[graycat]

Do something with audio: The iPhone has speakers, right? And software can send a signal to the speakers? Or if not speakers, then a female plug can use to drive speakers? And the thing has a microphone, right? And might add on some tubes or some such to make the speaker and microphone directional? For the signal to make the signal to noise ratio better and to make the sound more directional, use high frequency. Or just build a little ultrasonic attachment that sends out the signal and get back the reflected signal.

Distance to the wall? Sure, the first and strongest part of the reflected signal will be from the line from the iPhone to the wall that is perpendicular to the wall (that's the shortest distance), and that's what is wanted.

But as I recall, there are laser distance measuring devices available for carpenters, surveyors, etc.

[ay]

https://iqtainment.wordpress.com/acoustic-ruler/

I've played with it - with some calibration, it seems to work. But YMMV, and I got it mostly just in an appreciation of the author's clever idea.

[graycat]

Fantastic! I was just guessing and didn't know someone had already done it!

Thanks!