Co2 sensor not working

Archives GrovePi
1

hi,

I´m just trying to get the Co2 MH-Z16 up and running. I´m using a raspberry pi 3 b+ wit a grove pi+. So far i disabeld serial communication, diabeld the blothoth on s0 and the Sensor is connected to the priser port of the grove pi+. When im using the python Co2 test script (https://github.com/DexterInd/GrovePi/tree/master/Software/Python/grove_co2_sensor) i get the following output:

_Traceback (most recent call last):_
_  File "/ directory/sensor.py", line 7, in <module>_
_    [ppm,temp]= co2.read()_
_  File "/directory/grove_co2_lib.py", line 24, in read_
_    ser.write(self.cmd_get_sensor)_
_  File "/directory/serialposix.py", line 518, in write_
_    d = to_bytes(data)_
_  File "/directory/serialutil.py", line 63, in to_bytes_
_    raise TypeError('unicode strings are not supported, please encode to bytes: {!r}'.format(seq))_
_TypeError: unicode strings are not supported, please encode to bytes: 'ÿ\x01\x86\x00\x00\x00\x00\x00y'_

thats the problem so far…

2

hi again,

i came a little bit fürther… by changing the codeline in the python libary at line 13 to:
cmd_get_sensor = b"\xff\x01\x86\x00\x00\x00\x00\x00\x79"
the bytes seem to be send but i get the following error message:

Traceback (most recent call last):
  File "/home/pi/netzspeicher/Generic-FlashDisk-01/sensor.py", line 7, in <module>
    [ppm,temp]= co2.read()
  File "/home/pi/netzspeicher/Generic-FlashDisk-01/grove_co2_lib.py", line 26, in read
    high_level = struct.unpack('B', self.inp[2])[0]
TypeError: a bytes-like object is required, not 'int'

so it sends data back but not in bytes but in integers, so may anyone can help me with that so i can recive bytes instead of integers?
any help is welcomed

3

Hi @hugo112,

I think it may be using Python 3. Can you tell us which version are you using? If it’s Python 3, can you give it a shot with Python 2 instead?

Thank you!

4

hi,

thanks for ur reply, but i got it working in the meantime.

5

Hi @hugo112,

That’s great. What was that did it for you?

Thanks!

6

hi,

i just worked through the errors i got till it worked… im new to programing so im a little astonished myself. I can post the code if u like me to.

7

Hi @hugo112,

Yeah sure, why not. Thanks a lot! :slight_smile:

8

hi,

sure no problem, here is th new grove_co2_lib:

import serial
# import time

ser = serial.Serial(’/dev/ttyAMA0’, 9600, timeout = 1)

class CO2:

inp = []
cmd_calibrate_sensor = b"\xff\x87\x87\x00\x00\x00\x00\x00\xf2"
cmd_get_sensor = b"\xff\x01\x86\x00\x00\x00\x00\x00\x79"

def init(self):
ser.flush()

def calibration(self):
ser.write(self.cmd_calibrate_sensor)
cal = “calibration Done”
return[cal]

def read(self):
try:
ser.write(self.cmd_get_sensor)
self.inp = ser.read(9)
high_level = self.inp[2]
low_level = self.inp[3]
temp_co2 = self.inp[4] - 46
conc = high_level * 256 + low_level
return [conc, temp_co2]

except IOError:
return [-1, -1]

# if name == “main”:
# while True:
# print(CO2.read())
# time.sleep(1)

9

oh, i didnt post the tabs, sorry

10

Hi…
i used the code and run with python3 & python2 output shows blank screen. any modification in the code?

import serial
import time

ser = serial.Serial('/dev/ttyAMA0', 115200, timeout = 1)

class CO2:

        inp = []
        cmd_calibrate_sensor = b"\xff\x87\x87\x00\x00\x00\x00\x00\xf2"
        cmd_get_sensor = b"\xff\x01\x86\x00\x00\x00\x00\x00\x79"

        def init(self):
                ser.flush()

        def calibration(self):
                ser.write(self.cmd_calibrate_sensor)
                cal = "calibration Done."
                return[cal]

        def read(self):
                try:
                        print("1")
                        ser.write(self.cmd_get_sensor)
                        print("2")
                        self.inp = ser.read(9)
                        print("3")
                        high_level = self.inp[2]
                        print("4")
                        low_level = self.inp[3]
                        print("5")
                        temp_co2 = self.inp[4] - 46
                        print("6")
                        conc = high_level * 256 + low_level
                        print("7")
                        return [conc, temp_co2]

                except IOError:
                        return [-1, -1]

if "main" == "main":
        C = CO2()
        while True:
                print(C.read())
                time.sleep(1)
11

Hi @nagaraju.grandhi7,

There can be a couple of reasons:

  1. You didn’t connect the sensor to the right port. That being the RPISER port of the GrovePi.

  2. You didn’t switch the hardware serial port (/dev/ttyAMA0) to point to the appropriate hardware pins instead of not letting it be used by the Bluetooth - especially important on Pi3/Pi3 B+.

  3. Something is wrong with the code.

As for making sure you’ve got the serial port configured properly, check this page. Everything is described in detail:

Thank you!