By name: esp32 description: ESP32 hardware platform specifications including GPIO pins, PWM capabilities, ADC/DAC, communication interfaces, and hardware constraints. Reference this when generating code for ESP32 or validating pin configurations. user-invocable: false
ESP32 DevKit V1 Hardware Platform
Core Specifications
- MCU: ESP32-WROOM-32 (Dual-core Xtensa LX6)
- Operating Voltage: 3.3V (⚠️ NOT 5V tolerant)
- Clock Speed: 240 MHz (dual-core, adjustable)
- Flash Memory: 4 MB
- SRAM: 520 KB
- ROM: 448 KB
- Built-in Peripherals: WiFi 802.11 b/g/n, Bluetooth v4.2 BR/EDR and BLE
GPIO Pin Capabilities
Digital GPIO Pins
Available: GPIO 0-39 (40 pins total)
Usable for general I/O: 0-5, 12-19, 21-23, 25-27, 32-39
PWM-Capable Pins
All GPIO pins support PWM via LEDC peripheral (16 independent channels, 0-15)
- 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:
- ✅ Pin supports required function (INPUT/OUTPUT/PWM/ADC/etc.)
- ✅ Not an input-only pin if output needed (avoid 34, 35, 36, 39)
- ✅ Not a strapping pin if possible (avoid 0, 2, 5, 12, 15)
- ✅ Not already used by another peripheral in your project
- ✅ 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