ESP32 UNO - Potentiometer
Want to read a knob position with the ESP32 Uno? Connect a potentiometer to the ESP32 Uno form board and turn the knob into a live 0-4095 number in the Serial Monitor. A potentiometer (also called a rotary angle sensor or variable resistor) is the simplest way to add a manual control to any Arduino IDE project.
By the end, you can:
- Connect a potentiometer to the board in three wires
- Read the analog value with analogRead()
- Convert the value into a voltage, an angle or a PWM level
- Understand why the ESP32 Uno needs 3.3V and a 12-bit range
Hardware Preparation
Or you can buy the following kits:
| 1 | × | DIYables Sensor Kit (18 sensors/displays) |
Additionally, some of these links are for products from our own brand, DIYables .
Overview of Potentiometer
By the end of this part, you know what the three pins do and how the knob makes a voltage.
You use a potentiometer to change a setting by hand. Typical jobs are the volume of a stereo, the brightness of a lamp or the zoom of an oscilloscope.
Pinout
A potentiometer has three pins.
| Pin | Connect To |
|---|---|
| GND | GND (0V) |
| VCC | The power rail of your board (use 3.3V on the ESP32 Uno) |
| Output (middle) | An analog input pin of the ESP32 Uno |
※ NOTE THAT:
You may swap the GND and VCC wires. The knob then works in the other direction.
How It Works
By the end of this part, you can predict the output voltage for any knob angle.
Inside the part, a sliding contact moves along a resistor track when you turn the shaft. The shaft starts at 0° (closest to the GND pin) and ends at a maximum angle named ANGLE_MAX (closest to the VCC pin). The output voltage follows the angle in a straight line.
| Shaft Angle | Output Voltage |
|---|---|
| 0° | 0V |
| Between 0° and ANGLE_MAX | angle × VCC / ANGLE_MAX |
| ANGLE_MAX | Same as VCC |
※ NOTE THAT:
Each maker picks its own ANGLE_MAX. You only need this number when you want to calculate the real rotation angle.
ESP32 Uno and the Analog Input
By the end of this part, you know what number the board gives you.
The ADC of the ESP32 Uno has 12 bits. It changes a voltage between 0V and about 3.3V into a whole number between 0 and 4095. This number is the ADC value. It is not an angle and not a voltage, so your code must convert it.
Good to know: the ESP32 Uno pins work at 3.3V and are NOT 5V tolerant. Power the potentiometer from 3.3V, so the output never goes higher.
Use Cases
- Convert the ADC value to the shaft angle
- Convert the ADC value to a voltage
- Convert the ADC value to a control value such as stereo volume, LED brightness or motor speed (the most common use)
Rescale Range
| FROM | TO | |||
|---|---|---|---|---|
| Angle | turned by you | 0° | → | ANGLE_MAX |
| Voltage | at the potentiometer output | 0V | → | 3.3V |
| ADC value | read by the ESP32 Uno | 0 | → | 4095 |
| Other value | calculated in code | VALUE_MIN | → | VALUE_MAX |
ESP32 Uno Pinout
Every Uno header pin of the ESP32 Uno form board has its own GPIO number, and your code uses that number. Match the labels in the diagram before you connect a wire.
Wiring Diagram
By the end of this part, the potentiometer is connected and ready for the sketch.
This image is created using Fritzing. Click to enlarge image
| Potentiometer Pin | ESP32 Uno Pin |
|---|---|
| VCC | 3.3V |
| GND | GND |
| Output | A0 (GPIO2) |
Good to know: the code reads this pin with the number 2, because A0 is GPIO2 on the ESP32 Uno.
WARNING
A0 (GPIO2) is a boot strapping pin. The chip checks it at start-up, so a module that pulls it the wrong way can stop the board from booting or uploading. A potentiometer is fine because its output sits between 0V and 3.3V, but unplug the output wire if an upload ever fails.
WARNING
Do not connect the potentiometer VCC to 5V. The output could reach 5V and damage the GPIO2 pin.
