Introduction
Control DC motor speed and direction using PWM signals with L298N H-bridge and closed-loop PID controller. This comprehensive guide covers everything from design through implementation, testing, and deployment.
Motor Speed Control using PWM
Control DC motor speed and direction using PWM signals with L298N H-bridge and closed-loop PID controller.
DifficultyBeginner
Duration1–2 weeks
Components10 items
Steps6 steps
Theory & Background
PWM (Pulse Width Modulation) controls the average voltage delivered to the motor by rapidly switching a fixed supply voltage on and off. At 50% duty cycle, the motor receives 6V average from a 12V supply. Increasing duty cycle increases average voltage and therefore speed. The L298N H-bridge allows current to flow in either direction through the motor, enabling both forward and reverse direction control by toggling the IN1/IN2 logic inputs.
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Components & Requirements
10 components required for this project.
| # | Component | Purpose | Qty |
|---|---|---|---|
| 1 | Arduino Uno | PWM signal generation and PID control | x1 |
| 2 | L298N H-Bridge Module | Motor driver capable of bidirectional control | x1 |
| 3 | DC Motor (12V, 3000 RPM) | Controlled load | x1 |
| 4 | Rotary Encoder (600 PPR) | Speed feedback for closed-loop control | x1 |
| 5 | 10kΩ Potentiometer | Speed setpoint input | x1 |
| 6 | 12V 2A Power Supply | Motor power | x1 |
| 7 | 0.1µF Decoupling Capacitors | Motor noise suppression | x4 |
| 8 | 1N4007 Flyback Diodes | Back-EMF protection (if using discrete H-bridge) | x4 |
| 9 | OLED Display 0.96" | Speed display | x1 |
| 10 | Heatsink for L298N | Thermal management | x1 |
Step-by-Step Implementation
Follow these 6 steps carefully.
1
Understanding PWM and Motor Control
PWM (Pulse Width Modulation) controls the average voltage delivered to the motor by rapidly switching a fixed supply voltage on and off. At 50% duty cycle, the motor receives 6V average from a 12V supply. Increasing duty cycle increases average voltage and therefore speed. The L298N H-bridge allows current to flow in either direction through the motor, enabling both forward and reverse direction control by toggling the IN1/IN2 logic inputs.
2
Hardware Connections
Connect L298N: ENA pin to Arduino PWM pin (pin 9), IN1 to pin 7, IN2 to pin 8 for motor A direction control. Connect 12V motor supply to L298N power input (remove 5V jumper). Connect encoder VCC to 5V, GND to GND, and A/B channels to Arduino interrupt pins 2 and 3. Wire potentiometer middle pin to A0 for speed setpoint.
3
Encoder Interrupt and Speed Calculation
Attach interrupt to encoder channel A: attachInterrupt(0, encoder_ISR, RISING). In ISR, increment pulse counter. Calculate RPM every 100ms: RPM = (pulse_count × 60) / (PPR × time_seconds). For 600 PPR encoder with quadrature decoding: RPM = (pulses × 60 × 1000) / (600 × dt_ms). This gives real-time speed feedback for the PID controller.
4
PID Controller Implementation
Error = setpoint_RPM - actual_RPM. P_output = Kp × error. I_output += Ki × error × dt (integrate error over time). D_output = Kd × (error - prev_error) / dt. PID_output = P + I + D, clamped to 0–255 for analogWrite. Start tuning: Kp=0.5, Ki=0.01, Kd=0.05. Increase Kp until oscillation, then reduce 30%, add Ki to eliminate steady-state error, add Kd to reduce overshoot.
5
Direction Control Logic
Set forward: IN1=HIGH, IN2=LOW, ENA=PWM. Set reverse: IN1=LOW, IN2=HIGH, ENA=PWM. Stop: IN1=LOW, IN2=LOW (coast) or IN1=HIGH, IN2=HIGH (brake). When changing direction, ramp speed down to 0 first to prevent motor and driver stress. Implement software braking by briefly applying reverse PWM to decelerate quickly — useful for precise position applications.
