Air quality monitoring

This projects aims to create an air quality monitoring setup with inexpensive components. Initially setup with an Arduino nano but later ported to a Raspberry PI.

The data is collected using the following sensors:

• BMP180 (Air pressure, Temperature)
• MH-Z19B (Co2 concentration)
• SMT20 (Humidity, Temperature) To interface with the sensors, either an Arduino or Raspberry PI computer can be used

Project Structure

Folder	Description	Remarks
Fritzing	The Fritzing projcet	Get fritzing here:https://fritzing.org/home/
additional	Datasets for the sensors
arduino	Ardunio libraries and source code.	This is a platfrom-io project. More info https://platformio.org/
grafana	Just the exported grafana dashboard
pi	This project implemented on a Raspberry PI
python	Python files: Write data values to the influx db (data_logger.py) and scan for new advertisement packets (scanner.py)	There is requirements.txt file present, which use to install all required packages: pip install -i requirements.txt

Technology Stack

• Data is stored in a Influx-DB
• A Grafana-Dashboard is used to display the measured values
• Scripting language at the receiver-side is Python 3.6
• (Arduino) The data is transmitted using iBeacon UUID-String (yes this is a hack see more info below)

Data transmission (Arduino)

As mentioned above the collected data is transmitted using Bluetooth Low Energy to the receiver. Generally speaking, the data is transmitted using the advertisement data:

Index         :        7   11 13   15     19 21   23 25                  39
                       |    |  |    |      |  |    |  |                   |
Example string: 4c000215 0190 1b   27   03c9 27   a0 a0   0000000 000000 2d       ffe0ffe1 c5
Labels        : Ibeacon  co2  temp.temp pres.pres hum.hum ------- ------ checksum other_stuff

However, since the HM-10 does not support changing the advertisement data directly, I had to abuse the iBeacon mode where you can change 32 Bytes of the UUID-String. To make things worse (more interesting!), the BLE-Module only allows you to change 8 Bytes of the UUID-String at once. For example the AT command for the first 8 Bytes:

AT+IBE0AABBCCDD # As a side-note: all Hex-Characters have to be upper-case

And you guessed it, you can't control when an advertisement package is sent. This the reason the checksum is needed :)

Future work, remarks and problems

• Currently only one temperature value is evaluated. However, all sensors measure temperature, therefore we could compare them and even create some sort of a confidence-interval
• If you power on the whole circuit, the first valid (according to the checksum) transmitted value of the co2-sensor is sometimes way off (in the 5-6k area)
• Don't buy the components on aliexpres or similar. I've wasted (too) many hours figuring out that for example the HM-10 Module was a clone of a clone of the original.
• Feedback, ideas and PR's welcome :)