PWM Fundamentals

TIMEEstimated Time

LEVELDifficulty

PREPrerequisites

• Multiple Buttons & State Detection You should understand digital inputs, events, and the difference between simple ON/OFF logic and structured control.

SKILLSkills You'll Learn

• Explain PWM in plain English
• Describe the difference between digital ON/OFF and PWM output
• Understand duty cycle as the percentage of time an output is ON
• Use PWM to control LED brightness
• Explain why PWM can control motor speed conceptually

PARTSComponents Required

• ESP32ESP32 DevKit boardGenerates the PWM signal
• LEDLEDShows brightness changes visually
• R220 ohm or 330 ohm resistorLimits LED current
• BOARDBreadboardHolds the LED and resistor
• WIREJumper wiresConnect GPIO18, resistor, LED, and GND
• USBUSB data cableUpload code and watch Serial Monitor

ENGEngineering Explanation

REALReal-World Analogy

WIREWiring Diagram

Follow these steps in order. Unplug USB before you change any wires.

1. 1

   Unplug the ESP32 USB cable before wiring.

2. 2

   Place the LED on the breadboard.

3. 3

   Connect ESP32 GPIO18 to one side of a 220 ohm or 330 ohm resistor.

4. 4

   Connect the other side of the resistor to the LED anode, the longer LED leg.

5. 5

   Connect the LED cathode, the shorter leg, to ESP32 GND.

6. 6

   Check that the resistor is in series with the LED, not beside it doing nothing.

7. 7

   Plug USB back in, upload the sketch, and open Serial Monitor at 115200 baud.

GPIOGPIO Table

⌨️Arduino Code

Copy this into Arduino IDE, then click Upload.

const int LED_PIN = 18;

const int PWM_CHANNEL = 0;
const int PWM_FREQUENCY = 5000;
const int PWM_RESOLUTION = 8;

void setup() {
  Serial.begin(115200);

  ledcSetup(PWM_CHANNEL, PWM_FREQUENCY, PWM_RESOLUTION);
  ledcAttachPin(LED_PIN, PWM_CHANNEL);

  Serial.println("Mission 07: PWM LED fade ready");
}

void loop() {
  for (int duty = 0; duty <= 255; duty += 5) {
    ledcWrite(PWM_CHANNEL, duty);
    Serial.print("Duty value: ");
    Serial.println(duty);
    delay(25);
  }

  for (int duty = 255; duty >= 0; duty -= 5) {
    ledcWrite(PWM_CHANNEL, duty);
    Serial.print("Duty value: ");
    Serial.println(duty);
    delay(25);
  }
}

CODELine-by-line Explanation

• LED_PIN is GPIO18, the pin connected to the LED through the resistor.
• PWM_CHANNEL chooses one ESP32 PWM channel. The channel is like a small hardware helper that creates the repeated pulses.
• PWM_FREQUENCY is 5000 Hz, which means the PWM cycle repeats 5000 times per second.
• PWM_RESOLUTION is 8 bits, so the duty value can range from 0 to 255.
• ledcSetup() configures the PWM channel with the chosen frequency and resolution.
• ledcAttachPin() connects GPIO18 to that PWM channel.
• The first for loop increases duty from 0 to 255, making the LED fade brighter.
• ledcWrite() changes the duty cycle. It does not stop the program to blink manually.
• The second for loop decreases duty from 255 to 0, making the LED fade dimmer.

WARNCommon Mistakes

• Forgetting the LED resistor

  PWM can make the LED look dimmer, but the pin still drives full current during each ON pulse.

• Thinking PWM is analog voltage

  The brightness looks smooth, so it feels like the voltage must be smoothly changing.

• Using a motor directly on the GPIO pin

  PWM motor speed examples can make beginners think the PWM pin powers the motor.

• Choosing a poor GPIO pin

  Some ESP32 pins are input-only or affect boot behavior.

• Confusing frequency with brightness

  Both are PWM settings, but they do different jobs.

!Troubleshooting

Most ESP32 problems are wiring, power, library, or timing issues. Check these first.

• LED does not turn on

  Likely cause: The LED may be backwards, the resistor may be in the wrong row, or the wire may not be on GPIO18.

  Fix: Check LED polarity, place the resistor in series, and trace GPIO18 to the resistor and LED anode.

• LED is always full bright

  Likely cause: The LED may be connected to 3.3 V instead of the PWM pin, or ledcWrite() may always receive 255.

  Fix: Confirm the LED circuit starts at GPIO18 and watch Serial Monitor for changing duty values.

• LED flickers visibly

  Likely cause: The frequency may be too low if you changed it, or delay values may make the fade look jumpy.

  Fix: Return PWM_FREQUENCY to 5000 and use small duty steps such as 5.

• Code does not compile

  Likely cause: Some ESP32 Arduino core versions changed PWM helper support.

  Fix: Confirm you selected an ESP32 board in Arduino IDE. If needed, update the ESP32 board package.

• Serial Monitor shows text but LED does nothing

  Likely cause: The sketch is running, so the issue is likely wiring or pin choice.

  Fix: Move the LED circuit back to GPIO18 and GND, then test the LED orientation.

TIPEngineer Tip

REMRemember This Forever

?FAQs

• What does PWM mean?

  PWM means Pulse Width Modulation. It controls how long a digital output stays ON during a repeating cycle.

• Is PWM real analog voltage?

  No. PWM is still digital switching. It creates an analog-like effect by switching ON and OFF very quickly.

• Why does PWM make an LED look dimmer?

  Your eyes average the fast blinking. If the LED is ON for less of each cycle, it looks dimmer.

• What is duty cycle?

  Duty cycle is the percentage of each PWM cycle that the signal is ON. 25% duty means ON for one quarter of the cycle.

• What does 0% duty cycle do?

  0% duty cycle means the output is always OFF, so the LED is off.

• What does 100% duty cycle do?

  100% duty cycle means the output is always ON, so the LED is at full brightness.

• What is PWM frequency?

  Frequency is how many PWM cycles happen each second. For beginners, think of it as how fast the ON/OFF switching repeats.

• Does higher frequency always mean brighter LED?

  No. Brightness mostly follows duty cycle. Frequency controls how fast the switching happens.

• Can PWM control motor speed?

  Yes, conceptually. A motor driver can receive PWM so the motor gets power in fast pulses, making the average speed lower or higher.

• Can I connect a motor directly to an ESP32 PWM pin?

  No. Motors need more current than a GPIO pin can safely provide. Use a motor driver or transistor circuit.

• Do I still need a resistor for a PWM LED?

  Yes. PWM changes average brightness, but the LED still needs a current-limiting resistor when it is ON.

• Why not just use delay() to blink fast?

  Manual delay blinking blocks your program and is not smooth. Hardware PWM keeps the timing steady while your code does other work.

• Does ESP32 use analogWrite() like Arduino Uno?

  Newer ESP32 Arduino cores may support analogWrite(), but learning ledcWrite() teaches the ESP32's native PWM system more clearly.

• Which ESP32 pins can use PWM?

  Many output-capable ESP32 GPIOs can generate PWM. Avoid input-only pins and boot-sensitive pins when you are just starting.

• Why does my LED flicker?

  The PWM frequency may be too low, the wiring may be loose, or the code may be repeatedly changing duty cycle too slowly.