6
Soft-Start and Overspeed Protection
Never command full speed instantly from stop — the inrush current can trip the power supply and stress gears. Implement a soft-start: ramp the PWM from 0 to setpoint over 2 seconds. Set a maximum RPM limit in code: if actual RPM > max_RPM (e.g., 2800), override PID output and reduce duty cycle. Monitor L298N temperature; if the module is too hot to touch, reduce maximum duty cycle by 10%.
Code & Implementation
Core code for motor_pid.ino:
motor_pid.ino
C/C++
volatile long encoderCount = 0; float kp = 0.8, ki = 0.02, kd = 0.05; float setpoint = 1000; float integral = 0, prevError = 0; void encoderISR() { encoderCount++; } float getRPM() { static long lastCount = 0; static unsigned long lastTime = 0; unsigned long now = millis(); long count = encoderCount; float rpm = ((count - lastCount) * 60000.0) / (600.0 * (now - lastTime)); lastCount = count; lastTime = now; return rpm; } void loop() { setpoint = map(analogRead(A0), 0, 1023, 0, 2800); float actual = getRPM(); float error = setpoint - actual; integral += error * 0.1; integral = constrain(integral, -100, 100); float derivative = (error - prevError) / 0.1; float output = constrain(kp*error + ki*integral + kd*derivative, 0, 255); prevError = error; analogWrite(9, (int)output); delay(100); }Testing & Troubleshooting
Test Motor Speed Control using PWM by verifying each subsystem individually before full integration.
Troubleshooting Tips
Verify power voltages, check ground connections, use serial monitor for debug.
Real-World Applications
DC servo motor positioning
Conveyor speed regulation
Fan and pump variable speed
Electric toy/vehicle drivetrain
Camera gimbal motor control
3D printer extruder motor
Robotic arm joint control
DIY CNC axis drive
Extensions & Next Steps
- Implement full PID auto-tuning algorithm
- Add encoder-based position control for servo-like operation
- Scale up to 3-phase BLDC motor control
- Build a multi-axis synchronized drive system
- Implement regenerative braking energy recovery
Interactive Playground
Coming SoonAn interactive simulator will be available here — simulate circuits and run code in-browser without hardware.
Frequently Asked Questions
Why does my motor vibrate at low PWM duty cycles?
At very low duty cycles (below ~15%), the PWM on-time may be shorter than the motor's mechanical time constant, causing it to stutter rather than spin smoothly. Solutions: increase PWM frequency to 20–30kHz (above audible range) using Timer1 direct register manipulation to eliminate audible whine, add a small amount of minimum duty cycle to ensure the motor is always slightly above its friction threshold, or use a linear amplifier instead of PWM for very low speed applications.
What is the difference between coast and brake in motor stopping?
Coast: set both IN1 and IN2 LOW — both H-bridge switches open, motor terminals float, motor decelerates purely through friction — slow stop. Brake: set both IN1 and IN2 HIGH — both motor terminals connected to ground (short-circuit braking) — motor's back-EMF drives current through its own windings, creating strong opposing torque for rapid deceleration. Brake is preferred for precise positioning; coast for gentle stopping.
Can L298N control stepper motors too?
Yes — the L298N can drive bipolar stepper motors using both H-bridge channels (Channel A and B). For a 4-wire bipolar stepper, connect the two coil pairs to the two motor output channels. Generate the 4-step or 8-step (half-step) sequence using digital output pins in the correct order. However, L298N has no microstepping capability and its 2V voltage drop limits efficiency — dedicated stepper drivers (A4988, DRV8825) are preferred for steppers.
What causes L298N to get very hot?
L298N is a bipolar junction transistor (BJT) H-bridge with approximately 2V voltage drop per switch. At 2A motor current, each switch dissipates 4W — up to 8W total in the IC. This is very inefficient compared to MOSFET-based drivers (0.1V drop). Mitigate: attach a large heatsink, reduce maximum current if possible, consider replacing with a MOSFET-based driver (BTS7960, DRV8876) for higher efficiency and lower heat.
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