How To Program For Potentiometer
By the end of this part, you know the five lines that handle every potentiometer project.
Step 1 — Read the pin
Use analogRead() on the pin that holds the output wire. A0 is GPIO2.
Step 2 — Convert to an angle
The map() function rescales the number.
Step 3 — Convert to a voltage
Step 4 — Convert to a control value
Use any range you like, for example volume, brightness or motor speed.
Step 5 — Example with LED brightness
PWM brightness runs from 0 (off) to 255 (full). Map the knob onto this range:
※ NOTE THAT:
map() only gives whole numbers (int or long). When you need decimals, for example a voltage, use the floatMap() function below.
The floatMap() function:
ESP32 Uno Code
This sketch reads the knob once per second and prints the raw value and the voltage (0 to 3.3V).
| Code Part | What It Does |
|---|---|
| floatMap() | Rescales a decimal number from one range to another |
| analogSetAttenuation(ADC_11db) | Opens the ADC input range up to about 3.3V |
| analogRead(2) | Reads GPIO2 (A0) as a number from 0 to 4095 |
| floatMap(adc_value, 0, 4095, 0, 3.3) | Turns the number into a voltage |
| delay(1000) | Gives one reading per second |
The Serial Monitor now shows a new line every second.
Good to know: analogSetAttenuation(ADC_11db) lets the ESP32 Uno analog pin read the full range, from 0V up to about 3.3V. Without a wide range, the readings hit 4095 too early and the values look wrong.
Upload and Test
By the end of this part, the knob values appear on your screen.
- First time with this board? Set it up with ESP32 Uno - Getting Started before you continue.
- Build the circuit by following the wiring table above.
- Plug in the USB Type-C cable between the ESP32 Uno and your computer.
- Select the board in Arduino IDE: pick ESP32 Dev Module and the COM port of the board (CH340).
- Copy the code above and open it in Arduino IDE.
- Click the Upload button to send the code to the board.
- Open the Serial Monitor and set 9600 baud.
- Turn the knob slowly from one end to the other.
- Read the result in the Serial Monitor.
- Pro tip: the last digits can flicker a little even when the knob is still. Print the average of 8 reads if you need a calm number.
Video Tutorial
See the ESP32 Uno build in action in the video below.
ESP32 Uno vs UNO R4 for This Project
By the end of this part, you know what to change when you move this project from the UNO R4 to the ESP32 Uno.
| Item | Arduino UNO R4 | ESP32 Uno |
|---|---|---|
| Logic voltage | 5V | 3.3V |
| Potentiometer VCC | 5V or 3.3V | 3.3V only |
| Analog pin used | A0 | A0 (GPIO2), written as 2 in code |
| ADC range | 0 to 1023 | 0 to 4095 |
| Extra code line | none | analogSetAttenuation(ADC_11db) |
| Voltage math | 0 to 5V | 0 to 3.3V |
| Arduino IDE board | Arduino UNO R4 WiFi | ESP32 Dev Module |
The wiring stays on the same A0 header position. Only the power wire moves to 3.3V, and the numbers in your math change.
Go Wireless: Show the Knob Value on Your Phone
By the end of this part, you have an idea to read the potentiometer without a cable.
The ESP32 Uno has WiFi and Bluetooth, so the knob value does not have to stay in the Serial Monitor. Send the number to a web page or to a phone app and watch a gauge or a graph move while you turn the knob. Remember that A0 (GPIO2) is an ADC2 pin, which cannot be read while WiFi is on. For a WiFi version, use A2 (GPIO35) for the output wire and change the code to analogRead(35).
