Sonic ruler app created for iPhone

Uses pulses of sound to determine distance

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21 August 2009 11:14 GMT / By Duncan Geere

Wanna get a decent approximation of a distance, but haven't got a tape measure handy? A North American developer called Laan Labs has built an application that uses the phone's speaker to take sonic measurements.

For those of you who aren't too familiar with A-level physics, here's how the app works. When the sound pulse is generated, a timer starts. The microphone listens, and when it hears the signal bouncing back, it stops the timer. Then, knowing the approximate speed of sound, you can work out the distance using good old "speed equals distance over time".

As the sound could be bouncing off lots of other things too, the app does this lots of times and graphs the results. It then displays the peak of that graph, which should - in most situations - be whatever you're pointing the handset at. You'll get results as long as the phone can hear the echo, so it's probably got a practical limit of ten metres or so in the real world.

There's a few sources of error - wind would affect the measurement because it would blow sound around, and the temperature of air will affect how fast sound travels through it, but neither should prove a huge problem. Still, the developer recommends that you don't use it for anything "other than your entertainment".

The developer says: "I think a lot of things could be improved in the app like better echo detection or user interface. I'd like to post the code, but it's kind of mangled right now so I may wait until I can clean it up a bit".

The application costs 59p, and it's available now.