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Working with inputs

We have worked through an example of driving a GPIO output. Now it's time for you to try and extend the program to read the GPIO input state.

  • Use the esp_hal crate documentation to create and initialize a GPIO Input.
  • The button is connected to GPIO9.
  • Write a program that turns the LED on only while the button is pressed.
Solution
  1. Add new imports: 
    #![allow(unused)]
fn main() {
use esp_hal::gpio::{Input, InputConfig};
}
  2. Declare the button: 
    #![allow(unused)]
fn main() {
let button = Input::new(peripherals.GPIO9, InputConfig::default());
}
  3. Modify the loop code: 
    #![allow(unused)]
fn main() {
 if button.is_high() {
     led.set_high();
 } else {
     led.set_low();
 }
}

Explanation

You may be tempted to think that high means ON and low means off, however, the logic of both the button and the LED is inverted.

Button has a pull-up resistor and connects the pin to ground when pressed.

The LED has its anode connected to the 3.3 V supply and the cathode is connected to the open-drain output. When the output is set to low, it is connected to ground, allowing the current to flow and thereby turning the LED on.