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Cannot Connect to MH_Z19B Sensor - code fix attached #1315

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tledwar opened this issue Jun 16, 2023 · 5 comments
Open

Cannot Connect to MH_Z19B Sensor - code fix attached #1315

tledwar opened this issue Jun 16, 2023 · 5 comments

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@tledwar
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tledwar commented Jun 16, 2023

This is related to https://forum.radicaldiy.com/t/mh-z19b-not-work-with-mycodo-python-but-works-with/1563 which was posted on the forum.

Mycodo Version: 8.15.9
OS: Linux raspberrypi 6.1.21+ #1642 armv6l GNU/Linux
Platform: Pi Zero W

Issue:

Unable to get data from the sensor.

Reproduce Issue:

These items are mentioned in the above forum post and was part of the troubleshooting. I have not tried to not do these changes after I found a code fix.
Reviewed https://forum.radicaldiy.com/t/mh-z19b-wiring-sanity-check/677 to properly wire up the sensor
Disable Bluetooth and uninstal Py libraries
/boot/config.txt:

Disable Bluetooth

dtoverlay=disable-bt
[all]
enable_uart=1

Create an Input for MH_Z19B
image

Testing was done with the following configured serial ports:

  • ttyAMA0
  • ttyS0
  • serial0

Although it is worth noting the following linked serial ports at the OS level:
ls -la /dev/ser*
lrwxrwxrwx 1 root tty 7 Jun 9 10:22 /dev/serial0 → ttyAMA0
lrwxrwxrwx 1 root root 5 Jun 9 10:22 /dev/serial1 → ttyS0

After testing, the proper port to use at least on this platform is /dev/serial0.
image

Once the proper port is configured and the system runs, the following error is generated:

2023-06-16 12:05:05,067 - ERROR - mycodo.inputs.mh_z19b_6a3d18a1 - UART Location: "/dev/serial0".
2023-06-16 12:05:05,177 - DEBUG - mycodo.controllers.controller_input_6a3d18a1 - get_measurement() found
2023-06-16 12:05:05,179 - DEBUG - mycodo - Input controller with ID 6a3d18a1-c77a-421b-8a71-8be78a91bf88 activated.
2023-06-16 12:05:05,185 - DEBUG - mycodo.controllers.controller_input_6a3d18a1 - listener() not found
2023-06-16 12:05:05,209 - INFO - mycodo.controllers.controller_input_6a3d18a1 - Activated in 5605.7 ms
2023-06-16 12:05:06,238 - DEBUG - mycodo.inputs.mh_z19b_6a3d18a1 - No response
2023-06-16 12:05:06,425 - DEBUG - mycodo.controllers.controller_input_6a3d18a1 - Adding measurements to InfluxDB with ID 6a3d18a1-c77a-421b-8a71-8be78a91bf88: {}
2023-06-16 12:05:07,993 - INFO - mycodo.controllers.controller_input_69d8bf11 - Activated in 1929.7 ms
2023-06-16 12:05:07,994 - DEBUG - mycodo - Input controller with ID 69d8bf11-ef3d-405e-b7be-5696fae74a07 activated.

No response error is coming from this section of the code from inputs/mh_z19b.py:

try:
            self.ser.flushInput()
            self.ser.write(bytearray([0xff, 0x01, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00, 0x79]))
            time.sleep(.01)
            resp = self.ser.read(9)

            if not resp:
                self.logger.debug("No response")
            elif len(resp) < 4:
                self.logger.debug("Too few values in response '{}'".format(resp))
            elif resp[0] != 0xff or resp[1] != 0x86:
                self.logger.error("Bad checksum")
            elif len(resp) >= 4:
                high = resp[2]
                low = resp[3]
                co2 = (high * 256) + low
                self.value_set(0, co2)
        except:
            self.logger.exception("get_measurement()")
        finally:
            self.measuring = False

Expected behavior

The system shall be able to read values from the sensor.

