**Introduction to Stepper Motors**
A stepper motor is an electromechanical device that converts electrical pulse signals into angular or linear displacement. The input to the motor is a sequence of pulses, and the output is a corresponding incremental movement. In normal operation, it has a fixed number of steps per revolution. When moving continuously, its rotational speed is directly proportional to the frequency of the input pulses and is not affected by voltage fluctuations or load changes. Because stepper motors can accept digital control signals directly, they are ideal for use with microcontrollers.
**(1) Types of Stepper Motors**
There are three main types of stepper motors:
(1) **Reluctance Stepper Motor (VR)** – These have a simple structure, low cost, and small step angles, but their dynamic performance is limited.
(2) **Permanent Magnet Stepper Motor (PM)** – These offer higher torque and better dynamic performance, but their step angle is larger compared to other types.
(3) **Hybrid Stepper Motor (HB)** – This type combines the advantages of both reluctance and permanent magnet motors. It offers a small step angle, high torque, and excellent dynamic performance, making it the most advanced type available today. It is sometimes referred to as a permanent magnet induction stepper motor.
**(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. Each pole has a winding connected to phases A, B, and C. The rotor has 40 small teeth, spaced 9° apart. The stator also has 5 small teeth on each pole, matching the rotor's tooth pitch. Since the stator and rotor have different numbers of teeth (30 vs. 40), there is a mismatch in tooth alignment.
When phase A is energized, the rotor aligns with the teeth under the A pole. When phase B is activated, the rotor rotates 3° due to the reluctance torque until the B pole aligns with the rotor teeth. This process continues as the phases are energized in sequence (A→B→C→A), resulting in a step angle of 3°. Changing the sequence (e.g., A→C→B→A) reverses the direction of rotation.
The step angle θb for a single-phase three-shot mode 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**
(1) Stepper motors require pulse signals to operate. Without pulses, the motor remains stationary. With the right signal, it moves in discrete steps.
(2) They can start and stop instantly, making them ideal for precise control.
(3) By changing the pulse sequence, the direction of rotation can be easily reversed.
**How L298N Drives a Motor**
In a stepper motor driver module, the TLP521 optocoupler provides isolation and interference protection. The L297 chip controls the motor’s direction via high/low signals, while the 18th pin receives the stepping clock. The 19th pin selects between full-step and half-step operation, and the 10th pin enables/disables the motor. The internal circuit includes a high-voltage, high-current double H-bridge driver (L298) to control forward and reverse motion. Diodes are used for freewheel protection, and a 7805 regulator supplies 5V to the controller and L298 chip. However, prolonged use may cause overheating, leading to instability.
**Key Features of L298N**
- Chip: L298N double H-bridge DC/stepper motor driver
- Working Voltage: 4.5–5.5V DC
- Motor Supply Voltage: 5–35V DC
- LED indicator for power status
- PCB size: 4.4 x 5.0 cm
- Max Output Current: 2A (peak 3A), Max Power: 25W
- Freewheel diode protection
- Can control two DC motors or one two-phase 4-wire/6-wire stepper motor
- Supports reversing and parallel connection for higher current
**L298N Stepper Motor Program**
The L298N driver is commonly used in projects involving microcontrollers like Arduino. It allows precise control of motor speed and direction through pulse signals. The program typically involves setting up the motor pins, defining the step sequence, and controlling the timing between steps. Diagrams and code examples are often included in tutorials to help users implement motor control effectively.
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