What Is PWM? Arduino Frequency and Duty Cycle Examples

Short answer: we control the time it is on

PWM is a pulsed output whose high time portion changes. Frequency tells how many cycles we have per second and Duty Cycle tells what proportion is on in each cycle. Changing one does not necessarily change the other. In the 5V output with Duty equal to 50%, the signal goes between Low and High; The output is not constant 2.5V all the time.

The example code in this article is for the Arduino Uno R3. Do not generalize the behavior of timer and PWM base to Uno R4, ESP32 or STM32. The accompanying graph is an ideal mathematical waveform and not an oscilloscope picture or actual board test result.

Calculate period, frequency and duty

Average does not explain all load behavior. Motor, resistor, LED and digital input do not respond the same to the same pulse. The actual range of the GPIO is also not assumed to be equal to the power rail under load; Check the allowable current of base and driver separately.

Uno example: five timed lighting commands

For low current test, connect a common LED with a 1 kΩ series resistor from D9 to the LED anode and cathode to GND; Disconnect power before wiring. Do not connect high power LED, LED strip or motor to GPIO. For them, a suitable driver and a separately designed source are required.

The program gives the next command every two seconds: zero, 64, 128, 192 and 255. For the Uno R3, the default analogWrite API uses the range 0 to 255. Pin 9 is around 490 Hz in the default setting of the AVR core; The 500 Hz waveform is just to simplify the calculation. The reference analogWrite details the boards separately.

#include <Arduino.h>
#if !defined(ARDUINO_AVR_UNO)
#error "This example is qualified for Arduino Uno R3 only."
#endif
constexpr uint8_t PWM_PIN = 9;
constexpr uint8_t LEVELS[] = {0, 64, 128, 192, 255};
uint8_t nextLevel = 0;
uint32_t lastChange = 0;
void setup() {
  pinMode(PWM_PIN, OUTPUT);
  analogWrite(PWM_PIN, 0);
  Serial.begin(115200);
  lastChange = millis();
}
void loop() {
  const uint32_t now = millis();
  if (uint32_t(now - lastChange) < 2000UL) return;
  lastChange = now;
  const uint8_t value = LEVELS[nextLevel];
  analogWrite(PWM_PIN, value);
  Serial.print(F("PWM command (0..255): "));
  Serial.println(value);
  nextLevel = (nextLevel + 1) % (sizeof(LEVELS) / sizeof(LEVELS[0]));
}

The printed number is the "PWM command", not the measured brightness. The human eye does not have a linear response; Doubling the steering is not necessarily doubling the perceived brightness. The code is compiled for the Uno R3; Physical LED test is not done.

Higher frequency is not always better

Low frequency may cause flickering or audible noise; Higher frequency also increases the number of switching, losses and driver requirements. In many timers, the number of counts per cycle is split between frequency and duty cycle. Read the exact limit from the timer of the same MCU.

On the Uno, changing the timer setting can interfere with timing libraries or functions. The code above does not reset the timer. If you are using a motor or an inductive load, energy containment and gate behavior belong to the power section; Article NMOS and PMOS and ESP32 Resets: Brownout and Power Supply Troubleshooting See also

Does the output become smoother with the RC filter?

For an impedance input, a low-pass filter can reduce the fast PWM component, but the output still has ripple and settling time. An ideal example of R=1 kΩ and C=10 µF gives a time constant of 10 ms and a cutoff frequency of about 15.9 Hz. Five time constants are approximately 50 ms; This number is ideal for the step response of the model without additional load.

tau = R * C
fc = 1 / (2 * pi * R * C)
R = 1000 ohm; C = 10e-6 F
tau = 0.010 s; fc = 15.915 Hz

If the load has low resistance, both the final level and the response will change. A small RC is not a load power source. Compare ripple, tolerance, buffering and DAC requirements for accurate analog output. The accompanying calculation file shows the average difference and model ripple.

Common errors in measurement and use

For checking, record command, observed duty, frequency, current and driver temperature separately. Do not make a thermal confirmation of a product from a part not heating up in a few seconds.

Common questions

To execute multiple tasks simultaneously without a two-second pause, structure the program in Arduino programming without delay; Read millis and multitasking.

Official sources and accompanying files

Technical resources were reviewed on 10/13/2026. Match the version and model of your part with the related document.

• Arduino; analogWrite
• Arduino; The official text of the reference and table of wins

Get the decision sheet and test registration (CSV); The full package of the article and accompanying files are available from the download section of this page.