Working with DHT22 with a ESP32 board always returns in an TIMEOUT

[yudistrange]

What happened?

I am trying to get readings from a DHT22 sensor using my ESP32 dev board. The result is always a timeout.
The board and the sensor are working. I have verified that by flashing LuaRTOS and getting the sensor to respond back with the temperature / humidity readings.

I looked at the specification of the sensor and then your driver. It mostly makes sense. The timeouts are in the correct range as per the sensor specification. I also tried to implement the specification on my own, but still got the same result. I also forked your repo and increased the timeout, just to ensure that the sensor is not slow. I am also only using the --release tag for optimized binary as talked about in this issue

So I think I may be missing out on some initial setup - setting the pins to be pull-down / pull-up, some other configuration 🤷

Are you aware of any such initialization steps that must be performed for the sensor to work?
Here's my repo that's using your driver.

[yudistrange]

I also used the wowki emulator for this, just to weed out any physical issues with the device.
The project can be found here. But the result is the same, TIMEOUT

[Danylo Kondratiev]

Reproducible on v0.2.1 and main branch. I use Wokwi emulator.

[Simon Klimaschka]

For anyone coming along this issue, the solution is to use the GPIO pin in open drain mode:

let mut sensor = gpio::PinDriver::input_output_od(pin).unwrap();   // instead of input_output(pin).unwrap()

[Mike Beaumont]

Would love to hear whether that solves it for others. This may depend on exactly how the sensor is wired but I think open drain is in fact required for the DHT. It's mentioned/used in both the README and the example.

[Louis Giët]

I have a similar issue on my Raspberry Pi Pico H.

I'm new to embedded and tried multiple crates which keep responding with timeouts.
Previously used dht-pio, which hasn't tested the DHT11 yet so I discovered this crate.

Didn't find the rp2040_hal crate referencing configuring pins for open drain so I guessed that pins.gpio28.into_push_pull_output() would to the trick.

My Code

#![no_std]
#![no_main]

use rp_pico as bsp;

use bsp::{entry, hal::clocks::ClockSource};
use defmt::*;
use defmt_rtt as _;
use dht_sensor::DhtReading;
use embedded_hal::digital::v2::OutputPin;
use panic_probe as _;

use bsp::hal::{clocks::init_clocks_and_plls, pac, sio::Sio, watchdog::Watchdog};

#[entry]
fn main() -> ! {
    let mut pac = pac::Peripherals::take().unwrap();
    let mut watchdog = Watchdog::new(pac.WATCHDOG);
    let clocks = init_clocks_and_plls(
        rp_pico::XOSC_CRYSTAL_FREQ,
        pac.XOSC,
        pac.CLOCKS,
        pac.PLL_SYS,
        pac.PLL_USB,
        &mut pac.RESETS,
        &mut watchdog,
    )
    .ok()
    .unwrap();

    let sio = Sio::new(pac.SIO);
    let pins = rp_pico::Pins::new(
        pac.IO_BANK0,
        pac.PADS_BANK0,
        sio.gpio_bank0,
        &mut pac.RESETS,
    );

    let core = pac::CorePeripherals::take().unwrap();
    let mut delay = cortex_m::delay::Delay::new(core.SYST, clocks.system_clock.get_freq().to_Hz());

    let mut dht11_pin = pins.gpio28.into_push_pull_output();
    match dht11_pin.set_high() {
        Ok(value) => info!("Set GPIO28 HIGH: {}", value),
        Err(err) => error!("Failed to set GPIO2 HIGH: {}", err),
    };

    loop {
        info!("Reading from DHT11");
        match dht_sensor::dht11::Reading::read(&mut delay, &mut dht11_pin) {
            Ok(data) => {
                debug!(
                    "Temp info:\nHumidity: {}\nTemperature: {}",
                    data.relative_humidity, data.temperature
                );
            }
            Err(error) => {
                match error {
                    dht_sensor::DhtError::Timeout => {
                        error!("Timeout");
                    }
                    dht_sensor::DhtError::PinError(_e) => error!("DHT PinError"),
                    dht_sensor::DhtError::ChecksumMismatch => error!("DHT ChecksumMismatch"),
                }
            }
        };

        delay.delay_ms(1000);
    }
}

My sensor setup

See Pico pin layout

Data: Green cable from DHT11 left pin to Pico pin 34 (GP28)
Power: Red cable from DHT11 middle pin to Pico pin 36 (3V out)
Ground: Black cable from DHT11 right pin to Pico pin 38 (GND)

[Mike Beaumont]

@Ziothh can you try gpio::InOutPin as used in the rp2040 DHT example?

[Louis Giët]

@michaelbeaumont That works! Thanks for the quick response!

[Sergio Gasquez Arcos]

For reference, here is a working Wokwi project with ESP32: https://wokwi.com/projects/384087992261474305