what & why?

Indoor measuring of Co2 and Temperature

Especially in office environments employees are sensitive to high levels of Co2 and/or uncomfortably with hot office temperatures. This project consists of two parts, the monitor.py and the webinterface.

monitor.py to read the data from the TFA-Dostmann AirControl Mini CO2 sensor and generating the graphs
webinterface to display the graphs

Example Screenshot

requirements

hardware

TFA-Dostmann AirControl Mini CO2 Messgerät -- 80 euro
Raspberry PI 2 Model B -- 40 euro
case, 5v power supply, microSD card

software

Download Raspbian and install it on the microSD.

installation on the raspberry

Boot the raspberry with the raspbian and configure according to your needs.

At the moment, monitor.py renders the graphs to /var/www/html/images, and creates the RRD database in /var/local/monitor/co2-temp.rrd.

To change this, change the variables RRDDB_LOC and GRAPHOUT_DIR in monitor.py.

monitor.py should not run as root, so we create a service user (the group for this user is created automatically by adduser):

sudo adduser --home /var/local/monitor --shell /usr/sbin/nologin --disabled-password monitor

install software

Other than Wooga this setup generates and serves the graphs locally, thus the following components are needed:

sudo apt-get install rrdtool python-rrdtool nginx ntp
cp /usr/share/zoneinfo/Europe/Vienna /etc/localtime                             

systemctl enable nginx                                                                                                                                        
systemctl start nginx

systemctl enable ntp                                                            
systemctl start ntp

Copy monitor.py and the webinterface to their location:

sudo cp monitor.py /usr/bin
sudo mv /var/www/html/index.html /var/www/html/index.nginx-debian.html
sudo rsync -av --progress web/* /var/www/html
sudo mkdir /var/www/html/images
sudo chown -R monitor: /var/www/html/images

fix socket permissions

The python script reading the sensor should not run as root, so the device permissions need to be set accordingly.

For a non-permanent fix run as root:

sudo chmod a+rw /dev/hidraw0

The better way to deal with this situation is to set the permissions using udev rules.

We want to set only the really needed permissions on the device, therefor the udev-rule should only apply to the specific device, or product which is announced by the device when USB initializes it.

To get the product name the bus and device id from lsusb is needed:

lsusb
Bus 001 Device 004: ID 04d9:a052 Holtek Semiconductor, Inc.

With this information the product name can be read from udevadm, using the bus id 001 and the device id 004 like this:

udevadm info -a -p $(udevadm info -q path -n /dev/bus/usb/001/004) | grep product
    ATTR{product}=="USB-zyTemp"

The product name is in this case USB-zyTemp which can be used in the udev rule:

echo 'ACTION=="add", SUBSYSTEMS=="usb", ATTRS{product}=="USB-zyTemp", MODE="0664", GROUP="monitor"' > /etc/udev/rules.d/40-hidrwaw.rules

After plugging the TFA device in, at least one device file (e.g. /dev/hidraw0) should be generated with the correct permissions.

run the script

monitor.py can be tested by invoking:

sudo -u monitor monitor.py /dev/hidraw0

We need to run it as monitor user because by default RRD databse is located in the folder where only monitor user has access to and access to a socket was granted to monitor group.

run on startup

monitor.py can safely be called via a cronjob; it will exit if another instance is already running.

The cronjob can be added to /etc/crontab like this:

*/3 *   * * *   monitor /usr/bin/monitor.py /dev/hidraw0

todo

configure RRD database location and graph directory
mobile webinterface navigation
configuring webinterface strings
notification via email

credits

based on Wooga Office Weather

license

MIT

willemsk/officeweather