UART Rx TX pins not reading sensor output RPI3

Question

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")
ser.flushInput()
time.sleep(1,21)

for i in range(1):

    ser.flushInput()
    ser.write(b"\xFE\x44\x00\x08\x02\x9F\x25")
    time.sleep(.5)
    resp = ser.read(7)
    high = ord(resp[3])
    low = ord(resp[4])
    co2 = (high*256) + low
    print ("i = ",i, " CO2 = " +str(co2))
    time.sleep(.1)

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.

Answer 1

Start again with a fresh install.

1. Use raspi-config to enable serial.
2. Use /dev/serial0 in your script.