I want to make an universal useable rotational speed sensor device. My first experiments with an infrared LED and an infrared diode which can be seen in the picture were promising. I could measure the RPM of a brushless motor and also of a propeller, just by the difference of reflections of the IR Led on the motor or propeller that got recognized by the IR diode. The Arduino code is already finished. The circuit is very simple, I didn`t even need an OpAmp.
A video about this project will come in the next days, but before I make that, I will solder everything together nicely and add a LCD to show the rotational speed.