Tracer Release

Indoor Air and Climate Change (2015-2017)

Carbon dioxide (CO2) tracer injection/detection for time-resolved indoor air ventilation rates. Parts include:

• CO2 analyzer (LI-840A; LICOR Biosciences) and accessories (e.g. pump, power supply, filters, etc)
• Volumetric mass flow controller (0-20 sLPM; Alicat Scientific) and cable for 8-pin interface
• Linux computer (Raspberry Pi B+) plus
  • Paired Bluetooth serial dongles (for CO2 analyzer)
  • USB-serial adapter (for flow controller)
• Enclosure plus cable grommets, hardware, etc

Usage

TODO

Initial Setup

OS Prep

The base distribution is Raspbian Lite (Feb 2016 as I write this). Use sudo raspi-config to:

• expand file system
• change the password
• set internationalization options to your preference; we use
  • US locale & keyboard setup
  • year-round Pacific Standard Time (GMT+8)
• advanced options
  • change the hostname
  • enable SSH (if you use it; you should be using it)

Reboot after exiting then run a complete update:

pi@tracer:~ $ sudo apt-get update && sudo apt-get dist-upgrade -y

And install some basic programs:

pi@tracer:~ $ sudo apt-get install git tmux

Now is a good time eliminate tabs. Create the file ~/.nanorc:

set tabsize 4
set tabstospaces

Hardware setup

The mass flow controller is connected to the Raspberry Pi using a USB serial (RS-232) adapter. The CO2/H2O analyzer is connected to the Pi using paired Bluetooth serial dongles (HC-05).

In the previous release, we created udev rules to assign device names to the USB serial adapters based on their physical USB port. This was only required because (1) we used two identical adapters and (2) the specific adapters we bought are relatively poor quality (they do not possess unique serial numbers).

Going forward, the analyzer is connected using paired Bluetooth serial modules. Since the modules are 3.3V logic, the receiving module is directly connected to the Pi's hardware UART and there is no need to assign names based on physical USB port.

Here's our rules file, /etc/udev/rules.d/98-tracer-release.rules:

KERNEL=="ttyUSB0", SYMLINK+="mfc"
KERNEL=="ttyAMA0", SYMLINK+="co2" 

Reboot for rules to take effect. YMMV with other brands of USB serial adapters.

Software packages

Install python support for the serial ports:

pi@tracer:~ $ sudo apt-get install python-serial

Share data

First, create shared data directories for LI840A

• sudo mkdir /var/log/li840a
• sudo mkdir -p /var/log/li840a/raw (XML data stream TODO)
• sudo mkdir -p /var/log/li840a/1hz ("raw" but in TSV)
  • TODO: `.../1min', mean 1-minute values
  • TODO: .../30min, mean/sdev/min/max half-hour values
  • TODO: .../daily, mean/sdev/min/max daily values
• sudo mkdir /var/log/tracer
• sudo ln -s /var/log/li840a /var/log/tracer/sample
• sudo ln -s /var/log/mfc /var/log/tracer/inject

Now export

• Install samba: sudo apt-get install samba -y
• Modify samba config: sudo nano /etc/samba/smb.conf
  • comment out default exports (home, printers)
  • add following:

...
unix extensions = no

[data]
   browseable = yes
   comment = Data directory
   create mask = 0700
   directory mask = 0700
   only guest = yes
   path = /var/log/tracer
   public = yes
   read only = yes
   follow symlinks = yes
   wide links = yes

Setup wifi connection

Before connecting wifi adapter, add the following block to /etc/wpa_supplicant/wpa_supplicant.conf:

network={
  ssid="<the SSID we use>"
  psk="<the long password we use>"
}

Install scripts as services

Copy the scripts to appropriate directory (per the Linux Filesystem Hierarchy Standard) and drop file extensions. Then make the files executable.

pi@tracer:~/2015-iaq-tracer $ sudo cp scripts/co2-logger.py /usr/sbin/co2-logger
pi@tracer:~/2015-iaq-tracer $ sudo cp scripts/mfc-control.py /usr/bin/mfc-control
pi@tracer:~/2015-iaq-tracer $ sudo chmod +x /usr/sbin/co2-logger
pi@tracer:~/2015-iaq-tracer $ sudo chmod +x /usr/bin/mfc-control

Now install and enable the co2 logging service:

pi@tracer:~/2015-iaq-tracer $ sudo cp etc/systemd/system/co2-logger.service /etc/systemd/system/
pi@tracer:~/2015-iaq-tracer $ sudo systemctl enable co2-logger.service

And finally, setup the mass flow controller script on a timer:

pi@tracer:~ $ sudo crontab -e

...
0 */3 * * * /usr/bin/mfc-control

This would run the script every 3 hours, at the start (zeroth minute) of the hour.

Report data to ScadaBR

Run the file scripts/update-scadabr.py every minute using cron:

$ sudo crontab -e

...
* * * * * python /full/path/to/the/script

Configure serial console for bluetooth dongles

Ignore this section:

In previous release, a Bluetooth serial adapter was used to provide shell access via the hardware UART (/ttyAMA0). That access route has been shelved so the UART can be used with paired Bluetooth serial modules to wirelessly record the CO2/H2O analyzer.

We've selected an HC-06 module (linvor1.8) which, unfortunately, cannot operate above 38400 baud rate. The default serial UART is 115200 so it must be changed.

First, re-enable serial console output via raspi-config, if req'd. Then change instances of '115200' to '19200' in /boot/cmdline.txt.

Since Raspbian Jessie uses systemd, there is no /etc/inittab file.

https://learn.adafruit.com/adafruit-ultimate-gps-hat-for-raspberry-pi/pi-setup http://blog.miguelgrinberg.com/post/a-cheap-bluetooth-serial-port-for-your-raspberry-pi