Sensor-data-bridge

Project LoraLuftdatenForwarder
LoRaWAN forwarder for particulate matter data
Status	In progress
Contact	bertrik
Last Update	2021-06-07

What is this

This is a companion project of LoraWanDustSensor.

It takes airborne particulate matter measurement data transferred through TheThingsNetwork and forwards it to online databases:

• http://sensor.community (formerly Luftdaten),
• http://opensensemap.org and
• https://cayenne.mydevices.com

Project on Github: https://github.com/bertrik/LoraLuftdatenForwarder

Features

• Picks up particulate matter measurement data received through TheThingsNetwork, using their "v3" infrastructure
• Forwards measurement data to https://sensor.community
• Forwards measurement data to https://opensensemap.org, you can configure the opensense-id by adding a device attribute in TheThingsNetwork console
• Forwards measurement data to https://cayenne.mydevices.com, you configure the username/password/clientid by adding a device attribute in TheThingsNetwork console
• Supports Cayenne payload format for the data encoding
• Handles particulate matter data (PM10, PM4.0, PM2.5, PM1.0), temperature, humidity, barometric pressure
• Can be run as a systemd service, so it automatically restarts in case the software would crash

Next steps

• add support for NB-IOT modem with t-mobile backend, see my Sim7020 project
• add support for other backends, e.g. feinstaub-app?

Requirements

You need the following:

• a server that is always on and connected to the internet, can be Linux or Windows
• a Java installation (JDK to compile), at least version 8
• some configuration on TheThingsNetwork side
• some configuration of my application (YAML file)

Compilation

To compile the software:

• clone the software from my github archive

 git clone https://github.com/bertrik/LoraLuftdatenForwarder.git

• enter the LoraLuftdatenForwarder/gradle directory

 cd LoraLuftdatenForwarder/gradle

• run the gradle script to build the software (Linux):

 ./gradlew assemble

or (Windows):

 gradlew assemble

• the application zip & tar is now available in LoraLuftdatenForwarder/LoraLuftdatenForwarder/build/distributions

To update to the latest version:

• Update software from github archive:

 git pull

• perform the last two steps above again

Installation

Unzip the distribution file somewhere on your system. I put it in my home directory, for example

 cd
 tar xvf code/LoraLuftdatenForwarder/LoraLuftdatenForwarder/build/distributions/LoraLuftdatenForwarder.tar

Configuration

Node configuration

The particulate matter measurement device needs to send data in the Cayenne format. I used the following conventions:

• PM10 is encoded as analog value on channel 1
• PM2.5 is encoded as analog value on channel 2
• PM1.0 is encoded as analog value on channel 0 (optional)
• PM4.0 is encoded as analog value on channel 4 (optional)
• Temperature is encoded using standard Cayenne encoding (optional)
• Humidity is encoded using standard Cayenne encoding (optional)
• Barometric pressure is encoded using standard Cayenne encoding (optional)

TheThingsNetwork application/device configuration

TTN API key rights

You need to define an 'application' on TheTheThingsNetwork.

• Go the TTN console: https://console.cloud.thethings.network/ and log in
• You need an 'application', create a new one, or use an existing one
• Within the application you need a 'device', so create a new one, or use an existing one:
  • Use OTAA, LoRaMac version 1.0.3
  • Enter the device EUI as displayed on the display
  • Use the application keys as specified in my LoraWanDustSensor page
• You need an API key
  • Create this on the TTN console, grant individual rights as shown in the screenshot
  • NOTE: you have only one chance to copy this key somewhere, so copy/paste it locally to a text file or something

LoraLuftdatenForwarder configuration

To configure the application:

• Start the application without a configuration file, this will create a default template, stop the application again

 cd LoraLuftdatenForwarder
 bin/LoraLuftdatenForwarder
 (ctrl-C)

• Edit the loraluftdatenforwarder.yaml file, example:

---
ttn:
  mqtt_url: "tcp://eu1.cloud.thethings.network"
  identity_server_url: "https://eu1.cloud.thethings.network"
  identity_server_timeout: 20
  apps:
  - name: "particulatematter"
    key: "NNSXS......."
    encoding: "CAYENNE"
luftdaten:
  url: "https://api.sensor.community"
  timeout: 20
opensense:
  url: "https://api.opensensemap.org"
  timeout: 20

So:

• enter the name of your application
• enter the TTN API key you saved earlier
• other defaults are probably OK

Sensor.community

TODO

• Go to https://devices.sensor.community/ and log in
• Register a node with id 'TTN-<device-EUI-as-shown-on-display>' (without the spaces or hyphens, e.g. 'TTN-0000547AF1BF713C')
• Register it with the proper configuration, e.g. SDS011 with BME280

Opensensemap

• Go to opensensemap.org and log in
  • Create an opensense node with the proper configuration
  • Copy the opensensenmap 'box id', a long hexadecimal string
• Go the TTN console: https://console.cloud.thethings.network/ and log in
  • Add an attribute for the device, under 'General settings', name = 'opensense-id', value = boxid that you copied from opensensemap.org
• The mapping from TTN-id to boxid is refreshed by the forwarder once an hour, so within an hour the forwarding to opensensemap.org starts

Cayenne myDevices

• Go to https://cayenne.mydevices.com/ and log in
  • Add a new node, TODO
• Go to TTN console and log in
  • Add attributes for the device, under 'General settings'
    • attribute name = 'mydevices-username', value = MQTT username from cayenne mydevices dashboard
    • attribute name = 'mydevices-password', value = MQTT password from cayenne mydevices dashboard
    • attribute name = 'mydevices-clientid', value = Client ID from cayenne mydevices dashboard

Work in progress

SPS30 data

The SPS30 produces mass concentration data in 4 categories, particle count in 5 categories, plus particle size. It would be tricky to encode this in Cayenne, so this describes an alternative encoding:

Format:

• 16-bit (big endian) PM1.0 mass concentration (unit 0.1)
• 16-bit (big endian) PM2.5 mass concentration (unit 0.1)
• 16-bit (big endian) PM4.0 mass concentration (unit 0.1)
• 16-bit (big endian) PM10 mass concentration (unit 0.1)
• 16-bit (big endian) PM0.5 number concentration (unit 1)
• 16-bit (big endian) PM1.0 number concentration (unit 1)
• 16-bit (big endian) PM2.5 number concentration (unit 1)
• 16-bit (big endian) PM4.0 number concentration (unit 1)
• 16-bit (big endian) PM10 number concentration (unit 1)
• 16-bit (big endian) typical particle size (unit nm)

A total of 20 bytes. Temperature and humidity is not encoded.

Forwarding noise data

How it is encoded in the sensor.community firmware:

• Three values are sent in the JSON to sensor.community:
  • "noise_LAeq", value in dB(A), meaning?
  • "noise_LA_min", value in dB(A), some kind of minimum
  • "noise_LA_max", value in dB(A), some kind of maximum

I think these can be encoded in Cayenne as a simple analog value (which has a range of approximately -327..327 with a resolution of 0.01. Just need to assign a channel number to it.

Values are read from the noise sensor as follows:

• call to dnms_calculate_leq()
• call to dnms_read_data_ready(&data_ready) returns 0 if OK and (data_ready != 0)
• call to dnms_read_leq(&dnms_values) returns 0 if OK
• firmware applies a "correction" by adding a fixed offset

Measurement values are encoded as 32-bit units, interpreted as 32-bit floats.

References:

• DNMS is read at https://github.com/opendata-stuttgart/sensors-software/blob/beta/airrohr-firmware/airrohr-firmware.ino#L3392
• DNMS is formatted in the JSON at https://github.com/opendata-stuttgart/sensors-software/blob/beta/airrohr-firmware/airrohr-firmware.ino#L3405
• DNMS I2C code is at https://github.com/opendata-stuttgart/sensors-software/blob/beta/airrohr-firmware/dnms_i2c.cpp