Try These Next
- Dim an LED with the knob: map the ADC value to 0-255 and use PWM
- Print the shaft angle in degrees with map()
- Control a servo with the knob, see the ESP32 Uno - Potentiometer Servo Motor tutorial
- Average 8 readings to get a very stable value
Function References
Troubleshooting
| Problem | Possible Cause | Solution |
|---|---|---|
| No COM port in Arduino IDE | CH340 driver missing or a charge-only cable | Install the CH340 driver and use a USB cable that carries data |
| Upload fails with Failed to connect or Waiting for download | Board is not in download mode | Hold the BOOT button while the upload starts |
| Board does not boot or upload with the knob connected | A0 (GPIO2) is a boot strapping pin and was pulled the wrong way | Unplug the output wire while uploading, or move to A2 (GPIO35) and change the code |
| Value stays at 0 | VCC wire missing or the output wire is on the wrong pin | Check the 3.3V, GND and A0 wires |
| Value reaches 4095 before the knob ends | ADC range not widened | Keep analogSetAttenuation(ADC_11db) in setup() |
| Value jumps around | Loose breadboard contact or ADC noise | Press the wires in firmly and average several reads |
| Value goes down when you turn up | VCC and GND wires are swapped | Swap the two outer wires |
| Voltage shows above 3.3V | Code still uses 1023 or 5V from older 10-bit 5V sketches | Use 4095 and 3.3 in map() and floatMap() |
| Nothing in the Serial Monitor | Wrong baud rate | Set the Serial Monitor to 9600 |
| analogRead stuck while WiFi is on | A0 (GPIO2) is an ADC2 pin | Use A2 (GPIO35) or GPIO32 or GPIO33 |
FAQ
How does a potentiometer make a changing voltage?
It is a resistor track with a sliding contact. When you turn the shaft, the contact moves, and the middle pin gives a share of the supply voltage that depends on the angle.
Can I power the potentiometer from 5V on the ESP32 Uno?
No. The output could reach 5V, and the ESP32 Uno pins are not 5V tolerant. Use the 3.3V pin.
What value range does analogRead() give on the ESP32 Uno?
It gives 0 to 4095, because the ADC has 12 bits. The UNO R4 sketch uses 0 to 1023 by default, so change the numbers in map() when you copy old code.
Why does the code call analogSetAttenuation(ADC_11db)?
It sets the ESP32 Uno ADC input range to about 0-3.3V, so the full sensor signal maps to 0-4095. With a smaller range, readings saturate early. The UNO R4 does not need this line, it is ESP32-only. Keep the sensor output at 3.3V or less.
Which resistance value should I buy?
A 10kΩ linear potentiometer is a good choice. Smaller values waste a little more current, and larger values pick up more noise.
How do I get an angle instead of a voltage?
Use map(adc_value, 0, 4095, 0, ANGLE_MAX). Take ANGLE_MAX from the datasheet of your part, often around 270°.
Can I use A1 to A5 for the knob?
Yes. All six analog header pins can read it. A2 to A5 (GPIO35, 34, 36, 39) are input only, which is perfect for a sensor. A0 and A1 (GPIO2, GPIO4) are ADC2 pins that fail while WiFi is on.
Can I read two potentiometers at once?
Yes. Wire the second output to another analog pin, call analogRead() with its GPIO number, and keep one analogSetAttenuation(ADC_11db) line in setup().
Can I show the knob value on a web page with the ESP32 Uno?
Yes, the ESP32 Uno has WiFi and Bluetooth. See the Go Wireless section for ready tutorials. Use an ADC1 pin such as A2 (GPIO35) for WiFi projects.
What if my project needs more pins than the Uno headers give?
The ESP32 Uno has a few extra holes near the power header: GPIO32 and GPIO33 (I/O, PWM, analog on ADC1, so they also work while WiFi is on) and GPIO15 (I/O, PWM, analog on ADC2). Solder pin headers to use them and write the GPIO number in code. For more potentiometers in a WiFi project, GPIO32 and GPIO33 fit best. Two warnings: (1) GPIO15 and GPIO0 (the IO0 pin at the unused Uno NC position) are boot strapping pins, and a wrong connection can stop the board from booting or uploading code, so use GPIO32 and GPIO33 first. (2) Never use the six holes under the digital header (SD0-SD3, CMD, CLK = GPIO6-GPIO11), because they are wired to the flash chip and using them crashes the board.