GPIO

• GPIO pin as GND and 3v3
  • As GND
  • As 3v3
• Pull-up and pull-down resistors
• References

GPIO pin as GND and 3v3

You can power sensors and other low-draw components on GPIO pins alone. On the ESP32 the GPIO pins can usually supply up to around $10mA$ or so, but the "real" 3v3 pin can supply more. It's really just doable for some low-power sensors.

As GND

To configure a pin as GND, you just have to define it as an output pin that has not been turned on:

output:
  - platform: gpio
    id: fake_gnd
    pin:
      number: ${gpio}
      mode:
        pulldown: true
        output: true

Somewhat confusingly, the pin must be defined as output. Enable pulldown in the pin config when using it as GND.

As 3v3

There are several ways to configure a GPIO pin as a $3.3V$ source. The simplest way is to configure the pin as inverted:

output:
  - platform: gpio
    id: supply_3v3
    pin:
      number: ${gpio}
      inverted: true
      mode:
        # Optionally set the maximum amount of current (esp-idf only)
        drive_strength: 40mA
        pullup: true
        output: true

Enabaling pullup activates the internal pull-up resistor on ESP32 boards, which is a $10k\Omega$ resistor from the GPIO to 3v3.

If you configure the output without inverted it will be LOW on boot, needing an on_boot automation to turn_on and pull it up to HIGH.

output:
  - platform: gpio
    id: supply_3v3
    pin:
      number: ${gpio}
      mode:
        pullup: true
        output: true

esphome:
  on_boot:
    priority: 90
    #  800: hardware init, vital components
    #  600: most sensors are ready
    #  250: wifi is initialized
    #  200: network connections and the esphome tcp api are set up
    #  100: everything is initialized
    then:
      - output.turn_on: supply

Another way is to just use the pin in an gpio switch:

switch:
  - platform: gpio
    id: supply_3v3
    name: "${hostname} GPIO 3v3"
    pin:
      number: ${gpio}
      mode:
        pullup: true
        output: true

Unless internal is enabled, this will show up and work like a regular switch entity in Home Assistant, so it can be turned on/off at will.

Both of these methods are useful for strapping pins as they avoid setting the state of the pin in flash and do it at runtime instead.

Pull-up and pull-down resistors

A pull-up resistor sits between GPIO and $VDD$/3V3 and "pulls up to positive", while a pull-down resistor sits between GPIO and GND and "pulls down to negative" instead.

Schematic by tom_l on Home Assistant forum⁸.

ESP32 has internal $10k\Omega$ pull-up/pull-down resistors that do this internally on the board (but ESP8266 does not have them).

binary_sensor:
  - platform: gpio
    id: binary_sensor_gpio
    name: "Press"
    pin:
      number: "${gpio_pin}"
      inverted: true
      mode:
        input: true
        pullup: true
        pulldown: false
    publish_initial_state: true

Configuring the pin with pulldown will activate this internal resistor on the ESP32 and connect the GPIO pin to the (real) GND with a $10k\Omega$ resistance.

References