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https://github.com/mytechnotalent/Embedded-Hacking.git
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Add 0x09_dht11_rust: DHT11 temperature/humidity sensor driver
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Kevin Thomas
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//! @file dht11.rs
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//! @brief Implementation of DHT11 temperature and humidity sensor driver
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//! @author Kevin Thomas
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//! @date 2025
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//!
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//! MIT License
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//!
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//! Copyright (c) 2025 Kevin Thomas
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//!
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//! Permission is hereby granted, free of charge, to any person obtaining a copy
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//! of this software and associated documentation files (the "Software"), to deal
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//! in the Software without restriction, including without limitation the rights
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//! to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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//! copies of the Software, and to permit persons to whom the Software is
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//! furnished to do so, subject to the following conditions:
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//!
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//! The above copyright notice and this permission notice shall be included in
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//! all copies or substantial portions of the Software.
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//!
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//! THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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//! IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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//! FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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//! AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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//! LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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//! OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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//! SOFTWARE.
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/// Bit-duration threshold in microseconds.
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///
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/// If the high pulse is longer than this value, the bit is a 1; otherwise 0.
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pub const BIT_THRESHOLD_US: u32 = 40;
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/// Timeout in spin-loop iterations for waiting on a pin level change.
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pub const LEVEL_WAIT_TIMEOUT: u32 = 10_000;
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/// Accumulate a single received bit into the 5-byte data array.
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///
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/// Shifts `data[byte_index]` left by one and sets the LSB to 1 if the
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/// measured high-pulse `duration_us` exceeds [`BIT_THRESHOLD_US`].
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///
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/// # Arguments
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///
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/// * `data` - 5-byte array accumulating the received bits.
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/// * `bit_index` - Bit index (0..39).
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/// * `duration_us` - Measured duration of the high pulse in microseconds.
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pub fn accumulate_bit(data: &mut [u8; 5], bit_index: usize, duration_us: u32) {
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let byte = bit_index / 8;
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data[byte] <<= 1;
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if duration_us > BIT_THRESHOLD_US {
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data[byte] |= 1;
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}
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}
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/// Verify the DHT11 checksum byte.
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///
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/// The checksum (byte 4) must equal the lower 8 bits of the sum of
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/// bytes 0 through 3.
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///
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/// # Arguments
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///
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/// * `data` - 5-byte received data (bytes 0–3 plus checksum in byte 4).
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///
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/// # Returns
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///
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/// `true` if the checksum matches, `false` otherwise.
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pub fn validate_checksum(data: &[u8; 5]) -> bool {
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data[4] == (data[0].wrapping_add(data[1]).wrapping_add(data[2]).wrapping_add(data[3]))
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}
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/// Parse humidity from the raw DHT11 data bytes.
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///
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/// Humidity is encoded as an integer part in byte 0 and a fractional
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/// part (tenths) in byte 1.
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///
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/// # Arguments
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///
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/// * `data` - 5-byte received data.
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///
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/// # Returns
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///
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/// Humidity as a percentage (e.g. 65.3 for 65.3%).
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pub fn parse_humidity(data: &[u8; 5]) -> f32 {
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data[0] as f32 + data[1] as f32 * 0.1
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}
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/// Parse temperature from the raw DHT11 data bytes.
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///
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/// Temperature is encoded as an integer part in byte 2 and a fractional
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/// part (tenths) in byte 3.
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///
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/// # Arguments
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///
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/// * `data` - 5-byte received data.
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///
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/// # Returns
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///
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/// Temperature in degrees Celsius.
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pub fn parse_temperature(data: &[u8; 5]) -> f32 {
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data[2] as f32 + data[3] as f32 * 0.1
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}
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/// Format a sensor reading as `"Humidity: XX.X% Temperature: XX.X C"`.
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///
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/// # Arguments
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///
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/// * `buf` - Mutable byte slice (must be at least 40 bytes).
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/// * `humidity` - Humidity percentage.
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/// * `temperature` - Temperature in degrees Celsius.
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///
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/// # Returns
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///
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/// Number of bytes written into the buffer.
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pub fn format_reading(buf: &mut [u8], humidity: f32, temperature: f32) -> usize {
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let mut pos = 0;
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let prefix = b"Humidity: ";
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buf[pos..pos + prefix.len()].copy_from_slice(prefix);
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pos += prefix.len();
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pos += format_f32_1(&mut buf[pos..], humidity);
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let mid = b"% Temperature: ";
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buf[pos..pos + mid.len()].copy_from_slice(mid);
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pos += mid.len();
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pos += format_f32_1(&mut buf[pos..], temperature);
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let suffix = b" C";
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buf[pos..pos + suffix.len()].copy_from_slice(suffix);
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pos += suffix.len();
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pos
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}
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/// Format a failed-read error message.
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///
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/// # Arguments
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///
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/// * `buf` - Mutable byte slice (must be at least 42 bytes).
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/// * `gpio` - GPIO pin number to include in the message.
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///
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/// # Returns
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///
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/// Number of bytes written into the buffer.
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pub fn format_error(buf: &mut [u8], gpio: u8) -> usize {
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let mut pos = 0;
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let prefix = b"DHT11 read failed - check wiring on GPIO ";
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buf[pos..pos + prefix.len()].copy_from_slice(prefix);
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pos += prefix.len();
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pos += format_u8(&mut buf[pos..], gpio);
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pos
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}
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/// Format a `u8` as decimal ASCII digits.
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///
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/// # Arguments
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///
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/// * `buf` - Output buffer.
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/// * `val` - Value to format.
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///
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/// # Returns
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///
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/// Number of bytes written.
