ESP32 Pin Reference

Here is a pinout for an ESP32 Dev Kit. This is common module used for FluidNC controllers, but other version will work on controllers designed for them. This is a good reference of the capabilities of each pin.

See the end of the doc for other types.

Usable I/O pins

• GPIO_NUM_2
  • Some dev boards have an LED on this. It does not work well as an input, because the LED affects the voltage on the pin.
  • It must be either left unconnected/floating, or driven Low, in order to enter the serial bootloader.
  • I like to use it as the spindle pin. The LED gives a nice indication of the spindle on and PWM level.
• GPIO_NUM_4
• GPIO_NUM_5 - (Used by SD Card)
• GPIO_NUM_12
  • If driven High, flash voltage (VDD_SDIO) is 1.8V not default 3.3V. Has internal pull-down, so unconnected = Low = 3.3V. May prevent flashing and/or booting if 3.3V flash is used and this pin is pulled high, causing the flash to brownout. See the ESP32 datasheet for more details
• GPIO_NUM_13
• GPIO_NUM_14 (some pulses at boot)
• GPIO_NUM_15
  • Some pulses at boot
  • If driven Low, silences boot messages printed by the ROM bootloader. Has an internal pull-up, so unconnected = High = normal output
• GPIO_NUM_16
• GPIO_NUM_17
• GPIO_NUM_18 - (Used by SD Card)
• GPIO_NUM_19 - (Used by SD Card)
• GPIO_NUM_21
• GPIO_NUM_22
• GPIO_NUM_23 - (Used by SD Card)
• GPIO_NUM_25
• GPIO_NUM_26
• GPIO_NUM_27
• GPIO_NUM_32
• GPIO_NUM_33

Input Only (no pullup/pulldown)

If you do not have external pull up or pull down resistors. Do not use these pins!

• GPIO_NUM_34
• GPIO_NUM_35
• GPIO_NUM_36
• GPIO_NUM_37 (not typically available)
• GPIO_NUM_38 (not typically available)
• GPIO_NUM_39

Don't Use (or not recommended)

• GPIO_NUM_0 - This is used for the bootloader (Usable, but for experts only)
• GPIO_NUM_1 - Used for Serial Data
• GPIO_NUM_3 - Used for Serial Data
• GPIO_NUM_6 - Use for External Flash
• GPIO_NUM_7 - Use for External Flash
• GPIO_NUM_8 - Use for External Flash
• GPIO_NUM_9 - Use for External Flash
• GPIO_NUM_10 - Use for External Flash
• GPIO_NUM_11 - Use for External Flash
• GPIO_NUM_20 - This is not available on ESP32s
• GPIO_NUM_24 - This is not available on ESP32s
• GPIO_NUM_28 - This is not available on ESP32s
• GPIO_NUM_29 - This is not available on ESP32s
• GPIO_NUM_30 - This is not available on ESP32s
• GPIO_NUM_31 - This is not available on ESP32s

Other common modules.