Use Raspberry Pi as air measurement device

This repository includes files for:

• Measure air condition using some sensors connected to Raspberry Pi
  • CO2 Concentration using MH-Z19B
  • Temperature using BME280 or DS18B20
  • Humidity using BME280
  • Air Pressure using BME280
• Publish these values to MQTT broker

Use MH-Z19B

MH-Z19B can measure CO2 concentration.

Layout

Sensor Side	Raspberry Pi Side
GND	GND
Vin	5 V
TXD	RXD (8)
RXD	TXD (10)

Raspberry Pi configuration

MH-Z19B use UART. You have to enable Serial port and disable Shell over Serial.

$ sudo raspi-config nonint do_serial 2

Use BME280

BME280 can measure temperature, humidity, and air pressure.

Layout

Sensor Side	Raspberry Pi Side
GND	GND
VCC	3.3 V
SCL	GPIO3 (5)
SDA	GPIO2 (3)

Raspberry Pi configuration

BME280 use I2C. You have to enable this feature.

$ sudo raspi-config nonint do_i2c 0

You can check connectivity by i2cdetect command. If you can see 0c76 as follows, it's connected correctly.

$ sudo i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- 76 --            

Use DS18B20

DS18B20 can measure temperature.

Layout

Sensor Side	Raspberry Pi Side
GND	GND
Vin	3.3 V
Signal	GPIO4 (7)

Raspberry Pi configuration

DS18B20 use interface called "One-Wire". You have to enable this feature.

$ sudo raspi-config nonint do_onewire 0
$ sudo reboot

The first One-Wire bus has to be connected GPIO4 (7).

If you want to use a pin other than GPIO4, append strings ,gpiopin=4 to the end of of dtoverlay=w1-gpio and reboot.

$ sudo vi /boot/config.txt
$ grep dtoverlay=w1-gpio /boot/config.txt
dtoverlay=w1-gpio,gpiopin=4
$ sudo reboot

And then load some modules.

$ sudo modprobe w1-gpio
$ sudo modprobe w1-therm

Then you can see the directory start with 28- in /sys/bus/w1/devices directory.

The file w1_slave in this directory includes current temperature.

pi@raspberrypi:~ $ cat /sys/bus/w1/devices/28-01186d8e8fff/w1_slave 
7a 01 4b 46 7f ff 0c 10 ec : crc=ec YES
7a 01 4b 46 7f ff 0c 10 ec t=23625

In this example, the value t=23625 means 23.625 degrees Celsius.