Merge pull request #279 from jannic/dht11_example

Add an example reading a dht11 sensor

rp2040-hal/Cargo.toml

@@ -45,6 +45,7 @@ panic-halt = "0.2.0"
 rp2040-boot2 = "0.2.0"
 hd44780-driver = "0.4.0"
 pio-proc = "0.1.0"
+dht-sensor = "0.2.1"
 
 [features]
 rt = ["rp2040-pac/rt"]

rp2040-hal/examples/dht11.rs

@@ -0,0 +1,148 @@
+//! # DHT11 Example
+//!
+//! This application demonstrates how to read a DHT11 sensor on the RP2040.
+//!
+//! It may need to be adapted to your particular board layout and/or pin assignment.
+//! In this example, the DHT11 data pin should be connected to GPIO28.
+//!
+//! NOTE: The DHT11 driver only works reliably when compiled in release mode.
+//!
+//! See the `Cargo.toml` file for Copyright and licence details.
+
+#![no_std]
+#![no_main]
+
+// The macro for our start-up function
+use cortex_m_rt::entry;
+
+// Ensure we halt the program on panic (if we don't mention this crate it won't
+// be linked)
+use panic_halt as _;
+
+// Alias for our HAL crate
+use rp2040_hal as hal;
+
+// A shorter alias for the Peripheral Access Crate, which provides low-level
+// register access
+use hal::pac;
+
+// Some traits we need
+use embedded_hal::digital::v2::InputPin;
+use embedded_hal::digital::v2::OutputPin;
+use embedded_time::fixed_point::FixedPoint;
+use hal::gpio::dynpin::DynPin;
+use hal::Clock;
+
+/// The linker will place this boot block at the start of our program image. We
+/// need this to help the ROM bootloader get our code up and running.
+#[link_section = ".boot2"]
+#[used]
+pub static BOOT2: [u8; 256] = rp2040_boot2::BOOT_LOADER_W25Q080;
+
+/// External high-speed crystal on the Raspberry Pi Pico board is 12 MHz. Adjust
+/// if your board has a different frequency
+const XTAL_FREQ_HZ: u32 = 12_000_000u32;
+
+use dht_sensor::{dht11, DhtReading};
+
+/// A wrapper for DynPin, implementing both InputPin and OutputPin, to simulate
+/// an open-drain pin as needed by the wire protocol the DHT11 sensor speaks.
+/// https://how2electronics.com/interfacing-dht11-temperature-humidity-sensor-with-raspberry-pi-pico/
+struct InOutPin {
+    inner: DynPin,
+}
+
+impl InOutPin {
+    fn new(inner: DynPin) -> Self {
+        Self { inner }
+    }
+}
+
+impl InputPin for InOutPin {
+    type Error = rp2040_hal::gpio::Error;
+    fn is_high(&self) -> Result<bool, <Self as embedded_hal::digital::v2::InputPin>::Error> {
+        self.inner.is_high()
+    }
+    fn is_low(&self) -> Result<bool, <Self as embedded_hal::digital::v2::InputPin>::Error> {
+        self.inner.is_low()
+    }
+}
+
+impl OutputPin for InOutPin {
+    type Error = rp2040_hal::gpio::Error;
+    fn set_low(&mut self) -> Result<(), <Self as embedded_hal::digital::v2::OutputPin>::Error> {
+        // To actively pull the pin low, it must also be configured as a (readable) output pin
+        self.inner.into_readable_output();
+        // In theory, we should set the pin to low first, to make sure we never actively
+        // pull it up. But if we try it on the input pin, we get Err(Gpio(InvalidPinType)).
+        self.inner.set_low()?;
+        Ok(())
+    }
+    fn set_high(&mut self) -> Result<(), <Self as embedded_hal::digital::v2::OutputPin>::Error> {
+        // To set the open-drain pin to high, just disable the output driver by changing the
+        // pin to input mode with pull-up. That way, the DHT11 can still pull the data line down
+        // to send its response.
+        self.inner.into_pull_up_input();
+        Ok(())
+    }
+}
+
+/// Entry point to our bare-metal application.
+///
+/// The `#[entry]` macro ensures the Cortex-M start-up code calls this function
+/// as soon as all global variables are initialised.
+///
+/// The function configures the RP2040 peripherals, assigns GPIO 28 to the
+/// DHT11 driver, and takes a single measurement.
+#[entry]
+fn main() -> ! {
+    // Grab our singleton objects
+    let mut pac = pac::Peripherals::take().unwrap();
+    let core = pac::CorePeripherals::take().unwrap();
+
+    // Set up the watchdog driver - needed by the clock setup code
+    let mut watchdog = hal::Watchdog::new(pac.WATCHDOG);
+
+    // Configure the clocks
+    let clocks = hal::clocks::init_clocks_and_plls(
+        XTAL_FREQ_HZ,
+        pac.XOSC,
+        pac.CLOCKS,
+        pac.PLL_SYS,
+        pac.PLL_USB,
+        &mut pac.RESETS,
+        &mut watchdog,
+    )
+    .ok()
+    .unwrap();
+
+    // The single-cycle I/O block controls our GPIO pins
+    let sio = hal::Sio::new(pac.SIO);
+
+    // Set the pins to their default state
+    let pins = hal::gpio::Pins::new(
+        pac.IO_BANK0,
+        pac.PADS_BANK0,
+        sio.gpio_bank0,
+        &mut pac.RESETS,
+    );
+
+    let mut delay = cortex_m::delay::Delay::new(core.SYST, clocks.system_clock.freq().integer());
+
+    // Use GPIO 28 as an InOutPin
+    let mut pin = InOutPin::new(pins.gpio28.into());
+    pin.set_high().ok();
+
+    // Perform a sensor reading
+    let _measurement = dht11::Reading::read(&mut delay, &mut pin);
+
+    // In this case, we just ignore the result. A real application
+    // would do something with the measurement.
+
+    #[allow(clippy::empty_loop)]
+    loop {
+        // Empty loop
+    }
+}
+
+// End of file