w1thermsensor 2.3.0

A Python package and CLI tool to work with w1 temperature sensors like DS1822, DS18S20 & DS18B20 on the Raspberry Pi, Beagle Bone and other devices.

W1ThermSensor

Get the temperature from your w1 therm sensor in a single line of code!
It's designed to be used with the Rasperry Pi hardware but also works on a Beagle Bone and others.

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Raspberry Pi: this package is available in Raspbian as python-w1thermsensor and python3-w1thermsensor.

Python 2 drop: all w1thermsensor releases from 2.0 are Python 3.5+

Supported devices

The following w1 therm sensor devices are supported:

• DS18S20
• DS1822
• DS18B20
• DS28EA00
• DS1825/MAX31850K

Setup

The following hardware is needed:

• w1 therm compatible sensor (some of them can be bought here: Adafruit: DS18B20)
• wires to connect the sensor to your board (you might need a breadboard, too)
• a board like the Raspberry Pi or the Beagle Bone

On the Raspberry Pi, you will need to add dtoverlay=w1-gpio (for regular connection) or dtoverlay=w1-gpio,pullup="y" (for parasitic connection) to your /boot/config.txt. The default data pin is GPIO4 (RaspPi connector pin 7), but that can be changed from 4 to x with dtoverlay=w1-gpio,gpiopin=x.

After that, don't forget to reboot.

Hardware-connection

Raspi VCC (3V3) Pin 1 -----------------------------   VCC    DS18B20
                                               |
                                               |
                                               R1 = 4k7 ...10k
                                               |
                                               |
Raspi GPIO 4    Pin 7 -----------------------------   Data   DS18B20
       (BCM)    (BOARD)

Raspi GND       Pin 6 -----------------------------   GND    DS18B20

Soft-pull-up

Alternatively to the hardware pull-up made by a physical resistor, or to the above mentioned software configuration dtoverlay=w1-gpio,pullup="y" in /boot/config.txt, the following soft pull-up can be used:

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(4, GPIO.IN, pull_up_down=GPIO.PUD_UP)

When using this software pull-up, 1-Wire devices will be visible to the kernel only while the program pulls the GPIO pin up.

Hw device connection verification

Run the following command:

ls -l /sys/bus/w1/devices

You should check the availability of one or more filenames starting with "28-".

Filenames starting with "00-" possibly mean that the pull-up resistor is missing.

1-Wire devices can be plugged in dynamically and are visible to the kernel driver just after their hw connection.

To test reading the temperature, issue the following command:

for i in /sys/bus/w1/devices/28-*; do cat $i/w1_slave; done

Installation

From PIP

This possibility is supported on all distributions:

pip install w1thermsensor

Note: maybe root privileges are required

Use the async extra to add support for asyncio and AsyncW1ThermSensor:

pip install w1thermsensor[async]

On Raspbian using apt-get

If you are using the w1thermsensor module on a Rasperry Pi running Raspbian you can install it from the official repository:

sudo apt-get install python3-w1thermsensor

Note: For older versions of this package you might get the following error: ImportError: No module named 'pkg_resources' which indicates that you need to install python-setuptools or python3-setuptools respectively.

Manually build and install the debian package

debuild -us -uc
dpkg -i ../python3-w1thermsensor_*.deb

Usage as python package

The usage is very simple and the interface clean.. All examples are with the DS18B20 sensor - It works the same way for the other supported devices.

Basic usage with one sensor (implicit)

from w1thermsensor import W1ThermSensor, Unit

sensor = W1ThermSensor()
temperature_in_celsius = sensor.get_temperature()
temperature_in_fahrenheit = sensor.get_temperature(Unit.DEGREES_F)
temperature_in_all_units = sensor.get_temperatures([
    Unit.DEGREES_C,
    Unit.DEGREES_F,
    Unit.KELVIN])

The need kernel modules will be automatically loaded in the constructor of the W1ThermSensor class.
If something went wrong an exception is raised.

The first found sensor will be taken

Basic usage with one sensor (explicit)

The DS18B20 sensor with the ID 00000588806a will be taken.

from w1thermsensor import W1ThermSensor, Sensor

sensor = W1ThermSensor(sensor_type=Sensor.DS18B20, sensor_id="00000588806a")
temperature_in_celsius = sensor.get_temperature()

Multiple sensors

With the get_available_sensors class-method you can get the ids of all available sensors.

from w1thermsensor import W1ThermSensor

for sensor in W1ThermSensor.get_available_sensors():
    print("Sensor %s has temperature %.2f" % (sensor.id, sensor.get_temperature()))

Only sensors of a specific therm sensor type:

from w1thermsensor import W1ThermSensor, Sensor

for sensor in W1ThermSensor.get_available_sensors([Sensor.DS18B20]):
    print("Sensor %s has temperature %.2f" % (sensor.id, sensor.get_temperature()))

Set sensor resolution

Some w1 therm sensors support changing the resolution for the temperature reads. w1thermsensor enables to do so with the W1ThermSensor.set_resolution() method:

sensor = W1ThermSensor(sensor_type=Sensor.DS18B20, sensor_id="00000588806a")
sensor.set_resolution(9)

If the persist argument is set to False this value is "only" stored in the volatile SRAM, so it is reset when the sensor gets power-cycled.

