HC-SR04

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  <h1 align="center">HC-SR04</h1>

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This crate provides a driver for the **HC-SR04**/**HC-SR04P** ultrasonic
distance sensor on *Raspberry Pi*, using
[rppal](https://docs.rs/rppal/0.13.1/rppal/) to access Raspberry Pi's GPIO.

## Examples

Usage examples can be found in the 
[examples](https://github.com/marcoradocchia/hc-sr04/tree/master/examples)
folder.

## Measure distance
```rust
use hc_sr04::{HcSr04, Unit};

// Initialize driver.
let mut ultrasonic = HcSr04::new(
    24,          // TRIGGER -> Gpio pin 24
    23,          // ECHO -> Gpio pin 23
    Some(23_f32) // Ambient temperature (if `None` defaults to 20.0C)
).unwrap();

// Perform distance measurement, specifying measuring unit of return value.
match ultrasonic.measure_distance(Unit::Meters).unwrap() {
    Some(dist) => println!("Distance: {.2}m", dist),
    None => println!("Object out of range"),
}
```

## Calibrate measurement

Distance measurement can be calibrated at runtime using the `HcSr04::calibrate`
method that this library exposes, passing the current ambient temperature as
`f32`.

```rust
use hc_sr04::{HcSr04, Unit};

// Initialize driver.
let mut ultrasonic = HcSr04::new(24, 23, None).unwrap();

// Calibrate measurement with ambient temperature.
ultrasonic.calibrate(23_f32);

// Perform distance measurement.
match ultrasonic.measure_distance(Unit::Centimeters).unwrap() {
    Some(dist) => println!("Distance: {.1}cm", dist),
    None => println!("Object out of range"),
}
```