mh-z19b-driver is a java library that operates CO2 gas concentration sensor called MH-Z19B to connect MH-Z19B to GPIO terminal of Raspberry Pi 3B and make it for use in java. I releases this in the form of the Eclipse plug-in project. You need Java 8 or higher.

I use jSerialComm for serial communication in java and have confirmed that it works in Raspberry Pi 3B (Raspbian Buster Lite OS (2019-07-10)).

Connect with Vin <--> Vin,GND <--> GND, but connect Tx and Rx mutually to enable transmission / reception. Tx <--> Rx, Rx <--> Tx

• 6. Pins of MH-Z19B
  • Vin
  • GND
  • Tx
  • Rx
• GPIO of Raspberry Pi 3B
  • Vin --> (2) or (4)
  • GND --> (6), (9), (14), (20), (25), (30), (34) or (39)
  • Tx --> (8) GPIO14
  • Rx --> (10) GPIO15

In addition, I was able to use MH-Z19B using DSD TECH SH-U09C USB to TTL Serial Adapter with FTDI FT232RL Chip instead of GPIO of Raspberry Pi 3B. At that time, I set /dev/ttyUSB0 as the serial port name.

The reason for using this version is that it is the latest as of July 2019 and BlueZ 5.50 is included from the beginning, and use Bluetooth and serial communication simultaneously.

• Edit /boot/cmdline.txt

console=serial0,115200 --> removed

• Edit /boot/config.txt

@@ -45,7 +45,7 @@
 # Uncomment some or all of these to enable the optional hardware interfaces
 #dtparam=i2c_arm=on
 #dtparam=i2s=on
-#dtparam=spi=on
+dtparam=spi=on
 
 # Uncomment this to enable the lirc-rpi module
 #dtoverlay=lirc-rpi
@@ -55,6 +55,10 @@
 # Enable audio (loads snd_bcm2835)
 dtparam=audio=on
 
+enable_uart=1
+dtoverlay=pi3-miniuart-bt
+core_freq=250
+
 [pi4]
 # Enable DRM VC4 V3D driver on top of the dispmanx display stack
 dtoverlay=vc4-fkms-v3d

When editing is complete, reboot. Now you can use /dev/ttyAMA0 for serial communication without conflicting with Bluetooth.

For example, the installation of OpenJDK 8 is shown below.

# apt-get update
# apt-get install openjdk-8-jdk

If git is not included, please install it.

# apt-get install git

• SLF4J 1.7.26
• jSerialComm 2.5.1

I would like to thank the authors of these very useful codes, and all the contributors.

The following sample code will be helpful. Reading sensor data immediately after open may give a strange value, but I think that the normal values will be obtained after the second time.

import io.github.s5uishida.iot.device.mhz19b.driver.MHZ19BDriver;

public class MyMHZ19B {
    private static final Logger LOG = LoggerFactory.getLogger(MyMHZ19B.class);
    
    public static void main(String[] args) throws IOException {
        MHZ19BDriver mhz19b = null;
        try {
            mhz19b = MHZ19BDriver.getInstance("/dev/ttyAMA0");
            mhz19b.open();
            mhz19b.setDetectionRange5000();
            mhz19b.setAutoCalibration(false);
            
            while (true) {
                int value = mhz19b.getGasConcentration();
                LOG.info("co2:" + value);
                
                Thread.sleep(10000);
            }
        } catch (InterruptedException e) {
            LOG.warn("caught - {}", e.toString());
        } catch (IOException e) {
            LOG.warn("caught - {}", e.toString());
        } finally {
            if (mhz19b != null) {
                mhz19b.close();
            }
        }
    }
}