The project came about when he needed to test the top speed of a stepper motor. After putting it together the project became an important diagnostic tool for a larger project – not only does it test the top speed of stepper motors but it also works as a tool to verify code.
The tachometer measures rotational speed using only simple light sensor with an op-amp comparator circuit. While many mechanical engineers might cringe at the thought of an op-amp, Elliot’s team found a tutorial that explained them well.
A question was recently asked on the forum, how fast can attachInterrupt count pulses. I did some testing to find out, and made this video.
Turns out Teensy 3.2 can run about 1.25 million interrupts per second. Teensy 3.6 can do about 2.55 million per second. But these depend on assigning a top priority to the interrupt, as explained in the video.
Of course, both boards can use a timer to count pulses at very high rates, at least 30 MHz.
The project came about when he was having difficulty getting an expensive input board to work in a haunted house attraction. When he discovered that the iCade keyboard commands worked over a USB connection, he figured he could use an Arduio board and hood the USB side to an iPad and create his own interface. With a bit of research he got his project up and running.