Control LED Brightness with Potentiometer

Key Concepts

• Analog-to-Digital Conversion (ADC): Reading the continuous voltage from the potentiometer.
• Pulse Width Modulation (PWM): The technique used by the ESP32 to fake an analog voltage output on a digital pin, controlling the LED’s brightness.
• Mapping: Converting a large range of input values (0-4095) into a smaller output range (0-255).

Circuit Connections

Components	ESP32 Dev Module
Potentiometer	GPIO34
LED (Red)	GPIO16

IMPORTANT: The ESP32’s ADC is most stable on the dedicated input-only pins like GPIO 34-39. Using GPIO 34 for the potentiometer is highly recommended.

Logic Flow

1. The user rotates the potentiometer knob.
2. The rotation changes the voltage on the middle pin of the potentiometer.
3. The ESP32 uses analogRead(34) to convert the voltage into a digital value (ranging from 0 to 4095).
4. The map() function scales this 0-4095 range to the 0-255 range required for PWM brightness.
5. The ledcWrite() function sends the new brightness value (duty cycle) to GPIO 16. The LED changes brightness proportionally, providing immediate visual feedback.

Code Lab

Step 1: Install Libraries

No external libraries are required! The ESP32’s functions for ADC (analogRead()) and PWM (ledcSetup(), ledcWrite()) are built-in features of the ESP32 core in the Arduino IDE.

Step 2: Copy and Paste Code

Copy and paste this code into the Arduino IDE:

const int potentiometerPin = 34; // Analog input for the Potentiometer (ADC Pin)
const int ledPin = 16;         // Digital output for the LED (PWM Pin)

const int ledChannel = 0;      // Use PWM channel 0
const int freq = 5000;         // Set frequency to 5 KHz for stable operation
const int resolution = 8;      // 8-bit resolution gives a duty cycle range of 0-255

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

  // ledcSetup(channel, frequency, resolution_bits)
  ledcSetup(ledChannel, freq, resolution);

  // ledcAttachPin(pin, channel)
  ledcAttachPin(ledPin, ledChannel);
  
  Serial.println("Analog Light Dimmer System Initialized!");
}

void loop() {
  // Read the analog value(Range: 0 to 4095)
  int potValue = analogRead(potentiometerPin);

  // 2. Map the large input range (0-4095) to the smaller PWM output range (0-255)
  int brightness = map(potValue, 0, 4095, 0, 255);

  // 3. Write the new brightness (duty cycle) to the LED pin
  // ledcWrite(channel, duty_cycle_value)
  ledcWrite(ledChannel, brightness);

  // Output values for verification
  Serial.print("Raw ADC Value: ");
  Serial.print(potValue);
  Serial.print(" -> PWM Brightness: ");
  Serial.println(brightness);

  delay(10); // Small delay for stable readings and output
}

Step 3: Upload and Run

1. Connect your ESP32 board and ensure the correct board and port are selected.
2. Upload the code.
3. Open the Serial Monitor at 115200 baud.
4. Rotate the potentiometer knob and observe the LED and the serial output.

System Check

Troubleshooting Guide

Problem	Observation	Solution
LED is always ON or OFF	The LED does not dim or change state, regardless of the knob position.	Check LED Pin: Ensure the LED is connected to GPIO 16. Verify PWM Setup: Confirm ledcSetup and ledcAttachPin are called correctly in setup().
Potentiometer reading is stuck	Raw ADC Value is always 0 or 4095 in the Serial Monitor.	Check Wiring: Verify the middle pin is on GPIO 34.
Light is erratic/flickers	The LED brightness is unstable, or the values jump.	Try increasing the delay(10) to 50 or 100 milliseconds.
Code fails to upload	Errors related to the ESP32 board or port selection.	Board Selection: Confirm the ESP32 Dev Module is selected under Tools > Board. Check the Tools > Port setting.

How It Works

Analog-to-Digital Conversion (ADC)

The potentiometer acts as a voltage divider, providing a voltage between 0 and 3.3 (the ESP32’s operating voltage). The ESP32’s ADC reads this voltage and converts it into a digital number. The default resolution is 12-bit, resulting in a value range from 0 to 4095.

PWM and the map() Function

• The PWM technique rapidly switches the LED pin ON and OFF. The duty cycle (percentage of time spent ON) determines the apparent brightness.
• We set the PWM resolution to 8-bit in ledcSetup(), giving us a final duty cycle range of 0 to 255.
• The map(potValue, 0, 4095, 0, 255) function linearly scales the raw 0-4095 input from the pot down to the $0-255$ output required for the LED’s brightness, making the knob control perfectly smooth.

LEDC API

The ESP32 uses the ledc functions (ledcSetup, ledcAttachPin, ledcWrite) because it has a dedicated hardware PWM controller that is more powerful and stable than the simple analogWrite() found on basic Arduino boards. This provides reliable dimming without tying up the main processor.

Buy from:

Myduino AIoT Education Kit (click here) from Myduino.com