5.8 Turn the Knob

A potentiometer is a three-terminal device that is commonly used to adjust the resistance in a circuit. It features a knob or a sliding lever that can be used to vary the resistance value of the potentiometer. In this project, we will utilize it to control the brightness of an LED, similar to a desk lamp in our daily life. By adjusting the position of the potentiometer, we can change the resistance in the circuit, thereby regulating the current flowing through the LED and adjusting its brightness accordingly. This allows us to create a customizable and adjustable lighting experience, similar to that of a desk lamp.

Required Components

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
ESP32 Starter Kit	320+	ESP32 Starter Kit

You can also buy them separately from the links below.

COMPONENT INTRODUCTION	PURCHASE LINK
ESP32 WROOM 32E	BUY
ESP32 Camera Extension	-
Breadboard	BUY
Jumper Wires	BUY
Resistor	BUY
LED	BUY
Potentiometer	BUY

Available Pins

• Available Pins

  Here is a list of available pins on the ESP32 board for this project.

  Available Pins

  IO14, IO25, I35, I34, I39, I36

• Strapping Pins

  The following pins are strapping pins, which affect the startup process of the ESP32 during power on or reset. However, once the ESP32 is booted up successfully, they can be used as regular pins.

  Strapping Pins

  IO0, IO12

Schematic

When you rotate the potentiometer, the value of I35 will change. By programming, you can use the value of I35 to control the brightness of the LED. Therefore, as you rotate the potentiometer, the brightness of the LED will also change accordingly.

Wiring

Code

Note

• You can open the file 5.8_pot.ino under the path of esp32-starter-kit-main\c\codes\5.8_pot.

• After selecting the board (ESP32 Dev Module) and the appropriate port, click the Upload button.

• Always displaying “Unknown COMxx”?

After the code is uploaded successfully, rotate the potentiometer and you will see the brightness of the LED change accordingly. At the same time you can see the analog and voltage values of the potentiometer in the serial monitor.

How it works?

1. Define constants for pin connections and PWM settings.

   const int potPin = 14; // Potentiometer connected to GPIO14
   const int ledPin = 26; // LED connected to GPIO26
   
   // PWM settings
   const int freq = 5000; // PWM frequency
   const int resolution = 12; // PWM resolution (bits)
   const int channel = 0; // PWM channel
   

   Here the PWM resolution is set to 12 bits and the range is 0-4095.

2. Configure the system in the setup() function.

   void setup() {
       Serial.begin(115200);
   
       // Configure PWM
       ledcSetup(channel, freq, resolution);
       ledcAttachPin(ledPin, channel);
   }
   

   • In the setup() function, the Serial communication is started at a baud rate of 115200.

   • The ledcSetup() function is called to set up the PWM channel with the specified frequency and resolution, and the ledcAttachPin() function is called to associate the specified LED pin with the PWM channel.

3. Main loop (executed repeatedly) in the loop() function.

   void loop() {
   
       int potValue = analogRead(potPin); // read the value of the potentiometer
       uint32_t voltage_mV = analogReadMilliVolts(potPin); // Read the voltage in millivolts
   
       ledcWrite(channel, potValue);
   
       Serial.print("Potentiometer Value: ");
       Serial.print(potValue);
       Serial.print(", Voltage: ");
       Serial.print(voltage_mV / 1000.0); // Convert millivolts to volts
       Serial.println(" V");
   
       delay(100);
   }
   

   • uint32_t analogReadMilliVolts(uint8_t pin);: This function is used to get ADC value for a given pin/ADC channel in millivolts.

     • pin GPIO pin to read analog value.

   The potentiometer value is directly used as the PWM duty cycle for controlling the LED brightness via the ledcWrite() function, as the range of values is also from 0 to 4095.