jessikitty
602028ed01
Which pins are in use, which are free, which are strapping or flash pins, and the per-pin current limits.
2.7 KiB
ESP32 pinout reference
For the original ESP32-WROOM-32 / WROVER devkit, which is what both boards in this project are. S3, C3, C6 and H2 have different maps entirely — and no Bluetooth Classic, so they cannot run board A at all.
Already in use
| Pin | Board | Used for |
|---|---|---|
| GPIO2 | A and B | onboard status LED |
| GPIO16 | A and B | UART2 RX (link) |
| GPIO17 | A and B | UART2 TX (link) |
| GPIO25 | B | LED circuit 1 (Circle) |
| GPIO26 | B | LED circuit 2 (Triangle) |
Free and safe for output
Use these first. No strapping duties, no boot-time side effects.
4 13 14 18 19 21 22 23 27 32 33
That is eleven spare pins, which is plenty for more LEDs, a buzzer, servos or switches. GPIO21 and GPIO22 are the default I2C pins and GPIO18/19/23 the default SPI pins, but nothing in this project uses either bus, so they are free here.
Never use
| Pin | Why |
|---|---|
| GPIO6–11 | wired to the on-board SPI flash chip. Touching these bricks the running firmware. |
| GPIO12 | strapping pin (MTDI). Pulled high at boot it sets the flash voltage to 1.8V and the board will not boot. |
| GPIO1, GPIO3 | UART0, the USB serial console. Using them breaks uploads and the serial monitor. |
Usable, with a catch
| Pin | Catch |
|---|---|
| GPIO0 | strapping. Must be high at boot or the board enters flash-download mode. Has a button on most devkits. |
| GPIO2 | strapping, and the onboard LED. Must be low or floating at boot. Fine as an output once running — this project uses it. |
| GPIO5 | strapping. Outputs a PWM burst during boot, so anything attached will twitch at power-on. |
| GPIO15 | strapping. Emits boot log noise unless pulled low. |
Input only — cannot drive an LED
34 35 36 39
These have no output drivers and no internal pull-ups. Fine for buttons with an external pull-up, or for analog input. Connect an LED and nothing happens.
Current limits
A single pin is comfortable at about 12mA and hard-limited near 40mA. The whole chip should stay under roughly 200mA across all pins at once.
Two or three small LEDs per pin is fine. Anything beyond about 20mA per circuit — which pre-wired "3V" LEDs sized for a coin cell often draw — wants a small NPN transistor or a logic-level MOSFET, with the pin driving the base or gate rather than the LED directly.
ADC note
ADC2 pins (0, 2, 4, 12–15, 25–27) cannot be read with analogRead() while
WiFi is active. Irrelevant to this project, which uses no WiFi and no analog
input, but worth knowing before adding a potentiometer. ADC1 pins (32–39) work
regardless.
Created by: Jess Rogerson (yelling commands at Claude.AI)