Potential Code Fix

After some comparison to https://github.com/UedaTakeyuki/mh-z19 (please note this library is mentioned several times in the Mycodo mh_z19b code), I discovered one key difference and it was the stop and start of a getter service. Whenever a connection was made to the serial port for this sensor, the third party library had a control feature to start/stop the service. The service was related to below:

$ systemctl --type=service --state=running | grep getty
getty@tty1.service loaded active running Getty on tty1
serial-getty@serial0.service loaded active running Serial Getty on serial0
serial-getty@ttyAMA0.service loaded active running Serial Getty on ttyAMA0

I added these two methods to mh_z19b.py:

def start_getty():
  start_getty = ['sudo', 'systemctl', 'start', 'serial-getty@serial0.service']
  p = subprocess.call(start_getty)

def stop_getty():
  stop_getty = ['sudo', 'systemctl', 'stop', 'serial-getty@serial0.service']
  p = subprocess.call(stop_getty)

Then I added a call to these methods before and after the connection to the serial port in def initialize(self).

    def initialize(self):
        import serial

        self.logger.error('UART Location: "{dev}".'.format(
            dev=self.input_dev.uart_location))

        stop_getty()

        if is_device(self.input_dev.uart_location):
            try:
                self.ser = serial.Serial(
                    port=self.input_dev.uart_location,
                    baudrate=self.input_dev.baud_rate,
                    timeout=1,
                    writeTimeout=5)
            except serial.SerialException:
                self.logger.exception('Opening serial')
        else:
            self.logger.error('Could not open "{dev}". Check the device location is correct.'.format(
                dev=self.input_dev.uart_location))

        if self.abc_enable:
            self.abcon()
        else:
            self.abcoff()

        if self.measure_range:
            self.set_measure_range(self.measure_range)

        start_getty();

        time.sleep(0.1)

For the get_measurement(self) method, I had to do a little more work.
First it was necessary to add a new connection to the device. This method was reusing the old connection and it did not seem to work.
Second, I added a retry around the write command. This was used in the third party code.
And finally, the stop/start Getty commands.

    def get_measurement(self):
        """Gets the MH-Z19's CO2 concentration in ppmv."""
        import serial

        if not self.ser:
            self.logger.error("Error 101: Device not set up. See https://kizniche.github.io/Mycodo/Error-Codes#error-101 for more info.")
            return

        self.return_dict = copy.deepcopy(measurements_dict)

        while self.calibrating:
            time.sleep(0.1)
        self.measuring = True

        stop_getty()

        if is_device(self.input_dev.uart_location):
            try:
                self.ser = serial.Serial(
                    port=self.input_dev.uart_location,
                    baudrate=self.input_dev.baud_rate,
                    timeout=1,
                    writeTimeout=5)
            except serial.SerialException:
                self.logger.exception('Error opening serial port')
        else:
            self.logger.error('Could not open "{dev}". Check the device location is correct.'.format(
                dev=self.input_dev.uart_location))

        try:
            self.logger.debug(self.ser.name)

            for retry in range(5):
                result = self.ser.write(bytearray([0xff, 0x01, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00, 0x79]))
                resp = self.ser.read(9)

            self.logger.debug(len(resp))

            if not resp:
                self.logger.debug("No response")
            elif len(resp) < 4:
                self.logger.debug("Too few values in response '{}'".format(resp))
            elif resp[0] != 0xff or resp[1] != 0x86:
                self.logger.error("Bad checksum")
            elif len(resp) >= 4:
                high = resp[2]
                low = resp[3]
                co2 = (high * 256) + low
                self.value_set(0, co2)
        except:
            self.logger.exception(" Error getting data in get_measurement()")
        finally:
            self.measuring = False

        start_getty()

        return self.return_dict

Based on these code changes, I am actively receiving CO2 values using the input/output/functions defined at https://kylegabriel.com/projects/2021/09/mushroom-cultivation-automation.html

Complete file used during testing:
mh_z19b.py.txt
@kizniche
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This issue has been mentioned on Radical DIY Forum. There might be relevant details there:

https://forum.radicaldiy.com/t/mh-z19b-not-work-with-mycodo-python-but-works-with/1563/3

@kizniche
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I don't think getty is necessary. How are you wiring your sensor?

@tledwar
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tledwar commented Jun 18, 2023 via email

@tledwar
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tledwar commented Jun 18, 2023 via email

@tledwar
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tledwar commented Jun 19, 2023

Connection is like this:

765d35a77294e0bfb98bd98d5a618c4f29b6e377

Sensor is correctly read with https://github.com/UedaTakeyuki/mh-z19 so it should be wired up correctly.

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@kizniche @tledwar