I will refer to the 30 pin as ESP32-30 in order to differentiate between the 30 and 38 pin version.

ESP32-30 Pinout Reference


Tutorial-for-ESP32-Pinout-Reference



One of the great things about ESP32-30 is that it has a lot more GPIOs than ESP8266.
You won’t have to juggle or multiplex your IO pins. There are a few things to 
watch out for so please read the pinout carefully.

Note:
Please note that the following pinout reference is for the popular ESP32-30 devkit
v1 development board with 30 pins.


30pin esp32 dev board

Not all pins are broken out in all ESP32-30 development boards, but each specific 
pin works the same way regardless of the development board you are using.



 ESP32-30 Peripherals and I/O

Although the ESP32-30 has total 48 GPIO pins, only 25 of them are broken out to 
the pin headers on both sides of the development board. These pins can be 
assigned to all sorts of peripheral duties, including:




15 ADC channels 
15 channels of 12-bit SAR ADC’s. The ADC range can 
be set, in firmware, to either 0-1V, 0-1.4V, 0-2V, or 0-4V
2 UART interfaces
2 UART interfaces. One is used to load code 
serially.  They feature flow control, and support IrDA too!
25 PWM outputs
25 channels of PWM pins for dimming LEDs or 
controlling motors.
2 DAC channels
8-bit DACs to produce true analog voltages.
3 SPI & 1 I2C interfaces
There are 3 SPI and 1 I2C interfaces to 
hook up all sorts of sensors and peripherals.
9 Touch Pads
9 GPIOs feature capacitive touch sensing.



Thanks to the ESP32-30’s pin multiplexing feature (Multiple peripherals multiplexed
on a single GPIO pin). Meaning a single GPIO pin can act as an ADC input/DAC 
output/Touch pad.

You can get extensive information about ESP32-30 from the datasheet.
 ESP32-30 Datasheet 

ESP32-30 Pinout

The ESP32-30 development board has a total of 30 pins that connect it to the 
outside world. For simplicity, pins with similar functionality are grouped 
together. The pinout is as follows:


esp32 pinout

Let us analyze the ESP32-30 pins and their functions one by one in more detail.



GPIO Pins

ESP32-30 development board has 25 GPIO pins which can be assigned to various 
functions programmatically. Each digital enabled GPIO can be configured to 
internal pull-up or pull-down, or set to high impedance.


esp32 gpio pins



Which ESP32-30 GPIOs are safe to use?

Because the ESP32-30 has many pins with specific functions, they may not be 
suitable for your projects. The following table shows which pins are safe to 
use and which pins require more attention before using them.

🟢 ✓    – Your first priority pins. They are perfectly fine to use.
🟠 ! – Pay attention as their behavior can be unpredictable, mainly during boot.
         Don’t use them unless you absolutely need to.
⭕ X -  It is not recommended to use these pins. So avoid them.


Label
GPIO
Safe to use?
Reason
D0
0
🟠 !
must be HIGH during boot and LOW for programming
TX0
1
⭕ X
Tx pin, used for flashing and debugging
D2
2
🟠 !
must be LOW during boot and also connected to the on-board LED
RX0
3
⭕ X
Rx pin, used for flashing and debugging
D4
4
🟢 ✓
D5
5
🟠 !
must be HIGH during boot
D6
6
⭕ X
Connected to Flash memory
D7
7
⭕ X
Connected to Flash memory
D8
8
⭕ X
Connected to Flash memory
D9
9
⭕ X
Connected to Flash memory
D10
10
⭕ X
Connected to Flash memory
D11
11
⭕ X
Connected to Flash memory
D12
12
must be LOW during boot
D13
13
🟢 ✓

D14
14
🟢 ✓

D15
15
🟠 !
must be HIGH during boot, prevents startup log if pulled LOW
RX2
16
🟢 ✓

TX2
17
🟢 ✓

D18
18
🟢 ✓

D19
19
🟢 ✓

D21
21
🟢 ✓

D22
22
🟢 ✓

D23
23
🟢 ✓

D25
25
🟢 ✓

D26
26
🟢 ✓

D27
27
🟢 ✓

D32
32
🟢 ✓

D33
33
🟢 ✓

D34
34
🟠 !
Input only GPIO, cannot be configured as output
D35
35
🟠 !
Input only GPIO, cannot be configured as output
VP
36
🟠 !
Input only GPIO, cannot be configured as output
VN
39
🟠 !
Input only GPIO, cannot be configured as output


For your convenience, here is an image showing which GPIO pins are safe to use.


esp32 gpio pins that are safe to use



Input Only GPIOs

Pins GPIO34, GPIO35, GPIO36(VP) and GPIO39(VN) cannot be configured as outputs,
they can be used as either digital inputs, analog inputs, or for other unique 
purposes. Also note that they do not have internal pull-up or pull-down 
resistors, like the other GPIO pins.