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fn format_u8(buf: &mut [u8], val: u8) -> usize {
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if val >= 100 {
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buf[0] = b'0' + val / 100;
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buf[1] = b'0' + (val / 10) % 10;
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buf[2] = b'0' + val % 10;
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3
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} else if val >= 10 {
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buf[0] = b'0' + val / 10;
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buf[1] = b'0' + val % 10;
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2
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} else {
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buf[0] = b'0' + val;
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1
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}
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}
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/// Format an `f32` with one decimal place (e.g. `"25.3"`).
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///
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/// # Arguments
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///
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/// * `buf` - Output buffer.
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/// * `val` - Value to format.
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///
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/// # Returns
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///
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/// Number of bytes written.
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fn format_f32_1(buf: &mut [u8], val: f32) -> usize {
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let scaled = (val * 10.0) as u32;
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let integer = scaled / 10;
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let frac = (scaled % 10) as u8;
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let mut pos = 0;
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if integer >= 100 {
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buf[pos] = b'0' + (integer / 100) as u8;
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pos += 1;
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}
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if integer >= 10 {
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buf[pos] = b'0' + ((integer / 10) % 10) as u8;
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pos += 1;
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}
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buf[pos] = b'0' + (integer % 10) as u8;
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pos += 1;
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buf[pos] = b'.';
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pos += 1;
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buf[pos] = b'0' + frac;
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pos += 1;
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pos
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}
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#[cfg(test)]
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mod tests {
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// Import all parent module items
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use super::*;
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#[test]
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fn accumulate_bit_zero_short_pulse() {
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let mut data = [0u8; 5];
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accumulate_bit(&mut data, 0, 30);
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assert_eq!(data[0], 0);
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}
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#[test]
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fn accumulate_bit_one_long_pulse() {
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let mut data = [0u8; 5];
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accumulate_bit(&mut data, 0, 70);
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assert_eq!(data[0], 1);
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}
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#[test]
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fn accumulate_bit_threshold_exact() {
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let mut data = [0u8; 5];
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accumulate_bit(&mut data, 0, BIT_THRESHOLD_US);
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assert_eq!(data[0], 0);
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}
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#[test]
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fn accumulate_bit_two_bits() {
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let mut data = [0u8; 5];
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accumulate_bit(&mut data, 0, 70);
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accumulate_bit(&mut data, 1, 30);
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assert_eq!(data[0], 0b10);
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}
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#[test]
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fn accumulate_bit_crosses_byte() {
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let mut data = [0u8; 5];
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accumulate_bit(&mut data, 7, 70);
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accumulate_bit(&mut data, 8, 70);
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assert_eq!(data[0], 1);
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assert_eq!(data[1], 1);
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}
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#[test]
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fn validate_checksum_valid() {
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let data = [0x28, 0x00, 0x1A, 0x00, 0x42];
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assert!(validate_checksum(&data));
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}
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#[test]
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fn validate_checksum_invalid() {
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let data = [0x28, 0x00, 0x1A, 0x00, 0xFF];
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assert!(!validate_checksum(&data));
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}
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#[test]
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fn validate_checksum_wraps() {
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let data = [0xFF, 0x01, 0x00, 0x00, 0x00];
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assert!(validate_checksum(&data));
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}
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#[test]
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fn parse_humidity_integer_only() {
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let data = [0x41, 0x00, 0x00, 0x00, 0x41];
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let h = parse_humidity(&data);
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assert!((h - 65.0).abs() < 0.01);
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}
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#[test]
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fn parse_humidity_with_fraction() {
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let data = [0x41, 0x03, 0x00, 0x00, 0x44];
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let h = parse_humidity(&data);
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assert!((h - 65.3).abs() < 0.01);
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}
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#[test]
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fn parse_temperature_integer_only() {
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let data = [0x00, 0x00, 0x19, 0x00, 0x19];
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let t = parse_temperature(&data);
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assert!((t - 25.0).abs() < 0.01);
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}
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#[test]
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fn parse_temperature_with_fraction() {
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let data = [0x00, 0x00, 0x19, 0x05, 0x1E];
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let t = parse_temperature(&data);
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assert!((t - 25.5).abs() < 0.01);
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}
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#[test]
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fn format_reading_typical() {
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let mut buf = [0u8; 48];
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let n = format_reading(&mut buf, 65.0, 25.0);
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assert_eq!(&buf[..n], b"Humidity: 65.0% Temperature: 25.0 C");
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}
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#[test]
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fn format_reading_with_fractions() {
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let mut buf = [0u8; 48];
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let n = format_reading(&mut buf, 65.3, 25.5);
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assert_eq!(&buf[..n], b"Humidity: 65.3% Temperature: 25.5 C");
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}
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#[test]
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fn format_error_gpio4() {
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let mut buf = [0u8; 48];
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let n = format_error(&mut buf, 4);
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assert_eq!(&buf[..n], b"DHT11 read failed - check wiring on GPIO 4");
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}
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#[test]
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fn format_error_gpio15() {
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let mut buf = [0u8; 48];
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let n = format_error(&mut buf, 15);
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assert_eq!(&buf[..n], b"DHT11 read failed - check wiring on GPIO 15");
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}
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#[test]
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fn format_u8_single_digit() {
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let mut buf = [0u8; 4];
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let n = format_u8(&mut buf, 4);
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assert_eq!(&buf[..n], b"4");
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}
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#[test]
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fn format_u8_two_digits() {
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let mut buf = [0u8; 4];
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let n = format_u8(&mut buf, 15);
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assert_eq!(&buf[..n], b"15");
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}
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#[test]
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fn format_u8_three_digits() {
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let mut buf = [0u8; 4];
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let n = format_u8(&mut buf, 255);
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assert_eq!(&buf[..n], b"255");
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}
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}
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