**Introduction to Stepper Motors**
A stepper motor is an electromechanical device that converts electrical pulse signals into angular or linear displacement. It receives a sequence of pulses as input and produces corresponding incremental movement or stepping motion. In normal operation, it has a fixed number of steps per revolution. When operating continuously, its rotational speed is directly proportional to the frequency of the input pulses, remaining unaffected by voltage fluctuations or load changes. Due to its compatibility with digital control, it is especially suitable for microcontroller-based systems.
**(1) Types of Stepper Motors**
There are three main types of stepper motors:
(1) **Variable Reluctance (VR) Stepper Motor**: These have a simple structure and low cost, but they offer poor dynamic performance and small step angles.
(2) **Permanent Magnet (PM) Stepper Motor**: These provide higher torque and better dynamic performance, but their step angle is relatively large.
(3) **Hybrid (HB) Stepper Motor**: Combining features of both VR and PM motors, hybrid steppers offer small step angles, high torque, and excellent dynamic performance. They are considered the most advanced type of stepper motor and are sometimes referred to as permanent magnet induction steppers.
**(2) Working Principle of Stepper Motors**
Figure X1 shows a schematic diagram of a three-phase reactive stepper motor. The stator has six evenly spaced magnetic poles at 60° intervals, with coils wound around each pole connected to A, B, and C phase windings. The rotor has 40 small teeth, resulting in a tooth pitch of 9°. Each stator pole also has five small teeth with the same pitch and width as the rotor. Because the number of rotor and stator teeth differ (30 vs. 40), there is a mismatch known as "tooth misalignment."
When the A-phase winding is energized, the rotor aligns with the A-phase teeth. Then, when the B-phase is energized, the rotor rotates 3° due to reluctance torque until the B-phase teeth align. This process continues, rotating the rotor in 3° increments. The direction of rotation can be changed by altering the sequence of the phase energization.
The step angle θb for a single three-phase operation is calculated as:
θb = 360° / (N × Er)
Where N is the number of phases, and Er is the number of rotor teeth.
**(3) Characteristics of Stepper Motors**
- Stepper motors require pulse signals to operate. Without pulses, they remain stationary.
- They can start and stop instantly, making them ideal for precise positioning.
- Changing the pulse sequence easily reverses the motor’s direction.
**How the L298N Drives a Motor**
In a stepper motor driver module, the TLP521 optocoupler provides isolation and strong interference resistance. The L297 controls the motor's direction via high/low levels, while the 18th pin serves as the stepping clock input. The 19th pin selects between full-step and half-step modes. The 10th pin enables or disables the motor. Inside, the L298N includes a high-voltage, high-current dual H-bridge driver that controls forward and reverse motion. Diodes are used for freewheel protection, and a 7805 voltage regulator supplies power to the controller and L298N. However, prolonged use may cause overheating, leading to instability.
**Key Features of the L298N Driver**
- Dual H-bridge DC and stepper motor driver chip
- Operating voltage: 4.5–5.5V
- Motor supply voltage: 5–35V
- LED indicators for power status
- PCB size: 4.4 x 5.0 cm
- Maximum output current: 2A (peak 3A), 25W power
- Freewheel diode protection included
- Can control two DC motors or one two-phase 4-wire/6-wire stepper motor
- Supports motor reversal and parallel connection for up to 3A DC motor
**L298N Stepper Motor Control Program**
Multiple diagrams illustrate the circuit layout and programming logic for controlling a stepper motor using the L298N. These images show the connections between the microcontroller, the L298N driver, and the motor itself. By sending appropriate pulse sequences, the motor moves in precise steps, either full or half-step, depending on the configuration. This setup is widely used in robotics, CNC machines, and automated systems.
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