Use the GPIO pins of the ESP32

Discover all the relevant information on the ESP32 pinout on a single page to correctly use these GPIO pins for your DIY electronics project. Although there are many variations of ESP32 boards, the function of the pins remains the same. However, some pins may not be accessible, depending on your model.

There are plenty of ESP32 boards out there with different pin arrangements. Here is the detailed pin diagram of 2 various ESP32 boards. It will be beneficial for you to know the specific functions of each pin:

ESP32 WROOM Generic DevKit

Pinout of an ESP32 board
uPesy ESP32 WROOM DevKit

Pinout of the uPesy ESP32 Wroom DevKit board

Note

There is a significant difference between the 2 boards, which is not necessarily obvious: their widths . uPesy ESP32 boards can be put on a breadboard, and you can access pins on both sides, unlike most of the other ESP32 boards that are too “big” to be used easily on a breadboard …

Specific function of some ESP32 pins

The goal is to inform you of the limitations of some ESP32 GPIO pins to avoid having unpleasant surprises during your projects or having an incomprehensible bug in your program.

ESP32-based development boards typically have 33 pins except those for power. Some GPIO pins have a bit of a particular function:

If your ESP32 board has the pins GPIO6, GPIO7, GPIO8, GPIO9, GPIO10, GPIO11, you must not use them because they are connected to the ESP32 flash memory: if you use them on the ESP32 will not work.

pins used by the internal flash of the ESP32: do not connect them

Pins connected to the Flash memory of the ESP32
GPIO	Possible name
6	SCK / CLK
7	SDO / SD0
8	SDI / SD1
9	SHD / SD2
10	SWP / SD3
11	CSC / CMD

Note

For this reason that these pins are not available on the uPesy ESP32 boards.

The GPIO1 (TX0) and GPIO3 (RX0) pins communicate via USB in UART with the computer. If you use them, you will no longer upload programs to the board or use the serial monitor through the USB port. They can be helpful for programming the board without using USB with an external programmer. Fortunately, there are other UART interfaces available.
Pins GPIO36 (VP), GPIO39 (VN), GPIO34, GPIO35 can only be used as input. They also do not have built-in internal pullup and pulldown resistors (You cannot use pinMode (36, INPUT_PULLUP) or pinMode(36, INPUT_PULLDOWN) .
Some pins have a particular function when starting the ESP32. These are called Strapping Pins .

Strapping pins of the ESP32

They are used to put the ESP32 in BOOT mode (to run the program written to flash memory) or FLASH mode (to upload the program to flash memory). Depending on the voltage on these pins, the ESP32 will boot either in BOOT mode or in FLASH mode.

The strapping pins are the pins GPIO0, GPIO2, GPIO12 (MTDI) and GPIO15 (MTDO) .

You can use them, but you just have to be careful when setting a logic state (3.3V or 0V) with an external pullup or pulldown resistor.

Tip

If your ESP32 board works correctly, and then nothing works (can’t upload the code or launch it) when you add a sensor, it will likely be linked to these famous strapping pins.
When booting the ESP32, some pins quickly switch logic states (0V → 3.3V) during a short time. If a relay is attached to these pins, you may have some weird bugs that temporarily switch the relay. The faulty pins are:
- GPIO 1 : Send the ESP32 boot logs via the UART
- GPIO 3 : Voltage of 3.3V during boot
- GPIO 5 : Sends a PWM signal during boot
- GPIO 14 : Sends a PWM signal during boot
- GPIO 15 : Send the ESP32 boot logs via the UART
Note

You can, of course, use these pins. If you have a weird behavior when starting the ESP32 with one of these pins, you will probably have to choose another one.
The EN pin is used to activate or deactivate the ESP32 via an external wire. It is connected to the EN button on the board. When the ESP32 is on, it’s at 3.3V. If we put this pin to the ground, the ESP32 is switched off. You can use it when the ESP32 is in a box, and you want to turn it on/off with a switch.
On boards that use an ESP32-WROVER module to have more RAM (the uPesy ESP32 Wrover DevKit, for example), the pins GPIO16 and GPIO17 are not available because they are used internally by the PSRAM.
Others GPIO pins have no particular restrictions.

