This is my first pi project so I'm a bit new at this. I'm trying to connect a senseair K-30 CO2 sensor to the pi via the UART gpio pins. This is the sensor I am using: https://www.co2meter.com/products/k-30-co2-sensor-module

and I set it up following the app note here: http://www.co2meters.com/Documentation/AppNotes/AN137-K30-sensor-raspberry-pi-uart.pdf

I have done some changes to try to get it to work in python3

However, the co2 comes up with a error message. If I use /dev/ttyS0 I get the error message. Traceback (most recent call last): File "K-30_3.py", line 18, in high = ord(resp[3]) IndexError: index out of range. But if I use /dev/ttyAMA0 it seems to do nothing.

What I've done so far:

  • Went into raspi-config and under interfacing options, changed "Would you like a login shell to be accessible over serial?" to "No" and "Would you like the serial port hardware to be enabled" to "Yes"
  • Added the line enable_uart=1 and dtoverlay=pi3-disable-bt to the /boot/config.txt file.
  • Deleted the line console=/dev/ttyS0,115200 in the /boot/cmdline.txt file.
  • Did both systemctl stop [email protected] and systemctl disable [email protected].

I'm still a little confused and any help would be much appreciated!

Here is what the sensor uses:

#rpi serial connections
#Python app to run a K-30 Sensor
import serial
import time

ser = serial.Serial("/dev/ttyS0",baudrate =9600,timeout = .5)
print ("  AN-137: Raspberryu Pi3 to K-30 Via UART\n")

for i in range(1):

    resp = ser.read(7)
    high = ord(resp[3])
    low = ord(resp[4])
    co2 = (high*256) + low
    print ("i = ",i, " CO2 = " +str(co2))

And the output:

  AN- 137: Raspberry Pi3 to K-30 via UART

Traceback (most recent call last):
  File "K-30_3.py", line 18, in <module>
    high = ord(resp[3])
IndexError: index out of range

However, if I change ser = serial.Serial("/dev/ttyS0",baudrate =9600,timeout = .5) to ser = serial.Serial("/dev/ttyAMA0",baudrate =9600,timeout = .5)

The output is this:

  AN- 137: Raspberry Pi3 to K-30 via UART

It is either doing nothing or is hanging.

I'm using Python 3.7 on Raspberry Pi OS Codename Buster.

  • It is difficult to understand WHY you would have done this or what OS you are using. Try a fresh install and don't fiddle with boot files.
    – Milliways
    Oct 22, 2021 at 10:31
  • I'm using 'Python 3.7' on Raspberry Pi OS Codename 'Buster'.
    – Marc
    Oct 25, 2021 at 11:03

1 Answer 1


Start again with a fresh install.

  1. Use raspi-config to enable serial.
  2. Use /dev/serial0 in your script.
  • I have done a fresh install and what you have suggested. However I still get the same results. Thanks for the suggestion
    – Marc
    Oct 25, 2021 at 7:49
  • Please edit your post and show the software listing you are using.
    – joan
    Oct 25, 2021 at 7:50
  • 1
    @Marc All relevant information should be edited into your question.
    – joan
    Oct 25, 2021 at 8:46

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