[PYTHON] Make a simple CO2 incubator using Raspberry PI and CO2 sensor (MH-Z14A)

Purpose

Since the microorganisms under study may be alive using trace components in the atmosphere, we will create a culture device that can add them.

Enable UART on the Raspberry Pi side

-UART communication with Raspberrypi 3 (console & general purpose) ・ Measure carbon dioxide concentration with Raspberry Pi 3 Model B + (MH-Z14A) -AWS IoT is also available- Was referred to.

sudo raspi-config ->"5 Interfacing Option" ->"P6 Serial"

You will be asked if you want to log in to the shell serially, so select "No". "Would you like a login shell to be accessible over serial?" -> "No"

You will be asked if you want to enable the serial port, so select "Yes". "Would you like the serial port hardware to be enabled?" -> "Yes"

Select Finish to restart.

continue

$ whoami
pi
$ ls -la /dev/ttyS0
crw-rw---- 1 root dialout 4,64 November 29 10:42 /dev/ttyS0
$ sudo gpasswd -a pi dialout

Module created to use MHZ-14A

Measure carbon dioxide concentration with Raspberry Pi 3 Model B + (MH-Z14A) -AWS IoT is also available- Was referred to.

・ MH-Z14A NDIR CO2 SENSOR FOR CARBON DIOXIDE DETECTION Since the data sheet was updated, I referred to the latest one. The following five commands are set for this sensor.

1. Measurement of CO2 concentration
2. Zero point calibration
3. Span calibration
4. On / off of automatic calibration function
5. Change the measurement range This function is not used this time because a standard gas (or the atmosphere is used as a CO2 concentration of 400 ppm) is required for calibration. I put in commands to measure CO2 concentration, turn off automatic calibration, and change the measurement range. Automatic calibration is a function that automatically performs zero point calibration once every 24 hours, and it is recommended not to use this function when using it in greenhouses, farms, and refrigerators.

When reading the referenced code ・ Definition of class and meaning of init and self ・ How to use pyserial -Making a module and meaning ʻif name =='main': ` I didn't know much about such things, so I made something that works for the time being, but I'm not confident in the accuracy of the code.

I saved the created mhz14a.py in /usr/lib/python2.7/dist-packages/. Reference; 3rd edition p195

mhz14a.py

import serial
import time

class MHZ14A():
    PACKET = [0xFF, 0x01, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00, 0x79]
    RANGE1 = [0xFF, 0x01, 0x99, 0x00, 0x00, 0x00, 0x07, 0xd0, 0x8F]
    RANGE2 = [0xFF, 0x01, 0x99, 0x00, 0x00, 0x00, 0x13, 0x88, 0xCB]
    RANGE3 = [0xFF, 0x01, 0x99, 0x00, 0x00, 0x00, 0x27, 0x10, 0x2F]
    AUTOCALON = [0xFF, 0x01, 0x79, 0xA0, 0x00, 0x00, 0x00, 0x00, 0xE6]
    AUTOCALOFF = [0xFF, 0x01, 0x79, 0x00, 0x00, 0x00, 0x00, 0x00, 0x86]

    def __init__(self, ser):
        self.serial = serial.Serial(ser, 9600, timeout=1)
        time.sleep(2)

    def get(self):
        self.serial.write(bytearray(MHZ14A.PACKET))
        res = self.serial.read(size=9)
        res = bytearray(res)
        checksum = 0xff & (~(res[1] + res[2] + res[3] + res[4] + res[5] + res[6] + res[7]) + 1)
        if res[8] == checksum:
            return (res[2] << 8|res[3])
        else:
            raise Exception("checksum: " + hex(checksum))

    def close(self):
        self.serial.close()

#Acquires and returns the CO2 concentration from the sensor
def main():
    sensor = MHZ14A("/dev/ttyS0")
    try:
        return (int(sensor.get()))
    except:
        pass
    sensor.close()

#Self-On / off of calibration function(No return value)
def autocal(x):
    sensor = MHZ14A("/dev/ttyS0")
    if x == 0:
        sensor.serial.write(bytearray(MHZ14A.AUTOCALOFF))
    elif x == 1:
        sensor.serial.write(bytearray(MHZ14A.AUTOCALON))
    sensor.close()

#Send a command to change the measurement range(No return value)
def range(y):
    sensor = MHZ14A("/dev/ttyS0")
    if y == 1:
        sensor.serial.write(bytearray(MHZ14A.RANGE1))
    elif y == 2:
        sensor.serial.write(bytearray(MHZ14A.RANGE2))
    elif y == 3:
        sensor.serial.write(bytearray(MHZ14A.RANGE3))
    sensor.close

if __name__ == '__main__':
    main()

・ Main () returns the sensor value ・ Autocal (x) is the automatic calibration function on (1) off (0) ・ Range (y) has 3 ways of changing the measurement range, 0 ~ 2000, 0 ~ 5000, 0 ~ 10000, and the initial setting of the machine is 5000.

Acquires CO2 and turns the solenoid valve on and off

I wrote it with reference to the code of L Chika. The automatic calibration function is turned off and the measurement range is set to 0 to 10000ppm.

import RPi.GPIO as GPIO
from time import sleep
import datetime
import mhz14a as MHZ

GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.OUT)

MHZ.autocal(0) #self-Turn off calibration function
MHZ.range(3) #Measurement range is 0~Set to 10000ppm

try:
    while True:
        ppm = MHZ.main() #Get the value of the sensor
        if ppm < 9500: #CO2 concentration that opens the solenoid valve
            GPIO.output(18, True)
            sleep(0.2) #Time to open solenoid valve(Seconds)
            GPIO.output(18, False)
            sleep(0.8)
        else:
            sleep(1)
        print(ppm, datetime.datetime.now()) #Display CO2 concentration and date / time
        sleep(60) #Measurement interval(Seconds)
except KeyboardInterrupt:
    pass

GPIO.cleanup()
print("stop")

Solenoid valve on / off

・ Solenoid valve JPMV22NC (bought at Amazon) ・ 12V power supply attached to solenoid valve ・ DC-DC converter SUS1R50505 ・ OMRON G5V-2 (If it is not this size, it will not stick to the breadboard) ・ Transistor S8050 (I bought it in a pack with an assortment of Amazon) ・ 1000Ω resistor (bought with Amazon assortment pack) ・ Diode (bought in Amazon's assortment pack) When I tried to draw a circuit diagram, Firitzing was charged, so I took a direct shot on the breadboard. At first, the solenoid valve didn't work and I couldn't understand everything, so I connected the 5V GND to the Raspberry Pi's GND and it worked. It's difficult ...

I tried to move it for the time being

As shown in the photo, the sensor, CO2 outlet and fan are packed in a tapper, lightly covered (not completely sealed), and moved overnight. The result is the graph below.

Since the upper limit of the sensor is 10000ppm, I'm shaking it off, but I think I can maintain around 10000ppm. Speaking of greed, I want a measurement range up to about 10%, but there is nothing affordable.

Future tasks

・ Save log -Added hydrogen, methane, and carbon monoxide sensors (I bought the sensor itself, but AD conversion is required) → Trace gas incubator