CCS811 VOC & CO2 Gas Sensor

Until just recently I was using analogue gas sensors, ( see previous post 16 January ). I have now turned my attention to digital gas sensors, from which the measurement data are already in digital form.

I am experimenting with the CCS811 sensor which has a I2C digital interface, ( 2-wire bus, clock and data only ). The CCS811 measures the concentration of CO2 ( carbon dioxide ) and TVOC ( total volatile organic compounds, which become a gas at room temperature ) in the air in ppm and ppb respectively which would be useful in giving an indication of air-quality in a closed workshop environment.

I connected an ESP32 micro-controller development board to the CCS811 circuit board and also to a I2C 128x64px blue OLED display in the corner of an already densely populated solderless breadboard.

( top-left) Mauve coloured CCS811 circuit board

The measurement results being displayed were obtained in my basement workshop. There is an established air-quality index called the 'TVOC Index' which is derived from the TVOC ppb concentration. Ppb between 0 & 220 corresponds to a TVOC Index of between 0 & 50 and an 'Index Category' of 'Good' air quality. I am pleased as I spend a lot of time in the basement.

 

I2C = Inter Integrated Circuit

ppm/ppb = parts per million/billion

  

Multi Gas Detector

The 'MQ-' series of gas sensors comprises many different types, and each one is sensitive to one or more specific gases. They are analogue sensors meaning that a voltage is produced that varies with gas concentration. They are also cheap. I bought several MQ-135 and MQ-4 types for use in simple multi gas detectors.

The varying output voltage from the sensor was connected to a 12bit analogue to digital converter on an ESP32 micro-controller development board and the various gas concentrations in the air in the workshop were displayed in parts per million ( ppm ) on a 320x240px colour display.

The MQ-135 sensor is sensitive to the following gases: carbon dioxide, alcohol, carbon monoxide, toluene, ammonia & acetone.

The MQ-135 sensor is near the bottom-left corner

The MQ-4 sensor was used in another multi-gas detector to detect LPG, methane, carbon monoxide, alcohol & smoke.

LPG = Liquefied Petroleum Gas

 

Touch Screen Displays

Nowadays it seems almost obligatory that electronic gadgets have a touch screen display user-interface.

The particular display type I have been trying out recently is a 2.8" 240x320 pixel TFT LCD touch panel display with SPI and using the ILI9341 driver chip. On the back is an SD card slot. Cost when purchased was just under GBP11.

The display and an ESP32 micro-controller development board, ( with my code uploaded to it ), were mounted on a prototyping board and connected up. The ESP32 micro-controller has two built-in sensors; a temperature sensor which measures the CPU temperature, and a Hall-Effect sensor which responds to magnetic fields. Either cpu temperature or magnetic field data can be displayed separately in real-time by tapping on a displayed 'button', which is then highlighted in green.

The CPU temperature measurement has been selected

Although both measurement values could easily have been displayed together, I now have my ready made code to import into future projects which really would benefit from a touch screen.

( SPI = Serial Peripheral Interface, 4-wire bus )