esp-rs embassy function for reading ultrasonic distance sensor JSN-SR04T / AJ-SR04M using mode 0 (pulse time)

jsn_aj-sr04-ping.rs

/*
  The following snipset is for reading the AJ-SR04M (JSN-SR04T compatible) ultrasonic distance sensor
  under rust (esp-rs + embassy).
  It is intended for mode 0 (which is the default) and it is counting the resulting echo pulse timing.
  Finaly the useconds value is converted to centimeters value.

  ESP32 wiring:
   Vcc -> 5V
   Trigger -> GPIO 19
   Echo -> GPIO 21 (via level shifter)
   Gnd -> gnd

  5V->3v3 level shifter for the echo pin done like this:
  https://wokwi.com/projects/364680888105225217
*/

#[entry]
fn main() -> ! {
    // standard initialization, watchdog disable, etc

    // Instantiate and Create Handle for IO
    let io = IO::new(peripherals.GPIO, peripherals.IO_MUX);

    // Instantiate and Create Handle for trigger output & echo input
    let mut trig = io.pins.gpio19.into_push_pull_output();
    let echo = io.pins.gpio21.into_floating_input();

    // Async requires the GPIO interrupt to wake futures
    hal::interrupt::enable(
        hal::peripherals::Interrupt::GPIO,
        hal::interrupt::Priority::Priority1,
    )
    .unwrap();
    
    // here you may start your task
    // and from there you can call the ping async function
    // which will return measured cm value...
    // tip: consider use use embassy_time::{with_timeout}
    // to be safe when the device will not give any feedback pulse
}

async fn ping(echo: &mut Gpio21<Input<Floating>>, trigger: &mut Gpio19<Output<PushPull>>) -> f64 {
    // 1) Set pin ouput to low for 5 us to get clean low pulse
    trigger.set_low().unwrap();
    Timer::after(Duration::from_micros(5)).await;
      
    // 2) Set pin output to high (trigger) for 20us
    trigger.set_high().unwrap();
    Timer::after(Duration::from_micros(20)).await;
    trigger.set_low().unwrap();

    echo.wait_for_rising_edge().await.unwrap();
    // Kick off timer measurement
    let echo_start = Instant::now();
    echo.wait_for_falling_edge().await.unwrap();
    // Collect current timer count (result pulse time)
    let delay = echo_start.elapsed().as_micros();

    // Calculate the distance in cms using formula in datasheet
    let distance_cm = ((delay * 348) as f64 / 2.0) / 10_000.0;

    distance_cm
}