embedded-dht-rs 0.1.0

A platform agnostic driver to interface with the DHT11/DHT22 (AM2302) temperature and humidity sensor
Documentation

embedded-dht-rs

Welcome to embedded-dht-rs, a Rust library designed to make working with DHT sensors a breeze!

This library only depends on embedded_hal, making it versatile and compatible with virtually any microcontroller.

Features:

  • DHT11 sensor support: Fully implemented and ready to use.
  • DHT22 sensor support: Currently in progress – stay tuned!

We’ve tested it with the ESP32-WROOM, and you can find a detailed example below to help you get started.

Getting Started

Example

#![no_std]
#![no_main]

use embedded_dht_rs::Dht11;
use esp_backtrace as _;
use esp_hal::{
    clock::ClockControl,
    delay::Delay,
    gpio::{Io, Level, OutputOpenDrain, Pull},
    peripherals::Peripherals,
    prelude::*,
    system::SystemControl,
};
#[entry]
fn main() -> ! {
    let peripherals = Peripherals::take();
    let system = SystemControl::new(peripherals.SYSTEM);
    let clocks = ClockControl::boot_defaults(system.clock_control).freeze();
    let io = Io::new(peripherals.GPIO, peripherals.IO_MUX);

    esp_println::logger::init_logger_from_env();

    let delay = Delay::new(&clocks);

    let gpio4 = OutputOpenDrain::new(io.pins.gpio4, Level::High, Pull::None);
    let mut led_sensor = Dht11::new(gpio4, delay);

    loop {
        delay.delay(1000.millis());
        let reading = led_sensor.read().unwrap();
        log::info!(
            "Temperature: {}, humidity: {}",
            reading.temperature,
            reading.humidity
        );
    }
}

steps

Step 1

After powering on the DHT11 (once powered, allow 1 second to pass during which the sensor stabilizes; during this time, no commands should be sent), it measures the temperature and humidity of the surrounding environment and stores the data. Meanwhile, the DATA line of the DHT11 is kept high by a pull-up resistor. The DATA pin of the DHT11 is in input mode, ready to detect any external signals.

Step 2

The microprocessor's I/O pin is set to output mode and pulled low, holding this state for at least 18 milliseconds. Then, the microprocessor's I/O is switched to input mode. Due to the pull-up resistor, the microprocessor’s I/O line and the DHT11 DATA line will remain high, waiting for the DHT11 to respond with a signal, as illustrated below:

step2

Step 3

The DHT11’s DATA pin detects an external signal and goes low, indicating that it is waiting for the external signal to complete. Once the signal ends, the DHT11’s DATA pin switches to output mode, producing a low signal for 80 microseconds as a response. This is followed by an 80-microsecond high signal, notifying the microprocessor that the sensor is ready to transmit data. At this point, the microprocessor's I/O pin, still in input mode, detects the low signal from the DHT11 (indicating the response) and then waits for the 80-microsecond high signal to start receiving data. The sequence of signal transmission is illustrated below:

step3

Step 4

The DHT11 outputs 40 bits of data through the DATA pin, and the microprocessor receives these 40 data bits. The format for a data bit "0" consists of a low level lasting 50 microseconds, followed by a high level lasting 26-28 microseconds, depending on changes in the I/O level. For a data bit "1," the format includes a low level of 50 microseconds followed by a high level lasting up to 70 microseconds. The signal formats for data bits "0" and "1" are shown below.

step4

End signal

After outputting a low signal for 50 microseconds, the DHT11 completes sending the 40 bits of data and switches the DATA pin back to input mode, which, along with the pull-up resistor, returns to a high state. Meanwhile, the DHT11 internally re-measures the environmental temperature and humidity, records the new data, and waits for the next external signal.

Example Schematic

step3