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