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The Datenzwerg#

What is the Datenzwerg?#

The Datenzwerg is a garden gnome with a mission: To collect environmental data and make it publicly available.

It was originally developed for the Chaos Communication Camp 2023 where we (@romses and @foosel) deployed a small army of 10 Datenzwerge across the camp grounds: Happy, Doc, Grumpy, Dopey, Bashful, Sleepy, Sneezy, Nerdy, Kinky and Hefty1.

The Datenzwerge also made a reappearance at the 37c3 and if all goes to plan a small army of them will also be attending GPN22.

The Datenzwerg consists of a 3D printed gnome body, a custom PCB with an ESP8266 D1 Mini microcontroller board, a BME280, SGP30, UV and sound sensor and an optional 18650 battery. It's powered by ESPHome and sends its data to an InfluxDB instance. The firmware currently logs temperature, relative and absolute humidity, air pressure, dew point, UV index, eCO2, TVOC and sound pressure.

We asked ChatGPT to describe the Datenzwerg for us2 and this is what it came up with:

Welcome to the world of the Datenzwerg, an enchanting garden gnome with a technological twist! This delightful little creature may look like your average garden decoration, but it harbors a secret mission that is as intriguing as it is important. The Datenzwerg is on a quest to collect environmental data and make it publicly available for the benefit of all.

[...]

By leveraging its unique vantage point in gardens and outdoor spaces, the Datenzwerg provides an unparalleled perspective on the environment around us.

All the data collected by these pint-sized environmental guardians is made freely available to the public through an intuitive online platform.

[...]

At the upcoming Chaos Communication Camp, we are excited to introduce the Data Gnome to a wider audience of tech enthusiasts, hackers, and environmental advocates. This extraordinary convergence of nature and technology showcases the potential for citizen-driven environmental monitoring.

A short history of the Datenzwerg#

2023-06-11
The idea of the Datenzwerg is born at the final day of GPN21, just before a joint bar shift by @romses and @foosel. Slow parts of the shift as well as the drive back to the Rhein-Main-Area are spent discussing the idea. Romses registers a domain name.
2023-06-30
romses and foosel meet up for a joint tinkering session. The first two mainboards are built. The Datenzwerg is alive!
2023-07-08
Another joint tinkering session takes place. Another 8 mainboards are built. The Datenzwerg army is growing!
2023-07-19
After finalizing the model and followed by 60+ hours of collective print time, all 10 Datenzwerg bodies are printed.
2023-07-23
The basic infrastructure goes live. Sensors start to report to the official servers at datagnome.de.
All Datenzwerg bodies are prepared for getting their electronics installed: Magnets are glued in, the UV transmissive discs are installed and any holes filled with milliput.
2023-07-24
The firmware reaches a first feature complete state.
2023-07-28
All Datenzwerge are now in their bodies and are happily sending data.
2023-08-04
The website reaches a first complete state in both German and English.
2023-08-09
The sensor data is publicly available via InfluxDB and MQTT.
The firmware sees final adjustments in preparation for the Camp.
2023-08-11
The Datenzwerge are offline again, temporarily. Next stop: CCCamp!
2023-08-15 - 2023-08-19
Datenzwerg deployment at CCCamp23.
2023-08-19
(Almost) all Datenzwerge have left the camp and are traveling back to the Rhein-Main-Area. Thanks everyone for the big interest!
2023-08-22
The Datenzwerge are back home and are being prepared for future deployments. The CCCamp data export is available in the repository.
2023-08-28
The infrastructure has been shut down for now and only the page here and of course the source code remains. The Datenzwerge are taking a well deserved rest.
2023-10-31
Work has started on the 37c3 edition of the Datenzwerg. The plan is to add TVOC monitoring to the sensor suite. A new PCB has been designed, ordered, arrived, and ten new mainboards have been soldered.
2023-12-08
An alternative version of the bottom part of the Datenzwerg is finished that allows leading through a cable. Ten new bottoms have been printed and magnetised to allow for USB or POE powering at 37c3. This completes the hardware side of the 37c3 preparations.
2023-12-11
The server infrastructure is back up an running and the first Datenzwerge are reporting data again.
2023-12-26 2023-12-30
The Datenzwerge are deployed at 37c3.

FAQ#

What kind of data does the Datenzwerg collect?#

The Datenzwerg contains sensors to collect the following data:

  • Temperature
  • Relative humidity
  • Air pressure
  • eCO2
  • TVOC
  • UV sensor voltage
  • Microphone voltage
  • Battery voltage
  • WiFi signal strength

We calculate dew point and absolute humidity from the temperature and relative humidity values, UV index from the UV sensor's voltage and sound pressure (noise level) from the microphone voltage. The calculations are done in firmware.

Do you record audio?#

No. While there is a microphone inside each Datenzwerg hooked up to the ESP's ADC, we only use it to sample 1s of audio every 5s, from which we calculate the peak-to-peak voltage and from that the sound pressure on the Datenzwerg itself. The sample rate is way too low and irregular to record any meaningful audio, and the noise on the line vs the 10-bit ADC would make for a bad experience as well if that was our intention. We are not interested in audio, we are interested in noise levels.

What's the battery life?#

In our tests, a Datenzwerg without TVOC sensor seems to last between three to four days on a single charge of our 18650 LiPos that range from 1600mAh to 2800 mAh. This obviously depends on the cell capacity but also temperature and other environmental factors.

With the TVOC sensor included powering via a single 18650 LiPo is sadly not working out.

Why are the measured temperatures that high during the day?#

We need to put the gnomes into direct sunlight in order to be able to measure UV index. Additionally, the ESP and now also the TVOC sensor are producing heat themselves. We tried to get enough airflow inside the gnome body, but sadly the material itself radiates off heat a lot. As such, the temperature readings are distorted, especially under direct sun light.

Where can I find the data?#

Each Datenzwerg sends its data to a central self-hosted InfluxDB instance. The data is then visualized using Grafana.

Some of those visualisations as well as credentials for accessing the raw data and links to data exports from past events can be found here.

Where can I find the source?#

Everything can be found in this GitHub repository: romses/Datenzwerg.

Media echo#

  • The datagnomes were the opener at the #cccamp23 review media.ccc.de.
  • romses and foosel were guests at the Datenleben Podcast and talked about the Datenzwerge (German).

Credits & Thanks#

The Datenzwerg was created by @romses and @foosel.

The Datenzwerg logo was created by D.B.

The Datenzwerg model files are based on this "Garden Gnome" model by Sci3D, released under CC-BY. Our remix can be found here and of course also in the GitHub repository.

The SCD41 sensors were sponsored by @dx@mastodon.social.

  1. Yes, the last three are not canon, and one of them even is a smurf - so what, chaos ftw! ↩

  2. Prompt: 'Write me a text for a website that gives an overview of the "Datenzwerg". The Datenzwerg is a garden gnome that collects environmental data, and makes it publicly available. The Datenzwerg will be presented at the Chaos Communication Camp.' ↩