Weather HAT Python Library & Examples

Pre-requisites

You must enable:

• i2c: sudo raspi-config nonint do_i2c 0
• spi: sudo raspi-config nonint do_spi 0

You can optionally run sudo raspi-config or the graphical Raspberry Pi Configuration UI to enable interfaces.

Installing

Stable library from PyPi:

• Just run pip3 install weatherhat

In some cases you may need to use sudo or install pip with: sudo apt install python3-pip

Latest/development library from GitHub:

• git clone https://github.com/pimoroni/weatherhat-python
• cd weatherhat-python
• sudo ./install.sh

Some of the examples use additional libraries. You can install them with:

pip3 install fonts font-manrope pyyaml adafruit-io

Using The Library

Import the weatherhat module and create an instance of the WeatherHAT class.

import weatherhat

sensor = weatherhat.WeatherHAT()

Weather HAT updates the sensors when you call update(interval=5).

Temperature, pressure, humidity, light and wind direction are updated continuously.

Rain and Wind measurements are measured over an interval period. Weather HAT will count ticks of the rain gauge and (half) rotations of the anemometer, calculate rain/wind every interval seconds and reset the counts for the next pass.

For example the following code will update rain/wind speed every 5 seconds, and all other readings will be updated on demand:

import time
import weatherhat

sensor = weatherhat.WeatherHAT()

while True:
    sensor.update(interval=5.0)
    time.sleep(1.0)

Averaging Readings

The Weather HAT library supplies set of "history" classes intended to save readings over a period of time and provide access to things like minimum, maximum and average values with unit conversions.

For example WindSpeedHistory allows you to store wind readings and retrieve them in mp/h or km/h, in addition to determining the "gust" (maximum wind speed) in a given period of time:

import time
import weatherhat
from weatherhat.history import WindSpeedHistory

sensor = weatherhat.WeatherHAT()
wind_speed_history = WindSpeedHistory()

while True:
    sensor.update(interval=5.0)
    if sensor.updated_wind_rain:
        wind_speed_history.append(sensor.wind_speed)
        print(f"Average wind speed: {wind_speed_history.average_mph()}mph")
        print(f"Wind gust: {wind_speed_history.gust_mph()}mph")
    time.sleep(1.0)

Quick Reference

Temperature

Temperature readings are given as degrees celsius and are measured from the Weather HAT's onboard BME280.

Device Temperature

sensor.device_temperature

Device temperature in degrees celsius.

This is the temperature read directly from the BME280 onboard Weather HAT. It's not compensated and tends to read slightly higher than ambient due to heat from the Pi.

Compensated (Air) Temperature

sensor.temperature

Temperature in degrees celsius.

This is the temperature once an offset has been applied. This offset is fixed, and taken from sensor.temperature_offset.

Pressure

sensor.pressure

Pressure in hectopascals.

Humidity

sensor.humidity

Humidity in %.

Relative Humidity

sensor.relative_humidity

Relative humidity in %.

Relative humidity is the water content of the air compensated for temperature, since warmer air can hold more water.

It's expressed as a percentage from 0 (no moisture) to 100 (fully saturated).

Dew Point

sensor.dewpoint

Dew point in degrees celsius.

Dew point is the temperature at which water - at the current humidity - will condense out of the air.

Light / Lux

sensor.lux

Light is given in lux.

Lux ranges from 0 (complete darkness) to.

Wind

Both wind and rain are updated on an interval, rather than on-demand.

To see if an update() call has resulted in new wind/rain measurements, check:

sensor.updated_wind_rain

Wind Direction

sensor.wind_direction

Wind direction in degrees.

Wind direction is measured using a potentiometer and uses an analog reading internally. This is converted to degrees for convenience, and will snap to the nearest 45-degree increment with 0 degrees indicating North.

Wind Speed

sensor.wind_speed

Wind speed in meters per second.

Weather HAT counts every half rotation and converts this to cm/s using the anemometer circumference and factor.

It's updated depending on the update interval requested.

Rain

sensor.rain

Rain amount in millimeters per second.

Weather HAT counts every "tick" of the rain gauge (roughly .28mm) over the given update internal and converts this into mm/sec.

Total Rain

sensor.rain_total

Total rain amount in millimeters for the current update period.

Changelog

0.0.1

• Initial Release