Fixi v1

The Fixi v1 is a micro-sensor for the stationary measurement of suspended particles (or fine particles) in ambient air. The measurements are carried out continuously (one data every 140 seconds), which allows to know the variations of the concentrations on a very fine time scale.

 

Fixi v1 identity card

The fixi v1 is a micro-station manufactured at Atmo Auvergne-Rhône-Alpes. It is based on the open source sensor.community system, developed by the OK Lab in Stuttgart as part of the "Code for Germany" project. Information about this project is available at sensor.community. 

The Fixi is composed of several electronic elements, the most essential of which are:

  • A microcontroller (nodemCU ESP8266) which is the "brain" of the station. It contains the instructions in the form of a code (or firmware) that drives the sensor to perform the measurements and transfer them via Wifi to one (or more) servers. 
  • A particulate measurement sensor (or sensor) that allows to measure fine particles in the ambient air. The particle sensor chosen for this version of Fixi is the PMS7003 of the Plantower brand (identical to the Mobi sensor).
  • A temperature and relative humidity sensor (DHT22).


Characteristics:

Weight: 400 g 

Particle sensor: Plantower PMS7003 

Temperature and relative humidity: DHT22 

Wifi: NodeMCU - esp8266

 

Technical constraints

To be able to operate and transmit its data, a Fixi micro-station must be electrically connected (5V power supply) and connected in Wifi to an internet box. Once the station is correctly configured on a Wifi network, the data from the station automatically passes through the box to the servers of Atmo Auvergne-Rhône-Alpes. It is also possible to transfer them to the official servers of sensor.community.

 

How are the measurements made?

To count the particles, the Fixi uses an optical measurement method based on laser technology. A ventilator allows the outside air to enter and drive it through a detection chamber. This air containing fine particles passes in front of a laser beam that will be intercepted by the particles. A photodetector (diode) measures the difference between the light sent and the light scattered by the particles (decrease in light intensity) and counts their number in size ranges. The electrical signal of the photodiode is then transmitted to a microcontroller which processes the data in real time: knowing the flow rate of the fan and the diameter of the section, a number of particles can be determined, then a concentration can be estimated according to it using a conversion algorithm.