ESP32 Pinout Reference: GPIO, ADC, PWM & Communication

Meta:Complete ESP32 Pinout Reference covering GPIO, ADC, DAC, PWM, and communication interfaces. Includes safe pin recommendations, strapping pins, and wiring tips.

The ESP32 Pinout Reference is essential knowledge for anyone serious about building reliable embedded projects. After years of designing PCBs with this chip, I’ve learned that understanding which pins to use—and which to avoid—can mean the difference between a project that works flawlessly and one that frustrates endlessly.

This guide provides a complete reference for ESP32 GPIO pins, covering analog-to-digital conversion, PWM generation, and all communication interfaces. Whether you’re transitioning from Arduino boards or diving straight into ESP32 development, this pinout reference will help you make informed design decisions.

Understanding ESP32 GPIO Architecture

The ESP32 microcontroller features 48 GPIO pins total, though typical development boards expose only 25-36 of these. What makes the ESP32 remarkable is its GPIO matrix—a flexible routing system that allows most peripheral functions to be assigned to almost any pin through software configuration.

Unlike traditional microcontrollers where SPI must use specific pins, the ESP32 lets you route SPI, I2C, UART, and PWM signals to your preferred GPIO pins. This flexibility simplifies PCB routing and allows creative solutions when pins conflict.

However, this flexibility comes with important caveats. Some pins have specific boot-time requirements. Others connect to internal flash memory and cannot be used. Understanding these restrictions separates successful ESP32 designs from problematic ones.

ESP32 DevKit V1 Pin Categories

Category	Pin Count	Description
General Purpose GPIO	25	Available for digital I/O
Input-Only GPIO	4	GPIO34-39, cannot output
ADC Channels	18	Analog input measurement
DAC Channels	2	Analog voltage output
Touch Sensors	10	Capacitive touch detection
PWM Channels	16	Pulse width modulation
Strapping Pins	5	Affect boot behavior

Complete ESP32 Pinout Reference Table

This comprehensive table covers the 30-pin ESP32 DevKit V1, one of the most common development boards. Pin behavior remains consistent across different manufacturers, though physical layouts vary.

Full GPIO Pin Mapping

GPIO	Board Pin	ADC	Touch	Default Function	Safe to Use
GPIO0	D0	ADC2_CH1	T1	Boot mode select	⚠️ Caution
GPIO1	TX0	–	–	UART0 TX	⚠️ Serial
GPIO2	D2	ADC2_CH2	T2	Boot mode, LED	⚠️ Caution
GPIO3	RX0	–	–	UART0 RX	⚠️ Serial
GPIO4	D4	ADC2_CH0	T0	General I/O	✅ Safe
GPIO5	D5	–	–	VSPI CS0	⚠️ Strapping
GPIO12	D12	ADC2_CH5	T5	HSPI MISO	⚠️ Strapping
GPIO13	D13	ADC2_CH4	T4	HSPI MOSI	✅ Safe
GPIO14	D14	ADC2_CH6	T6	HSPI CLK	✅ Safe
GPIO15	D15	ADC2_CH3	T3	HSPI CS0	⚠️ Strapping
GPIO16	D16	–	–	UART2 RX	✅ Safe
GPIO17	D17	–	–	UART2 TX	✅ Safe
GPIO18	D18	–	–	VSPI CLK	✅ Safe
GPIO19	D19	–	–	VSPI MISO	✅ Safe
GPIO21	D21	–	–	I2C SDA	✅ Safe
GPIO22	D22	–	–	I2C SCL	✅ Safe
GPIO23	D23	–	–	VSPI MOSI	✅ Safe
GPIO25	D25	ADC2_CH8	–	DAC1	✅ Safe
GPIO26	D26	ADC2_CH9	–	DAC2	✅ Safe
GPIO27	D27	ADC2_CH7	T7	General I/O	✅ Safe
GPIO32	D32	ADC1_CH4	T9	General I/O	✅ Safe
GPIO33	D33	ADC1_CH5	T8	General I/O	✅ Safe
GPIO34	D34	ADC1_CH6	–	Input only	✅ Input
GPIO35	D35	ADC1_CH7	–	Input only	✅ Input
GPIO36	VP	ADC1_CH0	–	Input only	✅ Input
GPIO39	VN	ADC1_CH3	–	Input only	✅ Input

