Esp32

• Frequency range: 1 Hz to 40 MHz
• Resolution: 1-16 bits (configurable)
• Recommended for PWM: 16, 17, 18, 19, 21, 22, 23, 25, 26, 27

Analog Input (ADC)

ADC1 (usable with WiFi): GPIO 32, 33, 34, 35, 36, 39

• 12-bit resolution (0-4095)
• 0-3.3V input range
• Attenuation configurable (0dB, 2.5dB, 6dB, 11dB)

ADC2 (CANNOT use when WiFi active): GPIO 0, 2, 4, 12, 13, 14, 15, 25, 26, 27

• Same specs as ADC1
• ⚠️ Critical: ADC2 is disabled when WiFi is running

Analog Output (DAC)

DAC Pins: GPIO 25, GPIO 26

• 8-bit resolution (0-255)
• 0-3.3V output range
• Use dacWrite(pin, value)

Interrupt-Capable Pins

All GPIO pins support interrupts

• Rising edge, falling edge, both edges, low level, high level
• Use attachInterrupt(digitalPinToInterrupt(pin), ISR, mode)

Communication Interfaces

UART (Serial)

UART0: RX=GPIO3, TX=GPIO1 (connected to USB)

• Default for Serial.println()
• Used by bootloader

UART1: RX=GPIO9, TX=GPIO10

• ⚠️ Connected to flash memory, not recommended for general use

UART2: RX=GPIO16, TX=GPIO17

• Recommended for external serial devices
• Can be remapped to other pins

I2C (Wire)

Default pins: SDA=GPIO21, SCL=GPIO22

• Can be remapped to any GPIO pair
• Master or slave mode
• Standard (100 kHz) and Fast (400 kHz) modes

SPI

VSPI (default):

• MOSI=GPIO23
• MISO=GPIO19
• SCK=GPIO18
• SS=GPIO5

HSPI:

• MOSI=GPIO13
• MISO=GPIO12
• SCK=GPIO14
• SS=GPIO15

Both can be remapped to other pins.

Pin Constraints and Special Functions

⚠️ Input-Only Pins

GPIO 34, 35, 36, 39 are INPUT ONLY

• No internal pull-up/pull-down resistors
• Cannot be used with pinMode(pin, OUTPUT)
• Cannot be used with pinMode(pin, INPUT_PULLUP)

⚠️ Strapping Pins (Boot Mode)

These pins affect boot mode and should be avoided for critical functions:

GPIO 0:

• Must be HIGH during boot
• Has internal pull-up
• Boot button usually connected here
• Safe to use after boot

GPIO 2:

• Must be LOW or floating during boot
• Has internal pull-down
• Some boards have built-in LED here

GPIO 5:

• Controls SDIO slave timing
• Has internal pull-up

GPIO 12:

• Controls flash voltage (VDD_SDIO)
• Must be LOW during boot for 3.3V flash
• Has internal pull-down

GPIO 15:

• Must be HIGH during boot
• Controls boot message output
• Has internal pull-up

Touch Sensing

Touch-capable pins: GPIO 0, 2, 4, 12, 13, 14, 15, 27, 32, 33

• Use touchRead(pin) to get capacitance value
• Threshold-based touch detection

RTC GPIO (Deep Sleep Wake)

RTC_GPIO pins: 0, 2, 4, 12-15, 25-27, 32-39

• Can wake ESP32 from deep sleep
• Retain state during deep sleep

Pin Selection Best Practices

For Digital Output (LED, Relay, etc.)

Best choices: 16, 17, 18, 19, 21, 22, 23, 25, 26, 27, 32, 33 Avoid: Strapping pins (0, 2, 5, 12, 15), input-only pins (34-39)

For Digital Input (Button, Sensor)

Best choices: 16, 17, 18, 19, 21, 22, 23, 25, 26, 27, 32, 33, 34, 35, 36, 39 Avoid: Strapping pins if possible

For PWM (Servo, Motor, LED dimming)

Best choices: 16, 17, 18, 19, 21, 22, 23, 25, 26, 27 Avoid: Strapping pins, input-only pins

For Analog Input (Sensors)

Best choices: 32, 33, 34, 35, 36, 39 (ADC1 - works with WiFi) Avoid: ADC2 pins if using WiFi (0, 2, 4, 12-15, 25-27)

For I2C

Default: SDA=21, SCL=22 (recommended to keep default) Alternative: Any GPIO pair except input-only pins

For SPI

Recommended: Use default VSPI pins (23, 19, 18, 5) Alternative: HSPI or custom pins

Power and Current

• Max current per GPIO: 40 mA (recommended 20 mA)
• Max total current: 200 mA across all pins
• Operating voltage: 3.3V logic level
• ⚠️ Never connect 5V signals directly - use level shifters

Pin Conflict Checker

Before assigning a pin, verify:

1. ✅ Pin supports required function (INPUT/OUTPUT/PWM/ADC/etc.)
2. ✅ Not an input-only pin if output needed (avoid 34, 35, 36, 39)
3. ✅ Not a strapping pin if possible (avoid 0, 2, 5, 12, 15)
4. ✅ Not already used by another peripheral in your project
5. ✅ If using WiFi, avoid ADC2 pins for analog input

Common Pin Assignments

Safe General Purpose Pins

These are the safest pins for most projects:

• GPIO 16, 17: Often free, good for general I/O
• GPIO 21, 22: I2C default but can be repurposed
• GPIO 23: VSPI MOSI but can be repurposed
• GPIO 25, 26: Have DAC if needed
• GPIO 32, 33: Good for analog or digital

Pins to Avoid

• GPIO 6-11: Connected to flash memory (SPI flash)
• GPIO 34-39: Input only
• GPIO 1, 3: UART0 (USB serial)

Hardware Errata

• ADC readings can be affected by WiFi activity (use ADC1)
• Some boards have LED on GPIO 2 that can interfere
• Touch sensor values vary with board design
• Deep sleep current depends on which pins are used