If the motor magnet is determined to be a magnet, then this chip may be a Hall switch. If it is not a magnet, the chip may also be a photoelectric switch or the like. The combination of the magnet and chip at the back should calculate the speed. Every time the magnetic field of the magnet rotates, the magnetic field changes twice, and the chip can sense the number of changes in the magnetic field to calculate the speed or number of turns.