Pins to Avoid

GPIO	Reason	Notes
GPIO6-11	SPI Flash	Connected to internal flash memory
GPIO0	Boot mode	Must be HIGH for normal boot
GPIO2	Boot mode	Should be LOW or floating at boot
GPIO12	Flash voltage	HIGH at boot causes boot failure
GPIO15	Debug output	Outputs debug data at boot

ESP32 ADC Pinout Reference

The ESP32 features two 12-bit SAR (Successive Approximation Register) ADCs with 18 channels total. This provides excellent analog measurement capability, but several important limitations affect real-world usage.

ADC Channel Distribution

ADC Unit	Channels	GPIO Pins	WiFi Compatible
ADC1	8	32, 33, 34, 35, 36, 37, 38, 39	✅ Yes
ADC2	10	0, 2, 4, 12, 13, 14, 15, 25, 26, 27	❌ No

ADC1 Pin Details (WiFi Safe)

Channel	GPIO	Available on DevKit	Notes
ADC1_CH0	GPIO36	Yes	Input only, VP pin
ADC1_CH3	GPIO39	Yes	Input only, VN pin
ADC1_CH4	GPIO32	Yes	General purpose
ADC1_CH5	GPIO33	Yes	General purpose
ADC1_CH6	GPIO34	Yes	Input only
ADC1_CH7	GPIO35	Yes	Input only

Critical ADC Limitations

The most important restriction: ADC2 cannot be used while WiFi is active. The WiFi driver exclusively claims ADC2 hardware, making those pins unavailable for analog readings during wireless operation.

For any project using WiFi, plan your analog sensors exclusively on ADC1 pins (GPIO32-39). This single design decision eliminates countless hours of debugging mysterious ADC failures.

The ESP32 ADC also exhibits non-linearity at voltage extremes. Readings below 100mV and above 3.2V become unreliable. For precision measurements, consider external ADCs or implement calibration routines using the ESP32’s eFuse calibration data.

ADC Resolution and Attenuation

Attenuation	Voltage Range	Use Case
0 dB	0 – 1.1V	Precision low-voltage
2.5 dB	0 – 1.5V	Extended range
6 dB	0 – 2.2V	Medium range
11 dB	0 – 3.3V	Full range (default)

ESP32 DAC Pinout Reference

The ESP32 includes two 8-bit Digital-to-Analog Converter channels for generating true analog voltage outputs. While limited in resolution, these DAC channels prove useful for many applications.

DAC Channel Assignment

Channel	GPIO	Voltage Range	Resolution
DAC1	GPIO25	0 – 3.3V	8-bit (256 levels)
DAC2	GPIO26	0 – 3.3V	8-bit (256 levels)

DAC applications include generating reference voltages, simple audio output, analog control signals, and creating waveforms for testing purposes. The 8-bit resolution limits audio quality, but works acceptably for basic tones and alerts.

For high-fidelity audio applications, use an external I2S DAC. The ESP32’s I2S interface supports professional audio DACs with 24-bit resolution and sample rates exceeding 192kHz.

ESP32 PWM Pinout Reference

The ESP32’s LED Control (LEDC) peripheral provides 16 independent PWM channels with impressive flexibility. Unlike some microcontrollers that dedicate specific pins to PWM, the ESP32 can generate PWM on any output-capable GPIO.

PWM Channel Specifications

Feature	Specification
Total Channels	16
Independent Frequencies	8 (shared pairs)
Resolution	1-16 bits configurable
Maximum Frequency	40 MHz (at 1-bit)
Typical Frequency	5 kHz (at 13-bit)

PWM-Capable GPIO Pins

All GPIO pins capable of output can generate PWM signals. This excludes only the input-only pins (GPIO34-39). In practice, avoid using strapping pins and serial pins for PWM unless absolutely necessary.

