This is the first post about our RESPIRA sensor, a low-cost multi-environmental sensor device for urban spaces. This wireless node measures CO and NO2 levels, temperature and humidity and takes its power from any source capable to supply between 6 and 12 VDC.
Figure 1 : RESPIRA sensor
Temperature and humidity readings are taken from a DHT22 sensor whilst CO and NO2 are provided by a MiCS-4514 IC made by e2v Technologies and distributed by SGX Sensortech. This is not properly a low-power device since the MiCS-4514 sensor needs to be always on. Besides, like other sensors capable to measure concentration of suspended particles in the air, it needs a heater (one per sensor) to be continuously draining current from our power source.
The MiCS-4514 chip is very popular among the green urban community. AirQualityEgg uses in fact one of these IC's and our friends from the IOT Madrid group have been evaluating this dual sensor as well. We seem to have little choice at this moment but we will be soon evaluating other sensors with different power requirements.
Precision of these sensors is also an issue. Most of them are made for the car industry so we may say that they have not been initially designed and precalibrated to measure low concentrations of particles. In order to gain precision at the lower concentration ranges, these sensors would need to be recalibrated. In any case, readings transmitted by our RESPIRA sensor must be considered only as an approximate indicator of the air quality.
The following is a list of concentration ranges of CO and NO2 according to different studies. This is a summary in fact, used for our own evaluation. The code of colors is quite self-explanatory:
For NO2: ppb (parts per billion), hourly rate:
For CO: ppm (parts per million), hourly rate:
Like any other panStamp device, our RESPIRA sensor can be "connected" to different cloud data services as Cosm, ThingSpeak, sen.se or Twitter by means of Lagarto, our open automation software.
This sensor, along with other sensor and control boards, will be showcased in our stand at CeBIT 2013 - from 05 to 09 March in Hannover, Germany - as part of the finalists of the CODE_n contest which turns around a common argument: urban sustainability.
Sample sketches, including the one for the RESPIRA sensor.