STM32 PWM Principle and Application

PWM (Pulse Width Modulation) is a fundamental technique used in STM32 and other microcontrollers for controlling analog-like behavior using digital signals. It is widely used in applications such as motor control, LED brightness, audio signal generation, and more.

🔧 STM32 PWM Principle

✅ What is PWM?

PWM is a digital signal with a fixed frequency but variable duty cycle.

• Frequency: How often the signal repeats (e.g. 1 kHz = 1000 times per second)

• Duty Cycle: The percentage of time the signal is HIGH in one period.

Example:

• 0% Duty Cycle → Always LOW

• 50% Duty Cycle → Half HIGH, half LOW

• 100% Duty Cycle → Always HIGH

✅ How STM32 Generates PWM

STM32 uses Timers in PWM mode to generate signals:

1. Timer counts up to a value (ARR - Auto Reload Register).

2. When counter reaches a compare value (CCR - Capture Compare Register), the output pin toggles.

3. The compare value defines the duty cycle.

📐 PWM Formula

For a timer in up-counting mode:

• PWM Frequency = Timer Clock / ((PSC + 1) * (ARR + 1))

• Duty Cycle (%) = (CCR / ARR) * 100

Where:

• PSC = Prescaler

• ARR = Auto Reload Register

• CCR = Capture Compare Register

🛠️ Application Example: LED Brightness Control

🧱 Hardware

• STM32F4 board

• LED connected to a PWM-capable pin (e.g., TIM3_CH1)

⚙️ Setup in STM32CubeMX

1. Select Timer (e.g., TIM3)

2. Enable a PWM Channel (e.g., CH1) on a pin (e.g., PB4)

3. Set the timer prescaler and period (ARR) to define frequency.

4. Enable GPIO as alternate function.

5. In the generated code, use __HAL_TIM_SET_COMPARE() to control duty cycle.

📄 Example Code

🎯 Common Applications

📚 Conclusion

PWM in STM32 is implemented using timers, offering high precision and flexibility. It's simple to configure with CubeMX and powerful enough for real-time control tasks like dimming, speed regulation, and signal generation.