim a camera at it? Fire off your green laser? (no not suggesting you commit a felony).

Re:Range

[Cryacin]

Dusts off old chestnut

Sounds like you need a beowulf cluster for that!

Re:Range

[DerekLyons]

Disclaimer, I was a submarine crewman and though I was a qualified sonar watchstander I was not a sonar tech. I have also studied fairly widely in the unclassified literature.

So now the highly directional microphone has to be pointed toward the undetected drone in order to detect it? That makes perfect sense.

If you're sophisticated and have multiple microphones in a well planned array, then you can aim your microphone in software and sweep the sky looking for the signature. Look up acoustic beam-forming. If the array is large enough you can estimate distance as well as angle. The bonus is that you get actual tracking instead of just detection.

It's certainly simple - in theory. In reality, picking out such a faint noise from the background is Very Difficult Indeed.
 

The problem would be processing power though. Simple implementations could range from 4 microphones that you sum/subtract to look at quandrants, up the way to something approaching what the US Navy does with its towed arrays. I doubt the PI could handle the processing of the signals in both the time domain to get tracking, and the frequency domain to do target qualification.

Processing power, both for signal analysis (finding the faint signal) and for beamforming is on the beginning of your problems. Let's just hit the high spots:

• The accuracy of your track is only as good as the accuracy of your microphone positioning. (You won't need surveyor grade accuracy, but you will probably need better than the three meter accuracy that WAAS/GPS provides.) You can't beamform if you don't know the relative locations of your microphones. Oh, and did I mention that sound is refracted as the temperature of the air changes? You'll have to account for that too - assuming you can get accurate enough data on current conditions.
• You'll need some fairly clever filtering and processing to avoid the microphones being swamped by unrelated and louder background noise.
• You also need high quality low noise amplifiers to bring the sound of Predator up to useable levels. (The highest quality commercial audiophile amplifier isn't even close. You need a supercomputer and audiophile gear by comparison isn't even as good as the throwaway calculators you get with your breakfast cereal.)
• Speaking of the sound... different frequencies get attenuated and refracted differently. You'll have to account for that too.

Etc... etc... The very definition of a non trivial project. You're essentially trying to replicate what the USN does with it's passive sonar systems, with dull and chipped stone knives. (You don't even have a bearskin. You don't even get a bearskin, just the aforementioned knives.)

Tough

[Cassini2]

It's tough to reliably detect low-level background repetitive noise without detecting all sorts of nearby domestic appliances, car engines, and such. In the modern city, we live with *alot* of noise.

Now, if the problem is to detect jet engines in rural areas featuring mountainous terrain, then I think I know what the point of this project is.

Re:Interesting...

[BitZtream]

It is much more developed, you just don't realize it. This sort of signal processing is used in ultrasound machines, your car, my boat, fetal heartbeat monitors, little credit card readers that attach to your phone via headphone jacks. ALL SORTS OF STUFF.

Its all just an application of some FFTs and some weighting. It isn't even non-trivial for anyone with some basic understandings.

Without any prior knowledge, I went from no understanding to of FFTs to writing code to detect lean fuel during runtime on my R/C airplane. A Raspberry PI is also way more CPU power than needed to do it, which means it can also do a whole bunch of other stuff too.

Re:Cardinal vs. Mockingbird vs. Bluejay

[ceoyoyo]

Hm. That might be interesting. Build a couple and put them a distance apart, plus a remote controlled super soaker. Sit in the basement and pretend it's a sub.

"Skipper, we have a contact on bearing 238... probable squirrel class mammal, likely a grey!"

"Do you have a firing solution?"

"Range and course calculated skipper! Firing solution locked in!"

"Fire!"

"Skipper, sudden change of aspect on the contact. I have angry squirrel sounds."

"Nice job, everybody."

Re:Interesting...

[Black Parrot]

A Raspberry PI is also way more CPU power than needed to do it, which means it can also do a whole bunch of other stuff too.

My ++ model will mine Bitcoins between drone attacks!

Re:Interesting...

[Cryacin]

Funny will be when they mount these drone shields, on drones. Then the drone shields will be warning you about other drone shields operating in the area.

Re:Bigger tools -- was Re:Range

[KGIII]

I don't think that I disagree with your ideals. Having said that, and - really, I don't disagree with them in all likelihood, I must ask, "In which way(s) are you asserting that drones, or their use(s), illegal to start with? What, specifically, is illegal about drones? What laws are being broken with them?"

I ask because, well, I fear that they will become so inexpensive to operate (including training) that they will be used to increase surveillance which, while against my ideals, probably doesn't (in and of itself) violate any laws. I'd like to be able to make a clear, factual, and reasonable argument against the increased use of drones but I don't have any arguments to make against it that are logical and truthful. I can only state that I'm afraid of what it may turn into.

Even in my worst imagined fears concerning these drones, I'm unable to find any laws that are being broken. Perhaps you come from a different country than I do? I'm from the United States of America. We're not all that free here which means that there are a lot of laws. Given the number of laws it is impossible for me (I'm not a lawyer, even then it would still be impossible) to know all of the laws. However, I'm reasonably aware of the many laws that we have to protect us and I'm reasonably aware of the laws that the government must follow and I'm unable to point to anything specifically about drones (or their proposed use, or even with the uses that I'm afraid of) which are illegal.

So, I'm not asking you to be my research assistant or the likes. You stated that drone use was illegal which isn't very specific and certainly isn't true so I'm hoping that you have something more concrete and that you can actually point out which laws being broken by these. If you could provide specifics and case law that would be most excellent too but I'm trying to not ask for too much.

See, in my opinion, they are making their surveillance too intrusive and too easily accomplished. In this day and age we're able to be monitored in most everything we do and, while this has always been legal, it has become increasingly easy for this to be done and for this information to be shared. The use of drones by police, municipalities, and private companies to monitor, photograph, and track a person is just yet another step in the age of zero privacy. I'm quite certain that it (that portion specifically) is legal though I'm equally certain that it shouldn't be. I can vocalize, express, this as a worry and all and that may affect the opinions of some but if it is illegal then there's an even greater chance of demonstrating the harm that this can cause to society.

I don't know... Perhaps you meant it should be illegal? I'm really unable to find anything that indicates the use of drones would be illegal in and of itself and that includes FAA regulations and the likes - I've looked. I could be missing something. Then again, this is /. and you could just be an insane zealot who thinks that anything they don't like is illegal but I'm hoping you're more honest and logical than that. Trust me on this, I've seen it here before...

Either way, I'm hoping you have something more concrete than the generic statement that the use of drones is illegal because, well... No, no it isn't illegal in and of itself. If there's some specific manner that they're being used that is illegal then I'm quite interested in knowing what it is. Like I said, I've even met people online who thought that DST (Daylight Savings Time) was illegal so you could just be one of the crazy ones but I'm sort of hoping you're not. It would be, admittedly, amusing but it wouldn't actually be beneficial to me.