Previous post: In-the-Air-Challenge: Exploring internally NDIR CO2 monitor
EXTECH CO100 air quality monitor has a very compact CO2 sensor module made by SenseAir that puts out a PWM type signal proportional to concentration. To interface the EXTECH NDIR CO2 monitor with IoT I could very well use the Texas Instruments CC3200 Wi-Fi connectivity board donated by Element 14 for In-the-Air-Challenge. +5V power to the CC3200 board comes from the EXTECH circuit. I had to use a linear regression to fit LCD data with CC3200 data:
ppm = ms * 10 * 1.0013 + 86
CC3200 uploading values to Xively is described in my previous Backyard Challenge roadtest posts:
You can visit the Xively feed here:
CC3200 demo board works well but is quite large and can not fit inside the monitor enclosure. (ArduinoPro mini+ ESP8266 fits inside the EXTECH enclosure.)
Internet of Things simplifies life a lot. If there was no IoT then it would be much more effort and expensive to make a graph. Would need microcontroller, SD card, RTC, manually transfer file to a PC, plot it. So far I feel to be done with the CO2 monitoring electronics and next week will turn to photodiode circuit counting airborne dust particles.
After a weekend there is some data to analyse:
Sensor is inside the office in the downtown Riga. It shows that during working day air in the office is OK. In the city CO2 content decreases in the night and starts to rise at 6:20 in the morning. After 19 pm the air becomes cleaner all over the night until at 6:20 morning traffic begins. Sensor is inside building so it takes extra hours until air ventilates.
On a short time scale there is some strange periodic spiking appearing roughly every 10 minutes. This could be some internal PID regulation inside the Sensair sensor. There is a typical shape of the spike going upwards and then downwards. So the average value is not so much influenced. Spiking peak-to-peak amplitude is about 75 ppm that is consistent with the EXTECH datasheet specified precision of 75 ppm.
Here is format how to get out picture from Xively for a defined period of time with manual vertical scale values: