The winters in Germany's Sauerland region are long, but above all, changeable. Sometimes it snows in October, and sometimes you experience a spring-like 15°C (59°F) over Christmas. The beekeepers in the area are prepared for this and prepare their bees for the winter in the early autumn after the last honey harvest by feeding several liters of sugar solution into the hives, depending on the size of the bee colony. When the outside temperatures drop, the response is prompt: Lock up, install mouse gratings in front of the entrance, and meet again in April.

Because beekeepers do not normally open the hives during the winter months, they cannot know if the population is thriving. Inspired by the Hiveeyes Project [1] and the Open Hive Monitoring System [2], we planned our own monitoring solution for our colonies. As hobby beekeepers, we first want to observe the temperature (see the "Test Setup" box) but, later, also connect our own hive scale.

Connecting the DHT11 Sensor

The DHT11 digital temperature and humidity sensor is available for a few dollars. It supplies the temperature in degrees Celsius and the relative humidity as a percentage. In the first trial, we connected the sensor directly to the RPi2B. The Python_DHT sensor library [3] helps with the readout. After installing the packages build-essential and python3-dev, we checked out the sensor library from the GitHub repository and installed it on the computer:

$ git clone https://github.com/jugend-programmiert/Python_DHT
$ cd Python_DHT
$ sudo python3 setup.py install

To use the library in your own Python scripts, you use import. For example, Listing 1 reads sensor data and outputs it to the console. A test run on the console shows that the sensor and RPi2B are working together:

01 import Python_DHT
02
03 sensor = Python_DHT.DHT11
04 pin = 4
05 humidity, temperature = Python_DHT.read_retry(sensor, pin)
06 print("dht temperature="+str(temperature)+",humidity="+str(humidity))

$ python3 dht11_simple.py
dht temperature=17.0,humidity=49.0

After saving the script to /usr/local/bin, the database and the collector were the next steps.

Setting Up the Database

The InfluxData package source [4] contributes both the InfluxDB database [5] and the Telegraf collector [6], which are added to /etc/apt/sources.list.d/influxdb.list; then, we added the repository's GnuPG key:

$ curl -sL   https://repos.influxdata.com/influxdb.key | sudo apt-key add -

After updating the package list (apt update) and importing the influxdb and telegraf packages, we configured the database to start automatically at boot time, initialized the server, and started the command-line client:

$ sudo systemctl enable influxdb
$ sudo systemctl start influxdb
$ sudo influx
Connected to http://localhost:8086 version 1.5.1
InfluxDB shell version: 1.5.1

When the client started, we created a new admin account and a new database named telegraf:

> CREATE USER admin WITH PASSWORD '****' WITH ALL PRIVILEGES
> CREATE DATABASE telegraf
> exit

In the InfluxDB configuration file /etc/influxdb/influxdb.conf, you need to enable the web server under [http]:

[http]
  enabled = true
  bind-address = ":8086"

After restarting the service by typing

systemctl restart influxdb

the Telegraf configuration continues.

Well Acquired

The telegraf account must be a member of the gpio group for the collector to read values from the GPIO pin:

usermod -a -G gpio telegraf

The /etc/telegraf/telegraf.conf file contains the database information in the OUTPUT PLUGINS section:

[[outputs.influxdb]]
  timeout = "5s"
  username = "admin"
  password = "****"

The INPUT PLUGINS area also has a space for your Python script, which will run once a minute:

[[inputs.exec]]
    commands = ["python3 /usr/local/bin/dht11_simple.py"]
    interval ="60s"
    data_format = "influx"

If you want to check whether the communication between Telegraf and InfluxDB is working, you can launch the influx client. Listing 2 shows how we query the telegraf database on the test system.

$ influx
Connected to http://localhost:8086 version 1.5.1
InfluxDB shell version: 1.5.1
> show databases
name: databases
name
----
telegraf
_internal
> use telegraf
Using database telegraf
> show series
key
---
cpu,cpu=cpu-total,host=raspberrypi
[...]
dht,host=raspberrypi
[...]
system,host=raspberrypi
> select * from dht;
name: dht
time                host        humidity temperature
---------------------------
1522242851000000000 raspberrypi 54       19
1522242911000000000 raspberrypi 54       19
1522242971000000000 raspberrypi 53       19
1522243031000000000 raspberrypi 53       19
[...]