Also pins GPIO36(VP) and GPIO39(VN) are an integral part of the ultra-low-noise
pre-amplifier for the ADC, which help to configure the sampling time and noise 
of the pre-amp.



ESP32-30 Interrupt Pins

All GPIOs can be configured as interrupts.



ADC Pins

The ESP32-30 has fifteen 12-bit ADC input channels. These are GPIOs that can be 
used to convert the analog voltage on the pin to a digital number.


esp32 adc pins

The ADC on the ESP32-30 is a 12-bit ADC meaning it has the ability to detect 4096 
(212) discrete analog levels. In other words, it will map input voltages between
0 and the operating voltage 3.3V into integer values between 0 and 4095. For 
example, this yields a resolution between readings of: 3.3 volts / 4096 units 
or, 0.0008 volts (0.8 mV) per unit.

You also have the ability to set the ADC resolution and ADC range of your 
channels in code.

Warning:
The ADC2 pins cannot be used when Wi-Fi is enabled. If your project requires 
Wi-Fi, consider using the ADC1 pins instead.



DAC Pins

The ESP32-30 features two 8-bit DAC channels that can be used to convert digital 
signals into true analog voltages. It can be used as a “digital potentiometer” 
to control analog devices.


esp32 dac pins

This dual-DAC on the ESP32-30 has 8-bit resolution, which means that values between
0 and 256 will produce an analog voltage somewhere between 0 and 3.3V.



Touch Pins

ESP32-30 has 9 capacitive touch-sensing GPIOs. When a capacitive load (such as a 
human finger) is in close proximity to the GPIO, the ESP32-30 detects the change 
in capacitance.


esp32 touch pins

These pins can be easily turned into a touchpad by connecting them to any 
conductive object such as wire, thread, foil, cloth, conductive paint, etc. The
low-noise nature of the design and the high sensitivity of the circuit allow 
relatively small pads to be used.

These capacitive touch pins can also be used to wake the ESP32-30 from deep sleep.



SPI Pins

SPI Pins ESP32-30 features three SPIs (SPI, HSPI and VSPI) in slave and master 
modes. These SPIs also support the following general-purpose SPI features:


    4 timing modes of the SPI format transfer
    Up to 80 MHz and the divided clocks of 80 MHz
    Up to 64-Byte FIFO



esp32 spi pins

Only VSPI and HSPI are usable SPI interfaces and the third SPI bus is used by 
the integrated flash memory chip. Standard libraries usually use VSPI pins 
between the two.


HSPI vs. VSPI
Sometimes HSPI is misinterpreted as “Hardware” SPI and VSPI as “Virtual” or 
“Software” SPI. Although in reality they all work the same way!




I2C Pins

The ESP32-30 has a single I2C bus that allows you to connect up to 112 sensors and
peripherals. The SDA and SCL pins are, by default, assigned to the following 
pins. However, you can bit-bang the I2C protocol on any GPIO pins with 
wire.begin(SDA, SCL) command.


esp32 i2c pins



UART Pins

ESP32-30 has 2 UART interfaces, i.e. UART0 and UART2, which provide asynchronous 
communication (RS232 and RS485) and IrDA support, and communicate at up to 5 
Mbps.

    UART0 pins are connected to the USB-to-Serial converter and are used for 
flashing and debugging. Therefore it is not recommended to use the UART0 pins.
    UART2, on the other hand, are additional Serial1 pins, and are not connected
to the USB-to-Serial converter. This means that you can use them to connect to 
UART-devices such as GPS, fingerprint sensor, etc.


esp32 uart pins



PWM Pins

The board has 25 channels (Nearly All GPIO pins) of PWM pins controlled by Pulse
 Width Modulation (PWM) controller. The PWM output can be used for driving 
digital motors and LEDs.


esp32 pwm pins

The controller consists of PWM timers and the PWM operator. Each timer provides timing in synchronous or independent form, and each PWM operator generates the 
waveform for one PWM channel.



RTC GPIO Pins

Some GPIOs are routed to the RTC low-power subsystem, they are called RTC GPIOs.
These are special pins that are used to wake the ESP32-30 from deep sleep when the
Ultra Low Power (ULP) co-processor is running. The following GPIOs can be used 
as external wake up sources.


esp32 rtc gpio pins



Power Pins

There are two power pins viz. VIN pin & 3.3V pin. The VIN pin can be used to 
directly supply the ESP32-30 and its peripherals, if you have a regulated 5V 
voltage source. The 3.3V pin is the output of an on-board voltage regulator. 
This pin can be used to supply power to external components. GND is a ground 
pin of ESP32-30 development board.


esp32 power pins



Enable Pin

EN Pin is used to enable ESP32-30. The chip is enabled when pulled HIGH. When 
pulled LOW the chip works at minimum power.