Recommended PWM pins: GPIO4, GPIO13, GPIO14, GPIO16, GPIO17, GPIO18, GPIO19, GPIO21, GPIO22, GPIO23, GPIO25, GPIO26, GPIO27, GPIO32, GPIO33

PWM Configuration Example

// ESP32 PWM Configuration

const int pwmChannel = 0;

const int pwmFrequency = 5000;

const int pwmResolution = 8;

const int pwmPin = 18;

void setup() {

  ledcSetup(pwmChannel, pwmFrequency, pwmResolution);

  ledcAttachPin(pwmPin, pwmChannel);

}

void loop() {

  ledcWrite(pwmChannel, 128);  // 50% duty cycle

}

ESP32 Communication Interface Pinout

The ESP32’s GPIO matrix enables remarkable flexibility in assigning communication peripherals to GPIO pins. While default pins exist for convenience, you can reassign most interfaces to alternative pins through software configuration.

I2C Interface Pins

The ESP32 supports two I2C bus interfaces, both configurable to any output-capable GPIO pins.

Interface	Default SDA	Default SCL	Max Speed
I2C0	GPIO21	GPIO22	400 kHz
I2C1	Configurable	Configurable	400 kHz

I2C works through software bit-banging on the ESP32, allowing any GPIO pin combination. The default pins (GPIO21 SDA, GPIO22 SCL) remain the most commonly used and best documented.

SPI Interface Pins

The ESP32 provides four SPI controllers, though only two are available for general use (SPI0 and SPI1 connect to internal flash).

Interface	MOSI	MISO	CLK	CS	Max Speed
HSPI	GPIO13	GPIO12	GPIO14	GPIO15	80 MHz
VSPI	GPIO23	GPIO19	GPIO18	GPIO5	80 MHz

For maximum SPI performance (80 MHz), use the default pin assignments. Remapped pins pass through the GPIO matrix, limiting speeds to approximately 40 MHz.

UART Interface Pins

Three UART interfaces provide serial communication capability.

Interface	Default TX	Default RX	Notes
UART0	GPIO1	GPIO3	USB Serial, debugging
UART1	GPIO10	GPIO9	Flash pins, remap required
UART2	GPIO17	GPIO16	General use

UART0 connects to the USB-to-serial converter on most development boards. Reserve this for debugging and programming. UART1 defaults to pins used by the internal flash, requiring remapping before use. UART2 provides the cleanest option for connecting external serial devices.

Remapping UART1 Example

#include <HardwareSerial.h>

HardwareSerial MySerial(1);  // UART1

void setup() {

  MySerial.begin(9600, SERIAL_8N1, 26, 27);  // RX=26, TX=27

}

ESP32 Touch Sensor Pinout

The ESP32 integrates 10 capacitive touch sensors, enabling button-free user interfaces. These sensors detect proximity and touch through changes in pin capacitance.

Touch Sensor Pin Assignment

Touch	GPIO	ADC	Notes
T0	GPIO4	ADC2_CH0	Safe to use
T1	GPIO0	ADC2_CH1	Strapping pin
T2	GPIO2	ADC2_CH2	Strapping pin
T3	GPIO15	ADC2_CH3	Strapping pin
T4	GPIO13	ADC2_CH4	Safe to use
T5	GPIO12	ADC2_CH5	Strapping pin
T6	GPIO14	ADC2_CH6	Safe to use
T7	GPIO27	ADC2_CH7	Safe to use
T8	GPIO33	ADC1_CH5	Safe to use
T9	GPIO32	ADC1_CH4	Safe to use

Touch sensors T8 and T9 on GPIO32 and GPIO33 offer the best combination—they work with WiFi active (ADC1 pins) and have no boot-time restrictions.

ESP32 Strapping Pins Reference

Five GPIO pins determine ESP32 boot behavior. Incorrect states on these pins during power-up cause boot failures or unexpected operation modes.

