dht_sensor/
read.rs

1use embedded_hal::blocking::delay::{DelayMs, DelayUs};
2use embedded_hal::digital::v2::{InputPin, OutputPin};
3
4#[derive(Debug)]
5pub enum DhtError<E> {
6    PinError(E),
7    ChecksumMismatch,
8    Timeout,
9}
10
11impl<E> From<E> for DhtError<E> {
12    fn from(error: E) -> DhtError<E> {
13        DhtError::PinError(error)
14    }
15}
16
17pub trait Delay: DelayUs<u8> + DelayMs<u8> {}
18impl<T> Delay for T where T: DelayMs<u8> + DelayUs<u8> {}
19
20pub trait InputOutputPin<E>: InputPin<Error = E> + OutputPin<Error = E> {}
21impl<T, E> InputOutputPin<E> for T where T: InputPin<Error = E> + OutputPin<Error = E> {}
22
23fn read_bit<E>(delay: &mut dyn Delay, pin: &impl InputPin<Error = E>) -> Result<bool, DhtError<E>> {
24    wait_until_timeout(delay, || pin.is_high(), 100)?;
25    delay.delay_us(35u8);
26    let high = pin.is_high()?;
27    wait_until_timeout(delay, || pin.is_low(), 100)?;
28    Ok(high)
29}
30
31fn read_byte<E>(delay: &mut dyn Delay, pin: &impl InputPin<Error = E>) -> Result<u8, DhtError<E>> {
32    let mut byte: u8 = 0;
33    for i in 0..8 {
34        let bit_mask = 1 << (7 - (i % 8));
35        if read_bit(delay, pin)? {
36            byte |= bit_mask;
37        }
38    }
39    Ok(byte)
40}
41
42pub fn read_raw<P, E>(delay: &mut dyn Delay, pin: &mut P) -> Result<[u8; 4], DhtError<E>>
43where
44    P: InputOutputPin<E>,
45{
46    pin.set_low().ok();
47    delay.delay_ms(18_u8);
48    pin.set_high().ok();
49    delay.delay_us(48_u8);
50
51    wait_until_timeout(delay, || pin.is_high(), 100)?;
52    wait_until_timeout(delay, || pin.is_low(), 100)?;
53
54    let mut data = [0; 4];
55    for b in data.iter_mut() {
56        *b = read_byte(delay, pin)?;
57    }
58    let checksum = read_byte(delay, pin)?;
59    if data.iter().fold(0u8, |sum, v| sum.wrapping_add(*v)) != checksum {
60        Err(DhtError::ChecksumMismatch)
61    } else {
62        Ok(data)
63    }
64}
65
66/// Wait until the given function returns true or the timeout is reached.
67fn wait_until_timeout<E, F>(
68    delay: &mut dyn Delay,
69    func: F,
70    timeout_us: u8,
71) -> Result<(), DhtError<E>>
72where
73    F: Fn() -> Result<bool, E>,
74{
75    for _ in 0..timeout_us {
76        if func()? {
77            return Ok(());
78        }
79        delay.delay_us(1_u8);
80    }
81    Err(DhtError::Timeout)
82}
dht_sensor/read.rs

dht_sensor/
read.rs
