PWM Frequency and Duty Cycle in Embedded C Explained

In embedded C, PWM frequency is how often the pulse repeats per second, and duty cycle is the percentage of time the pulse stays high in one cycle. Together, they control the power delivered to devices like motors or LEDs by switching the signal on and off rapidly.

How It Works

PWM stands for Pulse Width Modulation. Imagine turning a light switch on and off very fast. The frequency is how many times you flip the switch on and off every second. For example, a frequency of 1 kHz means the switch flips 1000 times per second.

The duty cycle is like how long the switch stays on during each flip. If the switch is on half the time and off half the time, the duty cycle is 50%. If it stays on longer, say 75% of the time, the device gets more power.

In embedded C, you set these values to control devices smoothly. For example, a motor can run slower or faster depending on the duty cycle, even though the power supply is constant.

Example

This example shows how to configure PWM frequency and duty cycle on a microcontroller using embedded C. It sets a frequency of 1 kHz and a duty cycle of 50%.

c

#include <stdint.h>
#include <stdio.h>

// Assume a microcontroller with a timer clock of 1 MHz
#define TIMER_CLOCK 1000000

// Function to calculate timer counts for frequency
uint16_t calculate_period(uint32_t frequency) {
    return (uint16_t)(TIMER_CLOCK / frequency);
}

// Function to calculate compare value for duty cycle
uint16_t calculate_duty(uint16_t period, float duty_cycle_percent) {
    return (uint16_t)(period * (duty_cycle_percent / 100.0f));
}

int main() {
    uint32_t pwm_frequency = 1000; // 1 kHz
    float duty_cycle = 50.0f;      // 50%

    uint16_t period = calculate_period(pwm_frequency);
    uint16_t duty = calculate_duty(period, duty_cycle);

    printf("PWM Frequency: %u Hz\n", pwm_frequency);
    printf("Timer Period Counts: %u\n", period);
    printf("Duty Cycle: %.1f%%\n", duty_cycle);
    printf("Compare Value (ON time counts): %u\n", duty);

    // Here you would load 'period' and 'duty' into timer registers

    return 0;
}

Output

PWM Frequency: 1000 Hz
Timer Period Counts: 1000
Duty Cycle: 50.0%
Compare Value (ON time counts): 500

When to Use

Use PWM frequency and duty cycle control when you want to adjust power to devices without changing voltage. This is common in:

• Controlling motor speed smoothly
• Dimming LEDs without flicker
• Generating audio tones
• Power regulation in embedded systems

Choosing the right frequency avoids noise or flicker, and adjusting duty cycle changes how much power the device receives.

Key Points

• Frequency is how often the PWM signal repeats per second.
• Duty cycle is the percentage of time the signal is ON in each cycle.
• Changing duty cycle controls power delivered without changing voltage.
• Embedded C uses timers to set frequency and duty cycle values.
• Proper frequency selection prevents flicker and noise in devices.

Key Takeaways

PWM frequency sets how fast the signal repeats each second in embedded C.

Duty cycle controls the ON time percentage of each PWM cycle, adjusting power output.

Use timers in embedded C to configure PWM frequency and duty cycle for devices like motors and LEDs.

Choosing the right frequency avoids flicker and noise in your hardware.

PWM allows smooth control of power without changing voltage levels.