Strapping Pin Requirements

GPIO	Required State	Effect if Wrong
GPIO0	HIGH	Enters download mode
GPIO2	LOW/Floating	Boot may fail
GPIO5	HIGH	SDIO timing issues
GPIO12	LOW	Boot failure (3.3V flash)
GPIO15	HIGH	Suppresses boot messages

Most development boards include circuitry ensuring correct strapping pin states. Problems arise when external circuits pull these pins to incorrect levels during power-up.

If you must use strapping pins, ensure your external circuits don’t override the required boot states. Adding series resistors (1K-10K) between the ESP32 and external devices often resolves conflicts.

Useful Resources and Downloads

Resource	Description	URL
ESP32 Datasheet	Official Espressif documentation	espressif.com/documentation
ESP32 Technical Reference	Detailed peripheral information	espressif.com
Arduino-ESP32 Core	GitHub repository	github.com/espressif/arduino-esp32
ESP-IDF Documentation	Official development framework	docs.espressif.com
Random Nerd Tutorials	ESP32 project tutorials	randomnerdtutorials.com
Last Minute Engineers	Detailed pinout guides	lastminuteengineers.com

Frequently Asked Questions

Which ESP32 GPIO pins are safe to use for any purpose?

GPIO4, GPIO13, GPIO14, GPIO16, GPIO17, GPIO18, GPIO19, GPIO21, GPIO22, GPIO23, GPIO25, GPIO26, GPIO27, GPIO32, and GPIO33 are generally safe for any application. These pins have no special boot requirements and don’t conflict with internal peripherals. GPIO34-39 are safe but limited to input-only operation.

Can I use ADC2 pins while WiFi is enabled?

No. The WiFi driver exclusively controls ADC2 hardware during wireless operation. Any attempt to read ADC2 channels while WiFi is active returns unreliable results. Design your analog inputs around ADC1 pins (GPIO32-39) for projects requiring WiFi connectivity.

Why won’t my ESP32 boot when I connect a device to GPIO12?

GPIO12 is a strapping pin that determines flash voltage at boot. If GPIO12 reads HIGH during power-up, the ESP32 attempts to use 1.8V flash voltage, causing boot failure on boards with 3.3V flash. Ensure GPIO12 stays LOW during reset, or use a different pin for your device.

How many PWM outputs can the ESP32 generate simultaneously?

The ESP32 can generate 16 independent PWM outputs using the LEDC peripheral. However, only 8 different frequencies are available—channels share timers in pairs. For most applications requiring LED dimming, motor control, or servo signals, 16 channels with 8 frequencies provides ample flexibility.

What’s the maximum I2C or SPI speed on remapped pins?

SPI through the GPIO matrix (non-default pins) limits to approximately 40 MHz versus 80 MHz on default pins. I2C performance remains similar regardless of pin assignment since it uses software implementation. For maximum SPI throughput, stick with HSPI or VSPI default pins.

Conclusion

This ESP32 Pinout Reference covers the essential information needed for successful hardware design. The ESP32’s flexibility creates tremendous opportunities, but also demands careful pin selection to avoid boot conflicts and peripheral limitations.

Remember these key principles: use ADC1 pins for analog inputs with WiFi, respect strapping pin requirements, and leverage the GPIO matrix for routing flexibility. Document your pin assignments thoroughly—future you will appreciate the clarity.

The ESP32 remains one of the most capable and cost-effective microcontrollers available. Master its pinout, and you’ll build projects that work reliably from prototype through production.

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Suggested Meta Descriptions:

Option 1 (155 characters): Complete ESP32 Pinout Reference covering GPIO, ADC, DAC, PWM, and communication interfaces. Includes safe pin recommendations, strapping pins, and wiring tips.

Option 2 (152 characters): Master the ESP32 pinout with this detailed GPIO reference guide. Covers ADC channels, PWM configuration, I2C, SPI, UART pins, and boot mode requirements.

Option 3 (158 characters): ESP32 Pinout Reference for developers and engineers. Comprehensive guide to GPIO pins, analog inputs, PWM outputs, communication interfaces, and safe pin usage.