Summary of all ESP32 GPIO pins

Summary of all ESP32 GPIO pins
GPIO	INPUT	OUTPUT	Comments
0	YES (Internal pullup)	YES	Must be at 0V during FLASH
1 (TX0)	NO	YES	UART communication with the PC
2	YES (Internal pulldown)	YES	Must be at 0V during FLASH
3 (RX0)	YES	NO	UART communication with the PC
4	YES	YES
5	YES	YES
6	NO	NO	Connected to internal flash
7	NO	NO	Connected to internal flash
8	NO	NO	Connected to internal flash
9	NO	NO	Connected to internal flash
10	NO	NO	Connected to internal flash
11	NO	NO	Connected to internal flash
12 (MTDI)	YES (Internal pulldown)	YES	Must be at 0V during BOOT
13	YES	YES
14	YES	YES
15 (MTDO)	YES (Internal pullup)	YES	Startup log if at 3.3V.
16	YES	YES	Not available on WROVER
17	YES	YES	Not available on WROVER
18	YES	YES
19	YES	YES
21	YES	YES
22	YES	YES
23	YES	YES
25	YES	YES
26	YES	YES
27	YES	YES
32	YES	YES
33	YES	YES
34	YES	NO	No internal pullup/pulldown
35	YES	NO	No internal pullup/pulldown
36 (VP)	YES	NO	No internal pullup/pulldown
39 (VN)	YES	NO	No internal pullup/pulldown
EN	NO	NO	Connected to the EN button (ESP32 Reset)

ESP32 Peripherals

To interact with modules, sensors, or electronic circuits, the ESP32, like any microcontroller, has a multitude of peripherals. There are also many more than on a classic Arduino Uno board.

The ESP32 has the following peripherals:

3 UART interfaces
2 I2C interfaces
3 SPI interfaces
16 PWM outputs
10 capacitive sensors
18 analog inputs (ADC)
2 DAC outputs

Some peripherals are already used by the ESP32 during its essential operation. In reality, there are therefore fewer possible interfaces for each peripheral.

Tip

The ESP32 pins are much more modular than the Arduino: You can “attach” a UART, I2C, SPI, PWM peripheral to whatever pins you want. The SPI, I2C, UART, PWM, DAC are no longer associated with specific pins. For example, on the Arduino Uno, you could only have SPI on pins 10, 11, 12, 13. With the ESP32, you can choose which ones you want. Only the ADC and the capacitive sensors are assigned to fixed pins. ESP32 pinouts available on the Internet show the connection made by default (if we do not specify the pins used). It remains a good practice to use the pins by default to keep good compatibility with external libraries as long as this does not limit the connection of your wires.

UART on ESP32

UART is the serial protocol that allows data to be easily exchanged between 2 devices . The ESP32 has 3 UART buses: UART0, UART1, and UART2. They can be used to communicate with a sensor, an Arduino, a Raspberry Pi, a computer …

UART0 is by default on the pins GPIO1 (TX0) and GPIO3 (RX0) of the ESP32. It is used to communicate with the computer through the serial monitor. This is also the one that is used to flash the ESP32 board. Usually, it displays messages to the console when using Serial.println() .
To use UART2, just add Serial2.begin() in the setup() function and use the Serial2.println() to send messages. By default, the UART2 bus is on pins GPIO16 (RX2) and GPIO17 (TX2) , but they can be changed during setup (useful with an ESP32 Wrover module). This simple code allows you to use the UART2 bus:
```
void setup() {
  Serial2.begin(115200);

}

void loop() {
  Serial2.println("Hello from UART2");
  delay(100);
}
```
Note

Messages will not be displayed on the serial monitor since the UART2 is not routed to the USB of the computer.

Message sent via UART2 from pin GPIO17
UART1 is by default on the pins used by the ESP32 flash. However, you can use it thanks to the “ESP32 GPIO matrix” by choosing the pins you want. So this code makes it possible to have a serial link on pins GPIO14 and GPIO12 using the UART1 bus.
```
void setup() {
  /*
  * UART1  -> Serial1
  * RX Pin -> GPIO 14
  * TX Pin -> GPIO 12
  * UART Configuration -> SERIAL_8N1
  */
  Serial1.begin(115200,SERIAL_8N1,14,12);

}

void loop() {
  Serial1.println("Hello from UART1");
  delay(100);
}
```
Message sent via UART1 from pin GPIO12

The I2C on the ESP32

The ESP32 has 2 I2C buses :

The I2C0 bus is the one used by default by Arduino libraries. It is connected to the pins GPIO22 (SCL) and GPIO21 (SDA) of the ESP32. It can be used on any pin of the ESP32 when you use the Wire.h library by specifying the pins with the function Wire.begin (SDA_PIN, SCL_PIN) .

