LoraWanDustSensor

Project LoRaWAN dust Sensor
LoRaWAN airborne particulate matter sensor
Status	In progress
Contact	bertrik
Last Update	2019-04-06

The plan

The plan is to create a system consisting of:

• a sensor that measures airborne particulate matter and sends the measurement data using LoRa/TheThingsNetwork to a central location.
• a backend that collects the data from TTN and forwards it to luftdaten.info

This has been done before by other people, but can't find any really good examples:

• source code location is obscure, I will publish all source code on github and put up documentation on this wiki
• payload format is non-standard, I'd like to use something relatively universal and standard, so I think I will try to use the Cayenne LPP format.

This has been done by TTN Ulm, see https://github.com/verschwoerhaus/ttn-ulm-feinstaub (the sensor code) and https://github.com/verschwoerhaus/ttn-ulm-muecke (the forwarder, in python)

Sensors join the network using OTAA (instead of ABP), that way I try to minimize the setup of each individual node.

So I'd like to just re-invent the wheel properly this time.

Next

• Figure out which pins are used by Luftdaten on ESP32 and copy that.

Hardware

The node is based on Arduino. The sensor will be an SDS-011, just like in the luftdaten project.

Page with correct pinout.

I will take a glance at how this sensor is being "driven" in this project, e.g. typical on-off times, averaging, etc.

• 145 second cycle time

To do the LoRa stuff, I will probably use an ESP32 with an RFM95 built in. The ESP32 is already very similar to the ESP8266 currently used in the luftdaten project.

Software

Source code can be found on the github page.

Common

Packet format

Packets transferred over LoRa contain:

• structure version id: 2 bytes
• id for forwarding towards luftdaten (esp-XXXX number): 6 bytes
• PM10 value, probably encoded in units of 0.1 ug/m3: 2 bytes
• PM2.5 value, probably encoded in units of 0.1 ug/m3: 2 bytes
• temperature, encoded in units of 0.1 deg C: 2 bytes
• pressure, encoded in units of 0.1 hPa, 2 bytes
• relative humidity, encoded in units of 0.1%, 2 bytes

Total: 18 bytes

Not present value is 0xFFFF. Encoding is big endian.

Would be nice to use Cayenne for this, but I don't know if Cayenne has an id for particulate matter.

Node

To compile the code, platformio is used, probably with the following libraries:

• https://github.com/fcgdam/TTGO_LoRa32
• LMIC

Data forwarding

I will use a Java program to subscribe to this MQTT stream, decode the telemetry packets and forward them to luftdaten. There is no storage of measurement data in the Java application.

I've already developed some Java code that publishes the measurement values towards luftdaten.info. Also I've developed code before to subscribe to the TTN MQTT stream.