In this thesis according to the exercise I figured out some ways, to measure the rev of a three phase brushless DC motor and to make this more understandable, I summarized the functioning of a motor of this kind. After this I tested the methods I chose, in depths. I simulated the circuit on a computer and then built it and did measurements with it. Afterwards I chose the most reliable and most accurate method, to make the least mistakes. I planned the circuit diagram, which includes an interface with an altimeter, a barometer and a temperature sensor besides the tachometer. From the circuit diagram I designed the printed circuit, which was sent to manufacturing and I switched to the software part of the project. Before writing the code I did a research on the SD cards, the file systems and the SDIO interface of the chosen microcontroller. According to these I wrote the program code. After this program was ready I wrote a bootloader, to be able to make firmware updates. Finally I did the functional verification of the circuit and made some future development plans.