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Vaishnav-sabari-girish
Vaishnav-sabari-girish

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Embedded Rust on the ESP32 : Sensor Integration : DHT22 (Temperature and Humidity Sensor)

#sensor #embeddedsystems #rust #esp32

In my previous blog, we interfaced a button.

We shall now get started with interfacing a few sensors. This blog will walk you through interfacing the DHT22 temperature and Humidity Sensor.

Getting Started

Let us create our new project

esp-generate --chip=esp32 dht22_sensor
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Open src/bin/main.rs and type the below code

#![no_std] #![no_main] #![deny( clippy::mem_forget, reason = "mem::forget is generally not safe to do with esp_hal types, especially those \ holding buffers for the duration of a data transfer." )] use esp_backtrace as _; use esp_hal::{ clock::CpuClock, delay::Delay, gpio::{DriveMode, Output, OutputConfig, Pull}, main, }; use esp_println::println; use embedded_dht_rs::dht22; esp_bootloader_esp_idf::esp_app_desc!(); #[main] fn main() -> ! { let config = esp_hal::Config::default().with_cpu_clock(CpuClock::max()); let peripherals = esp_hal::init(config); let od_config = OutputConfig::default() .with_drive_mode(DriveMode::OpenDrain) .with_pull(Pull::None); let od_for_dht22 = Output::new( peripherals.GPIO4, esp_hal::gpio::Level::High, od_config ) .into_flex(); od_for_dht22.peripheral_input(); let delay = Delay::new(); let mut dht22 = dht22::Dht22::new(od_for_dht22, delay); loop { delay.delay_millis(2000); println!(""); match dht22.read() { Ok(sensor_reading) => println!( "DHT22 Sensor - Temperature: {} C , Humidity: {} %", sensor_reading.temperature, sensor_reading.humidity ), Err(error) => println!("An error occurred while trying to read the sensor"), } println!("_____________________________________________________"); } }
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Output GIF

Output GIF

Into the code : Line-by-line explanation 

#![no_std]
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  • Disables the Rust standard library for embedded programming. 
#![no_main]
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  • Replaces the default main entry point with a custom embedded one. 
#![deny( clippy::mem_forget, reason = "mem::forget is generally not safe to do with esp_hal types, especially those \ holding buffers for the duration of a data transfer." )]
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  • Prevents the use of mem::forget as it can cause unsafe behavior in this context. 
use esp_backtrace as _;
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  • Enables backtrace support on panic (if supported by target). as _ suppresses warnings. 
use esp_hal::{ clock::CpuClock, delay::Delay, gpio::{DriveMode, Output, OutputConfig, Pull}, main, };
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  • Imports required ESP HAL modules:
    • Clock configuration
    • Delay handling
    • GPIO configuration (including open-drain and pull options)
    • main macro 
use esp_println::println;
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  • Enables UART-based printing to a terminal. 
use embedded_dht_rs::dht22;
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  • Imports DHT22 support from the embedded_dht_rs crate. 
esp_bootloader_esp_idf::esp_app_desc!();
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  • Embeds metadata about the application (like name, version). 
#[main] fn main() -> ! {
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  • Entry point of the embedded program that never returns (-> !). 
 let config = esp_hal::Config::default().with_cpu_clock(CpuClock::max());
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  • Configures system with maximum CPU clock speed. 
 let peripherals = esp_hal::init(config);
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  • Initializes the HAL and returns access to hardware peripherals. 
 let od_config = OutputConfig::default() .with_drive_mode(DriveMode::OpenDrain) .with_pull(Pull::None);
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  • Sets up GPIO pin as Open-Drain with no internal pull-up/down. This is essential for DHT22 communication. 
 let od_for_dht22 = Output::new( peripherals.GPIO4, esp_hal::gpio::Level::High, od_config ) .into_flex();
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  • Initializes GPIO4 with the config above and converts it to a flexible IO pin (Flex), which allows bidirectional control. 
 od_for_dht22.peripheral_input();
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  • Enables input mode for this flexible pin — DHT22 is bidirectional, so the pin needs to receive data too. 
 let delay = Delay::new();
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  • Creates a delay instance for timing control. 
 let mut dht22 = dht22::Dht22::new(od_for_dht22, delay);
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  • Initializes the DHT22 driver with the GPIO and delay. 
 loop {
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  • Begins infinite polling loop. 
 delay.delay_millis(2000);
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  • Waits 2 seconds between each sensor read (recommended minimum delay for DHT22). 
 println!("");
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  • Prints a blank line for readability. 
 match dht22.read() {
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  • Tries to read temperature and humidity from the sensor. 
 Ok(sensor_reading) => println!( "DHT22 Sensor - Temperature: {} C , Humidity: {} %", sensor_reading.temperature, sensor_reading.humidity ),
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  • If read is successful, prints temperature and humidity. 
 Err(error) => println!("An error occurred while trying to read the sensor"),
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  • If read fails, prints a basic error message (you can expand this with {:?} for debugging). 
 println!("_____________________________________________________");
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  • Prints a separator line to visually break up readings. 
 } }
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  • Closes loop and function.

Summary:

This ESP32 firmware reads data from a DHT22 sensor connected to GPIO4 and prints temperature and humidity to the serial console every 2 seconds. It uses open-drain GPIO configuration and the embedded_dht_rs crate for protocol handling.

Thank You

Important Links

  1. Getting Started Blog
  2. Interfacing a Button Blog
  3. GitHub Repository

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