A trivial application of ultra cheap Chinese ultra-sonic modules like the US-020, is to use it as range finders. The question is what is the maximum distance we can measure. These modules have an on board microprocessor and so we don't have any access on front end receiving amplifiers or transducer driver stages. The signals we get are pre-processed. A search through the available cryptic manuals on the net depicts a polar diagram that shows max distance about 10' (~300cm) which is far less than the 400-500cm advertised on ebay.
We wanted our setup to be portable in order to have some outdoors measurements. So we connected our arduino mini to a linvor slave bluetooth module and used our mobile android phone as a terminal using an excellent free android application named Bluetooth SPP by Jerry Lee. Bluetooth SPP realises the SPP bluetooth service on an android device and is rock solid, much more robust than standard microsoft SPP service on ms Win XP BT stack. Plus, it includes a file logger !! At first we measured a distance of approx 5 metes and we certified it with a laser rangefinder. Accuracy is pretty good (within 1 cm ) for such a low priced device and consistency is impeccable as you can see in the following video.
Searching for the maximum distance in a noisy outdoors environment was quite difficult. We used an office chair to be able to rotate the measurement setup on the horizontal plane. At last we could get 1009 cm as the maximum reading in our terminal while 1135 cm seems to be our maximum software limt. Accuracy was in the range of 5cm and consistency was not bad at all using a simple software filter that rejected erratic measurements.
