The MagPi - July 2018

raspberrypi.org/magpi May 2018 77

BUILD A WEATHER STATION Feature

raspberrypi.org/magpi 77

TIP THE BUCKET

The product data sheet (magpi.cc/ltofJB)
tells us that 0.2794 mm of rain will tip
the bucket. You can multiply this by the
number of tips to calculate the amount of
rainfall. If you’re using a different type
of rain gauge, then you should consult
the relevant data sheet or determine the
volume of water required experimentally.

STEP 2

INSIDE THE BUCKET
The top of the back wall does come off if
you want to see inside; just pull on the
flat end gently and it should release.
Inside there’s a small circuit board
that you can remove to examine. In the
middle of it you will see the reed switch.
Replace the circuit board and back wall lid
before continuing.
When one of the buckets tips, the
magnet passes the reed switch, causing
it to close momentarily. So, just like with
the anemometer, if you connect the rain
gauge to a GPIO pin on the Raspberry Pi,
you can treat it like a button and count the
number of ‘presses’ to calculate rainfall.

STEP 3

WIRE IT UP
To test the rain gauge, you’ll need to
either remove the RJ11 connector and
strip the wires, or make use of an RJ11
breakout board.
The Oracle Weather Station rain
gauge is connected to GPIO 06,
so for consistency, use the same
pin for your device. (See the
main Figure 1 circuit diagram on
page 72.)

STEP 4

WRITE THE CODE

Using the code you wrote for the
anemometer as a starting point,
write a program called rainfall.py
(saved in the /home/pi/weather-
station directory) to detect when

STEP 1

One of the best ways to store

your weather data is in a

database. Databases can store

very large numbers of records

efficiently and make it easier

to sort, search, and analyse

your data.

There are many different

pieces of database software,

and MariaDB is a good, versatile

general-purpose product. You

should have already installed

it – if not, head back to the

‘Software download’ section on

page 71 and install it.

Now follow the instructions at

magpi.cc/ltofJB to learn how to

set up and run your database.

July 2018

from gpiozero import Button

rain_sensor = Button( 6 )

BUCKET_SIZE = 0.2794

count = 0

def bucket_tipped():

global count

count = count + 1

print (count * BUCKET_SIZE)

def reset_rainfall():

global count

count = 0

rain_sensor.when_pressed =

bucket_tipped

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rainfall.py

CODE

Language: Python

Name: rainfall.py

magpi.cc/uNgWwe

the rain gauge bucket has tipped. It should

print out a running count of how many

bucket tips have occurred.

Now that you can count bucket tips,

you need to convert this into a height of

water that equals the amount of rain that

has fallen.

Finally, we use a function named

reset_rainfall to reset the count of

bucket tips so that it starts at 0 again.

You will need this function for your fully

operational weather station.