The I2C1 bus can also be used on any pin (pay attention to the limited pins described previously). Here is an example that uses the second I2C bus:

            #include <Wire.h>

TwoWire I2C1 = TwoWire(1);

void setup() {
  I2C1.begin(14,12,400000); // SDA pin 14, SCL pin 12, 400kHz frequency
}

void loop() {
  I2C1.beginTransmission(0x42);
  I2C1.write(140);
  I2C1.endTransmission();
  delay(100);
}

           

SPI on ESP32

Even though the ESP32 has 3 SPI buses, only 2 can be used because one is used by the internal flash memory. The 2 available SPI buses are called VSPI and HSPI.

Note

Arduino libraries that use the SPI use the VSPI bus by default.

By default, the pin mapping is as follows:

SPI	MOSI	MISO	SCK / CLK	CS / SS
VSPI	GPIO 23	GPIO 19	GPIO 18	GPIO 5
HSPI	GPIO 13	GPIO 12	GPIO 14	GPIO 15

As for the I2C, it is possible to manually choose the pins that we want to use for the SPI by specifying the pins on the initialization: SPI.begin (CLK_PIN, MISO_PIN, MOSI_PIN, SS_PIN);

PWM on the ESP32

The ESP32 has 16 channels that can be used to generate PWM signals: you can have up to 16 different PWM outputs. All pins that can be configured as a digital output can be used to output a PWM signal. The use of PWM is different from that on Arduino: we can configure more parameters. I suggest you check out using the PWM of ESP32 with Arduino code to use it in your projects.

Capacitive sensors on the ESP32

The ESP32 has 10 capacitive sensors (only 9 if the GPIO0 pin is not available). They can be used as tactile buttons. These are the recognized TOUCH pins seen on the ESP32 pinout. They can also be used when the ESP32 is in DeepSleep mode (power saving mode) to wake it up. I invite you to read the use capacitive sensors on the ESP32 with Arduino code for more details.

The internal capacitive sensors are connected to the following GPIO pins:

TOUCH0	TOUCH1	TOUCH2	TOUCH3	TOUCH4
GPIO 4	GPIO 0	GPIO 2	GPIO 15	GPIO 13
TOUCH5	TOUCH6	TOUCH7	TOUCH8	TOUCH9
GPIO 12	GPIO 14	GPIO 27	GPIO 33	GPIO 32

ADC on ESP32

The ESP32 has 2 separate ADC: the ADC1 with 8 channels and the ADC2 with 10 channels, for a total of 18 analog inputs. For example, there is on pin GPIO34, channel number 6 of ADC1 (ADC1_CH6) . However, there is much less available in practice because of the Wi-Fi.

Warning

The ADC2 cannot be used when Wi-Fi is enabled because the ESP32’s Wi-Fi uses it to operate.

Mapping for ADC1
ADC1_CH0	ADC1_CH1	ADC1_CH2	ADC1_CH3	ADC1_CH4	ADC1_CH5	ADC1_CH6	ADC1_CH7
GPIO 36	GPIO 37	GPIO 38	GPIO 39	GPIO 32	GPIO 33	GPIO 34	GPIO 35

Mapping for ADC2 (rarely used)
ADC2_CH0	ADC2_CH1	ADC2_CH2	ADC2_CH3	ADC2_CH4
GPIO 4	GPIO 0	GPIO 2	GPIO 15	GPIO 13
ADC2_CH5	ADC2_CH6	ADC2_CH7	ADC2_CH8	ADC2_CH9
GPIO 12	GPIO 14	GPIO 27	GPIO 25	GPIO 26

In general, the ESP32 ADC is not very reliable despite its 12-bit resolution. I suggest you consult for more information on this, the article use and limits of ADC of ESP32 .

DAC on the ESP32

The ESP32 has two 8-bit DAC outputs to convert a digital signal into an analog signal (generating a sine, for example). The pins used are as follows:

DAC1	DAC2
GPIO 25	GPIO 26

Note

The resolution of only 8 bits of the DAC is insufficient for audio applications without quality deterioration. It is better to use an external DAC with a better resolution (12-24 bits) and use the I2S bus of the ESP32.

Use the GPIO pins of the ESP32

Specific function of some ESP32 pins

Summary of all ESP32 GPIO pins

ESP32 Peripherals

UART on ESP32

The I2C on the ESP32

SPI on ESP32

PWM on the ESP32

Capacitive sensors on the ESP32

ADC on ESP32

DAC on the ESP32

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