sensor-dht11

A lightweight C implementation for reading DHT11 temperature and humidity sensors on Raspberry Pi.

Building from source

make

Installing

From source

sudo make install

From Debian package

Add the WildlifeSystems APT repository to your system

sudo apt update
sudo apt install sensor-dht11

Usage

Read sensors

# Read all sensors (temperature and humidity)
sensor-dht11

# Read all sensors explicitly
sensor-dht11 all

# Read only temperature
sensor-dht11 temperature

# Read only humidity
sensor-dht11 humidity

# Read only internal sensors
sensor-dht11 internal

# Read only external sensors
sensor-dht11 external

# List available sensor types
sensor-dht11 list

# Identify (exits with code 60)
sensor-dht11 identify

# Show version
sensor-dht11 version

# Output mock data for testing
sensor-dht11 mock

Configuration

Configuration is read from /etc/ws/sensors/dht11.json. Example:

[
  {
    "pin": 4,
    "internal": false
  }
]

Configuration options

• pin: GPIO pin number (2-27)
• internal: Boolean indicating if sensor is inside the enclosure
• sensor_id: Optional custom sensor ID (defaults to Pi serial + "_dht11")

Output

The program outputs JSON in the WildlifeSystems sensor format:

[
  {"sensor":"dht11_temperature","measures":"temperature","unit":"Celsius","value":23.0,"internal":false,"sensor_id":"1234567890abcdef_dht11_temperature"},
  {"sensor":"dht11_humidity","measures":"humidity","unit":"percentage","value":45.0,"internal":false,"sensor_id":"1234567890abcdef_dht11_humidity"}
]

How it works

This program uses a userspace C implementation to read DHT11 sensors via GPIO using the libgpiod library. All timing-critical bit-banging is handled in userspace with SCHED_FIFO real-time scheduling to minimise preemption-related timing failures.

Exit codes

• 0: Success
• 20: Invalid argument
• 60: Identify command

Documentation

Performance comparison between C and previous Python versions

Author

Ed Baker ed@ebaker.me.uk

Project

Part of the WildlifeSystems project. For more information, visit:

• https://wildlife.systems
• https://docs.wildlife.systems