dht-embedded

dht-embedded is a Rust crate that reads temperature and humidity data from the DHT11 and DHT22 sensors.

Prerequisites

• You've connected the DHT sensor to your device (such as a Raspberry Pi or ESP32) using a GPIO pin.

Usage

Add the following to your Cargo.toml:

[dependencies]
dht-embedded = "0.4"

This crate depends on the stabilized 1.x series of embedded-hal.

You will need to use an embedded-hal implementation for your hardware. Here's a simple one using linux-embedded-hal and gpio-cdev, which could be used on a Rasperry Pi.

use dht_embedded::{Dht22, DhtSensor, NoopInterruptControl};
use gpio_cdev::{Chip, LineRequestFlags};
use linux_embedded_hal::{CdevPin, Delay};
use std::{thread::sleep, time::Duration};

fn main() -> anyhow::Result<()> {
    let mut gpiochip = Chip::new("/dev/gpiochip0")?;
    let line = gpiochip.get_line(17)?;
    let handle = line.request(LineRequestFlags::INPUT | LineRequestFlags::OUTPUT, 1, "dht-sensor")?;
    let pin = CdevPin::new(handle)?;
    let mut sensor = Dht22::new(NoopInterruptControl, Delay, pin);

    loop {
        match sensor.read() {
            Ok(reading) => println!("{}°C, {}% RH", reading.temperature(), reading.humidity()),
            Err(e) => eprintln!("Error: {}", e),
        }

        sleep(Duration::from_millis(2100));
    }
}

Note that, if your hardware supports it, you should set the GPIO pin to "open drain" mode.

(To be fair, the Linux kernel includes a driver for DHT sensors, and honestly it's probably better to use that driver, since kernel space can disable interrupts and get much more precise timing than we can.)

Why

A search of crates.io might yield several different implementations of this driver. I wrote this because none of the others worked for me, and, upon examination of their code, I found they used a completely different protocols for reading from the sensor, protocols I couldn't find documented anywhere as what's supposed to work. This crate implements one of the simpler protocols that doesn't require access to a system clock, but still seems to work most of the time.