OSHW High precision calibrated digital air quality CO2, temperature, humidity, air pressure sensor board with UEXT connector


Analog gas and air quality sensors have quite negligent readings. They need special calibration to measure correctly.

This is why CCS811B digital air quality sensor by AMS is so interesting. It can measure indoor air quality and CO2 content with digital readings from 400 up to 29206 ppm.

MOD-ENV has CCS811B and BME280 digital precise temperature, humidity and air pressure sensor assembled together. Both operate through I2C and are low power with sleep modes which makes them perfect for enviroment monitoring and IoT.

ESP32-POE, ESP32-POE-ISO, ESP32-EVB has UEXT connectors and can directly connect to MOD-ENV.

The price of MOD-ENV is between EUR 14.36 and 15.95 depend on quantity.

MOD-BME280 precise Humidity, Temperature and Pressure sensor Open Source Hardware module with UEXT and Breadboard connector


BME280 is digital humidity, temperature and pressure sensor with I2C and SPI interface.

You can see on this link comparison of different Humidity sensors

The operating conditions are:

  • Temperature -40..+85C;
  • Humidity 0…100 % Rh;
  • Pressure 300…1100 hPa  (+9000m..-500m above sea level);

The sensor works on 3.3V and is with very low power consumption 0,1..3,6 uA.

The easiest way to connect MOD-BME280 is with UEXT connector to any board with UEXT connector as shown on the picture above.

For boards which has no UEXT connector MOD-BME280 can be connected via four jumper wires on breadboard:


The KiCad files are uploaded on GitHub.

The demo software use Adafruit BME280 libraries with two small modifications. The default address in MOD-BME280 is 0x76 while Adafruit library is set to 0x77.

UEXT connector requires D8 to be set LOW to power and 10 ms delay to settle the power before addressing the sensor. The code is at GitHub.

When you run it you will see this:

Screenshot from 2018-03-27 14-35-38

The sensor is very precise, if you move board up and down you can see altitude changes. The 171 meter is the altitude of Olimex building.

MOD-BME280 is perfect for IoT application for environmental conditions logging due to the low power consumption and precise measurements. It can be used both for indoor and outdoor applications.

DuinoMite Project: Low cost Humidity measurement with SMTHS07 capacitive sensor


SMTHS07 is low cost EUR 5.00 capacitive Humidity sensor from Smartec. The datasheet of this sensor is here.

The sensor change it’s capacitance linear in range 20-95% with 0.6 pf/RH.

Now the question is will DuinoMite be able to detect so small capacitive changes of 0.6 pf?

Let’s do some experimenting first. I made small schematic on breadboard-mini with two resistors and the sensor:


then wrote small BASIC code:

10 PIN(1)=0 ‘sense pin will first pull the capacitor to GND and discharge
20 A=0 ‘accumulator
30 FOR I = 1 TO 1000 ‘measure 1000 times and average to remove noise
40 SETPIN 1,8 ‘discharge the capacitor
50 SETPIN 1,1 ‘start charging
60 A = A + PIN(1) ‘accumulate the readings
80 A = A / 1000 ‘now divide by 1000 to normalize the result
90 PRINT A ‘let’s see the result
100 GOTO 20

the result was steady:

> run

if I approach the sensor with wet fingers the reading go to

So the sensitivity is quite good! All I need is calibration of the sensor, but how to do this?

How to Preciese calibrate SMTHS07 is explained here .
Poor’s man calibration is to put the sensor it in refrigerator, the humidity in refrigerator is always 100%. As SMTHS07 is linear knowing the capacitance in just one point is enough to calibrate it.