iOS App Acoustically Measures Distances Up To 25 Meters

n01 writes "A recently published app for the iOS platform uses the propagation of sound waves to measure distances of up to 25 meters in a dual device mode. The technique works through repeatedly sending a chirp signal from the master device to which the other (reflector) device synchronizes itself and then replies in a similar fashion. A novel combination of techniques has been engineered to enhance the robustness in noisy environments, such as using an optimum-autocorrelation-signal and semi-automatic frequency calibration together with an averaging over multiple cycles."

Not impressive

[girlintraining]

That's not very impressive. Anyone who has two devices that are syncronized to a common timing source (which most cell phones are) can accomplish this. You just say "I started transmitting at x and you received it at y. x-y/speed of sound at sea level = your result. Now if it could be done with one device, and use doppler effect,etc., to map out the room and roughly what's inside it (like in Batman) then we'd be getting somewhere.

How about an echolocation app :)

[TheLink]

Some humans can learn echo location[1], but just wondering if we could have an app that sends clicks and chirps and processes the echos and creates a picture or 3D model.

But it might need two or more "ears" to quickly build a 3D image of the environment.

[1] http://www.youtube.com/watch?v=qLziFMF4DHA [youtube.com]
http://www.youtube.com/watch?v=GYWpxmcHTOc [youtube.com]

Re:Not impressive

[Solandri]

Fun story. While I was at MIT/Sea Grant working on robot submarines, we'd lay an array of underwater beacons for navigation. To conserve power, they'd listen for a certain sequence of sounds from the sub, then reply back with their unique ping. The sub could measure the time it took to receive each unique ping, and thus determine its position by using the ping times and knowledge of where the beacons were. Kind of an underwater GPS. The beacons could last a year or more when used like this, which was a big deal because it was really annoying to locate and retrieve one just to load it with a fresh battery.

On one particular deployment, we left the beacons because we were planning to return a few months later. When we got back, the beacons weren't working. We retrieved them and all the batteries were dead. So we recharged the batteries and redeployed them. After our tests were over, we left the beacons again. When we returned a couple months later, they were all dead again.

Eventually we figured it out. The dolphins in the area had figured out the sound sequence used to make the beacons respond (probably just listened in on our sub). They thought it was pretty cool to get an acoustic response every time they used that code, so they'd been merrily chirping away during those months, draining our batteries.

Re:Not impressive

[Hartree]

Mark Tilden tells a similar story about a prototype floor cleaning robot.

It took some effort to find out why it worked when he watched it, but when he came home after being away, it was always sitting still in the middle of the room without having cleaned most of the room.

The culprit: His cat would repeatedly trigger its collision avoidance sensor to make it turn away. It was a fun cat toy.

It's hard to design against active maliciousness. :)

Re:Not impressive

[Anonymous Coward]

That sounds pretty awesome. Do you know if anyone from the biology department at MIT went back there to study that behavior? Since dolphins already use echolocation to navigate, I just wonder if they were doing more than amusing themselves, and actually managed to adapt to use the beacon system for their navigation. I'm not a biologist, and don't know much about dolphins, so I don't know if that's feasible or not, but it would be pretty amazing.

Frequency?

[wisebabo]

Is there any benefit to moving to ultrasonic frequencies? Other than making it inaudible (so you don't bother people but maybe dogs!), would this improve the resolution? Does the range decrease? Do consumer level devices cover such a broad spectrum?

By the way, has anyone made an iOS or Android App that can record in the ultrasound (or infrasonic) ranges and change it so that we can listen in audible ranges? Might be neat to see/hear what the bats are doing!

Also, how DO bats build up a good 3D map of their surroundings using just one "speaker" and two "microphones"? Do they send out beams or are their ears swiveling? And, with the limited amount of computing power on a smartphone, would it be able to duplicate it? A bat's brain doesn't seem particularly large and they are doing this FAST (on the fly, ha ha).

Re:Just use a damn tape measure!

[artor3]

No, the primary use case is "oh, this is nifty, let me play with it". The accuracy is nowhere near good enough for any measurement that actually matters.

Re:Not impressive

[DriedClexler]

They didn't, because the story is bullshit.