If the persist argument is set to True the current set resolution is stored into the EEPROM. Since the EEPROM has a limited amount of writes (>50k), this command should be used wisely.

sensor = W1ThermSensor(sensor_type=Sensor.DS18B20, sensor_id="00000588806a")
sensor.set_resolution(9, persist=True)

Note: this is supported since Linux Kernel 4.7
Note: this requires root privileges

Disable kernel module auto loading

Upon import of the w1thermsensor package the w1-therm and w1-gpio kernel modules get loaded automatically. This requires the python process to run as root. Sometimes that's not what you want, thus you can disable the auto loading and load the kernel module yourself prior to talk to your sensors with w1thermsensor.

You can disable the auto loading feature by setting the W1THERMSENSOR_NO_KERNEL_MODULE environment variable to 1:

# set it globally for your shell so that sub-processes will inherit it.
export W1THERMSENSOR_NO_KERNEL_MODULE=1

# set it just for your Python process
W1THERMSENSOR_NO_KERNEL_MODULE=1 python my_awesome_thermsensor_script.py

Every other values assigned to W1THERMSENSOR_NO_KERNEL_MODULE will case w1thermsensor to load the kernel modules.

Note: the examples above also apply for the CLI tool usage. See below.

Correcting Temperatures / Sensor Calibration

Calibrating the temperature sensor relies on obtaining a measured high and measured low value that have known reference values that can be used for correcting the sensor's readings. The simplest way to do this is to measure the melting point and boiling point of water since those values are known. This method will only work with waterproof sensors - you will need a different mechanism for obtaining measured values if you are not using a waterproof sensor.

In order to obtain the measured_low_point, fill a container to 80% with ice and add water to the ice until the ice is floating and water is at the surface. Submerse your sensor in the ice water, ensuring it does not touch the container. Wait 5 minutes for the temperature to stabilize in the container and then once the sensor readings have stabilized for approximately 30 seconds (readings remain consistent), record the value as the measured_low_point

In order to obtain the measured_high_point, bring a pot of water to a rapid boil. Place your sensor in the boiling water, ensuring that it does not touch the pot. Allow the sensor to come up to temperature and once it has stabilized for approximately 30 seconds (readings remain consistent), record the value as the measured_high_point

Generally speaking, the reference_low_point should be left at 0.0 unless you have some special situation that changes the melting point of water. Because melting does not involve a gaseous phase change, the effects of air pressure and altitude on the melting point are minimal.

The reference_high_point on the other hand is greatly impacted by air pressure (and thus altitude). For example, the boiling point of water is 100.0C at sea level, and is approximately 72C at the summit of Mount Everest (8848m above sea level). While air pressure is what actually dictates boiling point, generally speaking altitude is a close enough approximation for most use cases. Engineering Toolbox has a page that gives you the boiling point of water at different altitudes.

This method is derived from this Instructable.

from w1thermsensor.calibration_data import CalibrationData
from w1thermsensor import W1ThermSensor, Unit

calibration_data = CalibrationData(
        measured_high_point=measured_high_point,
        measured_low_point=measured_low_point,
        reference_high_point=reference_high_point,
        reference_low_point=reference_low_point, # optional, defaults to 0.0
    )
sensor = W1ThermSensor(calibration_data=calibration_data)

corrected_temperature_in_celsius = sensor.get_corrected_temperature()
corrected_temperature_in_fahrenheit = sensor.get_corrected_temperature(Unit.DEGREES_F)
corrected_temperature_in_all_units = sensor.get_corrected_temperatures([
    Unit.DEGREES_C,
    Unit.DEGREES_F,
    Unit.KELVIN])

Async Interface

The w1thermsensor package implements an async interface AsyncW1ThermSensor for asyncio.

The following methods are supported:

• get_temperature()
• get_temperatures()
• get_resolution()

For example:

from w1thermsensor import AsyncW1ThermSensor, Unit

sensor = AsyncW1ThermSensor()
temperature_in_celsius = await sensor.get_temperature()
temperature_in_fahrenheit = await sensor.get_temperature(Unit.DEGREES_F)
temperature_in_all_units = await sensor.get_temperatures([
    Unit.DEGREES_C,
    Unit.DEGREES_F,
    Unit.KELVIN])

Usage as CLI tool

The w1thermsensor module can be used as CLI tool since version 0.3.0.
Please note that the CLI tool will only get installed with the Raspbian Python 3 package (sudo apt-get install python3-w1thermsensor)

List sensors

List all available sensors:

$ w1thermsensor ls
$ w1thermsensor ls --json  # show results in JSON format

List only sensors of a specific type:

$ w1thermsensor ls --type DS1822
$ w1thermsensor ls --type DS1822 --type MAX31850K  # specify multiple sensor types
$ w1thermsensor ls --type DS1822 --json  # show results in JSON format

Show temperatures

Show temperature of all available sensors: (Same synopsis as ls)

$ w1thermsensor all --type DS1822
$ w1thermsensor all --type DS1822 --type MAX31850K  # specify multiple sensor types
$ w1thermsensor all --type DS1822 --json  # show results in JSON format

Show temperature of a single sensor:

$ w1thermsensor get 1  # 1 is the id obtained by the ls command
$ w1thermsensor get --hwid 00000588806a --type DS18B20
$ w1thermsensor get 1  # show results in JSON format

Show temperature of a single sensor in the given resolution

$ w1thermsensor get 1 --resolution 10
$ w1thermsensor get --hwid 00000588806a --type DS18B20 --resolution 11

Change temperature read resolution and write to EEPROM

# w1thermsensor resolution 10 1
# w1thermsensor resolution --hwid 00000588806a --type DS18B20 11

Note: this requires root privileges

Contribution

I'm happy about all types of contributions to this project! :beers:

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This project is published under MIT.
A Timo Furrer project.
- :tada: -