Well, this was my plan – to create an extremely simple virtual piano with Lego Mindstorms, just by using the ultrasonic sensor in the manner below:
To play the correct frequency for the detected key, I first tried a ladder if-then-else within the Mindstorms visual programming environment, and it absolutely tanked! For every if-then-else path, it was doubling the height and before I reached 5 such paths, the exponential growth of vertical screen height made it pathetically slow and unbelievably difficult to scroll. So I ditched it, flashed LeJos on the brick and wrote a teeny meeny Java code which worked brilliantly! or so I thought…
It was playing tunes alright, but they were not the correct ones! After a couple of rounds of troubleshooting, I quickly realized it was not any programming error, but one that I totally ignored – the resolution of the sensor!! It turns out that the precision of the sensor is +/- 3 cms, and I had the bars at 2 cm widths.
So the moral of the story is – before trying out things with sensors, make sure to read the specifications thoroughly!