A direct current motor includes a stator generating a magnetic field therein and a rotor having an armature and rotating inside the stator. The radio system and the method provide a calibration of transmit radio signals in which no dedicated calibration signal generator is required for calibrating the radio system. Moreover, the experiment results also proved that the novel light-emitting material can be applied in fabricating OLED through dry process andor wet process; so that, the novel light-emitting material is helpful to the low-cost mass production of OLEDs. The pencil sharpening slot is connected to a conical bore and a pencil chips storage room.