sensor-w1therm

A C implementation of the w1_therm temperature sensor reader for WildlifeSystems.

Description

This program reads temperature data from 1-Wire temperature sensors connected to the system via the Linux kernel w1_therm driver interface. It outputs readings in JSON format compatible with the WildlifeSystems sensor-control framework.

Supported sensors:

• DS18S20 (family code 0x10)
• DS1822 (family code 0x22)
• DS18B20 (family code 0x28)
• DS1825 (family code 0x3B)
• DS28EA00 (family code 0x42)

Building

make

Installing

sudo make install

This installs the binary to /usr/bin/sensor-w1therm and the man page to /usr/share/man/man1/sensor-w1therm.1.

Uninstalling

sudo make uninstall

Usage

Enable 1-Wire interface (first-time setup)

sudo sensor-w1therm enable

This adds the w1-gpio overlay to /boot/firmware/config.txt. A reboot is required.

Read all connected sensors

sensor-w1therm

Output example:

[{"sensor":"ds18b20","measures":"temperature","unit":"Celsius","sensor_id":"28-0123456789ab","value":23.500}]

Filter by location

# Read only internal sensors
sensor-w1therm internal

# Read only external sensors
sensor-w1therm external

# Read all sensors explicitly
sensor-w1therm all

Configure sensors for fast reading

sensor-w1therm setup

This is run automatically on boot by the systemd service.

List supported measurements

sensor-w1therm list

Identify sensor type (for sensor-control integration)

sensor-w1therm identify

Returns exit code 60.

Show version

sensor-w1therm version

Output mock data for testing

sensor-w1therm mock

Hardware Configuration

1. Enable 1-Wire interface:

   sudo sensor-w1therm enable

2. Reboot the Raspberry Pi

Sysfs Interface

The program uses the Linux kernel w1_therm driver sysfs interface:

• /sys/bus/w1/devices/*/w1_slave - Traditional interface with CRC check
• /sys/bus/w1/devices/*/temperature - Direct temperature reading in millidegrees
• /sys/bus/w1/devices/w1_bus_master1/therm_bulk_read - Bulk conversion trigger

For more information, see the kernel documentation.

Error Handling

The program detects and reports the following error conditions:

• Startup value (85.0°C): Indicates the sensor has not completed a conversion yet
• Insufficient power (127.937°C): Indicates the kernel driver detected a power or bus error (not that the sensor is completely unpowered)

Building the Debian Package

From within the sensor-w1therm directory:

debuild -us -uc -b

Dependencies

• Linux kernel with w1_therm driver
• POSIX threads library (pthread)
• GCC compiler

License

GPL-2.0-or-later

Documentation

Comparison with older Bash version

Author

Ed Baker ed@ebaker.me.uk

Project

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

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