Wouldn’t it be amazing to have a ruler in your pocket all the time? Well now you can! Measure distances of up to 25 meters (82 feet) with Acoustic Ruler Pro for the iPhone, iPod touch, and iPad (App Store Link). Scroll down for the details or watch the two videos showing the two different operation modes first:
This video shows the dual device mode with two iPod touch devices:
This video shows the single device mode with an iPad:
The app works by clocking the time delay of the emitted sound waves. There are two different operation modes: a single device operation (with headphones) and a dual device mode for measuring the distance *between* two devices. Read below to find out which modes work on your iOS device.
Single device (headphone) mode:
This mode works on the iPhone 3GS (and newer), iPod touch 3rd Generation (and newer) and on all iPads. You either need one of those devices and headphones with a mic or headphones without a mic and a iOS device with a built-in mic (excluding the iPod touch 3rd Generation). The resolution in this mode is 1mm or 1/10 of an inch, depending on the unit system you have selected.
Dual device mode:
For this mode you need two compatible iOS devices. These are: iPhone 3GS (and newer), iPod touch 4th Generation and all iPads. One device has to be started as the master device, and the other as the reflector device. The measurement is started on the master device, by pressing the “Measure” button. The reflector device then sends back the chirp of the master which displays the measurement result. The resolution in this mode is 1cm or 1/2 of an inch.
When you first start the program, it will guide you through the easy calibration steps with text and illustrations explaining what to do. Please recalibrate when you are getting wrong measurements.
The app lets you set the air temperature as an additional calibration. This is important, because the speed of sound varies considerably with temperature, affecting the precision of the measurements.
You can switch between displaying the measurement in feet/inches and meters/centimeters. Accordingly, the air temperature will either be set in degrees fahrenheit or celsius.
Please note that while the resolution of the measurements may be as low as 1mm and I have taken great care to make the app as reliable as possible, there are simply too many factors affecting the measurement process and the accuracy. That’s why there is no warranty that the measurements taken with Acoustic Ruler Pro are 100% correct. Since the app works by sending and receiving sound, you’ll obviously get the best results when using it in an environment that is not too loud.
If you have any problems with the app, please leave a message below or via Twitter (preferably before giving the app a negative review). I will do what I can to get the app running perfectly on your device! Customer satisfaction is very important to me.
Follow @acoustic_ruler on Twitter to stay up to date with the newest developments, or to report any problems you may have.
Acoustic Ruler on cheap hardware
I regularly get inquiries from companies and individuals who are interested in acoustic distance measurement. In most cases it is not an option to buy two iPod touch devices. That’s why I’m trying to get my acoustic distance measurement method running on the cheapest possible hardware.
In the video you see my messy desk and the C5535 eZdsp USB Stick Development Kit from Texas Instruments. On the small OLED display, the left number is the measurement in millimeters. I have since abandoned the DSP route because of new plans for making it work on even cheaper hardware.