mq2_gas

ROS2 Jazzy driver for MQ-2 gas/smoke sensor via ADS1115 ADC (Analog).

The MQ-2 detects LPG, propane, methane, alcohol, hydrogen, and smoke. It outputs an analog voltage proportional to gas concentration, which is read via an external ADS1115 ADC. The driver converts the raw voltage to Rs/R0 ratio and approximate PPM using datasheet curve approximations.

Features

• Publishes std_msgs/Float32 on mq2/lpg_ppm (gas concentration)
• Publishes std_msgs/Float32 on mq2/voltage (raw sensor voltage)
• fake_mode for testing without hardware
• Rs/R0 ratio calculation with configurable RL, R0, VCC
• Datasheet log-log curve approximation for LPG and smoke
• Clean air calibration via service call
• Runtime publish_rate change via ros2 param set

Prerequisites

• ROS 2 Jazzy
• Python 3
• smbus2 (pip install smbus2) — only needed for real hardware
• ADS1115 ADC connected to MQ-2 analog output

Installation

cd ~/ros2_ws
colcon build --packages-select mq2_gas --symlink-install
source install/setup.bash

Usage

Launch (default: fake_mode)

ros2 launch mq2_gas mq2_launch.py

Direct execution

ros2 run mq2_gas mq2_node.py --ros-args -p fake_mode:=true

Real hardware (Raspberry Pi + ADS1115)

ros2 launch mq2_gas mq2_launch.py params_file:=my_params.yaml

YAML override

mq2_gas_node:
  ros__parameters:
    fake_mode: false
    adc_channel: 0
    vcc: 5.0
    rl: 10.0
    r0: 9.8    # Calibrated R0 value

Topic echo

ros2 topic echo /mq2/lpg_ppm
ros2 topic echo /mq2/voltage

Parameters

Parameter	Type	Default	Description
fake_mode	bool	true	Use fake driver (no hardware)
i2c_bus	int	1	I2C bus number
adc_address	int	0x48	ADS1115 I2C address
adc_channel	int	0	ADS1115 channel (0–3)
pga_gain	int	1	ADS1115 PGA (1=±4.096V)
publish_rate	double	1.0	Publishing rate (Hz)
vcc	double	5.0	Supply voltage (V)
rl	double	10.0	Load resistance (kOhm)
r0	double	10.0	Sensor resistance in clean air (kOhm)

Services

Service	Type	Description
mq2/calibrate	std_srvs/srv/Trigger	Collect samples in clean air, set PPM baseline
mq2/reset	std_srvs/srv/Trigger	Clear bias, reinitialise sensor

Package Structure

mq2_gas/
├── CMakeLists.txt
├── CONTRIBUTING.md
├── LICENSE
├── README.md
├── .gitignore
├── package.xml
├── config/
│   └── mq2_params.yaml
├── launch/
│   └── mq2_launch.py
├── nodes/
│   └── mq2_node.py
├── mq2_gas/
│   ├── __init__.py
│   └── mq2_driver.py
└── test/
    └── test_mq2_node.py

Test Results

Tested on Ubuntu 24.04 (WSL2) with fake_mode: true.

Test Category	Test	Result
Topics	mq2/lpg_ppm publishes std_msgs/Float32	PASS
Topics	mq2/voltage publishes std_msgs/Float32	PASS
Services	mq2/calibrate returns success=True	PASS
Services	mq2/reset returns success=True	PASS
Parameters	publish_rate runtime change	PASS
Shutdown	Clean exit	PASS
Linting	pep257, flake8, copyright, xmllint	PASS

License

MIT