DC motor working principle
A DC motor is a rotating electrical machine that can convert DC electrical energy into mechanical energy (DC motor) or mechanical energy into DC electrical energy (DC generator). It is a motor that can convert DC electrical energy and mechanical energy into each other.
Current DC motors are all rotating armature type, mainly composed of a rotor and a stator. The stator includes main magnetic poles, commutating magnetic poles, brush assembly, frame, and end covers; the rotor has an armature core, armature windings, commutator, shaft, and bearings. As the name suggests, the stator is the stationary part that generates a fixed magnetic field; the rotor is the rotating part that generates a magnetic field with changing polarity. This is a physical model diagram of a DC motor. The stationary part contains magnets, referred to here as main magnetic poles; the stationary part also contains brushes. The rotating part has a toroidal core and windings wound around the toroidal core.
A magnetic field exists around a current-carrying conductor, and the conductor experiences the Ampere force (the force exerted on a current-carrying conductor in a magnetic field). Because direct current flows through it, a polarity opposite to the main magnetic pole is generated, causing the conductor to move in one direction. When the rotor of a motor rotates 180 degrees under this force, the motor brushes automatically reverse the direction of the current, allowing the rotor to continue rotating. This can be understood by recalling the repulsion and attraction of like poles to magnets. This is the basic working principle of a DC motor.
Implementation method
Motors are current-driven components that require a large current flow. Traditional microcontroller I/O outputs typically have an output current of around 10mA, while modern microcontrollers generally output 20-25mA. However, the total current across multiple I/O ports is limited; some cannot exceed 200mA, while others cannot exceed 400mA. For example, a DC motor with a rated voltage of 12V and a rated power of 25W requires a working current of 2A, or 2000mA. The driving capability of a microcontroller's I/O ports is far from sufficient. Therefore, a driver device is needed to control the motor. Here, we choose the ULN2003, a high-voltage, high-current driver chip composed of seven silicon NPN Darlington transistors. Simply put, the ULN2003 amplifies the current output from the microcontroller's I/O ports; for a microcontroller to drive a motor, it must utilize a driver like the ULN2003.
DC motors have only two terminals, making wiring very simple. Simply put, connect one terminal to the positive terminal of the power supply and the other to the negative terminal, and it will rotate. To make the motor rotate in the opposite direction, simply reverse the polarity. The schematic diagram for connecting it to a microcontroller is shown below:
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