CamjamEduKit Sensors Worksheet 3

[Jgk54]

I'm am very new at this but cannot get the temperature. py
to run. It fails on line 12.
device_folder = glob.glob(base_dir+'28*')[0]
IndexError: list index out of range

This is my first delve into python, I have double checked the line and it seems to be typed correctly. I would be grateful to know if anyone else has managed to run the code correctly. If they have then I will have to investigate further.

[mahjongg]

do you even understand the code?
base_dir+'28*'
seems strange to me if the result should be numerical. especially that asterix I would not expect it there.

[rpdom]

do you even understand the code?
base_dir+'28*'
seems strange to me if the result should be numerical. especially that asterix I would not expect it there.

It looks like it is looking for a ds18b20 if base_dir = "/sys/bus/w1/devices/" then it would pick up the names of the devices that all start with "28-".

To the OP (Jgk54): Have you made sure the driver modules for the w1_gpio and w1_therm have been loaded?
Does the sensor appear in the base_dir? (try "ls /sys/bus/w1/devices/28*" in a terminal and see if it gives any results).

[DirkS]

do you even understand the code?
base_dir+'28*'
seems strange to me if the result should be numerical. especially that asterix I would not expect it there.

That code is from the worksheet: https://www.dropbox.com/s/crtabzm3l5mb4 ... e.pdf?dl=0 (page 4)
You would expect that works...

[DirkS]

do you even understand the code?
base_dir+'28*'
seems strange to me if the result should be numerical. especially that asterix I would not expect it there.

It looks like it is looking for a ds18b20 if base_dir = "/sys/bus/w1/devices/" then it would pick up the names of the devices that all start with "28-".

To the OP (Jgk54): Have you made sure the driver modules for the w1_gpio and w1_therm have been loaded?
Does the sensor appear in the base_dir? (try "ls /sys/bus/w1/devices/28*" in a terminal and see if it gives any results).

+1
Page 3 of the worksheet describes loading the modules and checking for the devices.

[DougieLawson]

I'm am very new at this but cannot get the temperature. py
to run. It fails on line 12.
device_folder = glob.glob(base_dir+'28*')[0]
IndexError: list index out of range

This is my first delve into python, I have double checked the line and it seems to be typed correctly. I would be grateful to know if anyone else has managed to run the code correctly. If they have then I will have to investigate further.

I've just tried this code

Code: Select all

# Import Libraries
import os
import glob
import time

# Initialize the GPIO Pins
os.system('modprobe w1-gpio') # Turns on the GPIO module
os.system('modprobe w1-therm') # Turns on the Temperature module

# Finds the correct device file that holds the temperature data
base_dir = '/sys/bus/w1/devices/'
device_folder = glob.glob(base_dir + '28*')[0]
device_file = device_folder + '/w1_slave'

# A function that reads the sensors data
def read_temp_raw():
  f = open(device_file, 'r') # Opens the temperature device file
  lines = f.readlines() # Returns the text
  f.close()
  return lines

# Convert the value of the sensor into a temperature
def read_temp():
  lines = read_temp_raw() # Read the temperature 'device file'
  
  # While the first line does not contain 'YES', wait for 0.2s
  # and then read the device file again.
  while lines[0].strip()[-3:] != 'YES':
    time.sleep(0.2)
    lines = read_temp_raw()

  # Look for the position of the '=' in the second line of the
  # device file.
  equals_pos = lines[1].find('t=')

  # If the '=' is found, convert the rest of the line after the
  # '=' into degrees Celsius, then degrees Fahrenheit
  if equals_pos != -1:
    temp_string = lines[1][equals_pos+2:]
    temp_c = float(temp_string) / 1000.0
    temp_f = temp_c * 9.0 / 5.0 + 32.0
    return temp_c, temp_f

# Print out the temperature until the program is stopped.
while True:
  print(read_temp())
  time.sleep(1)

on a system that doesn't have the 1-wire interface enabled and doesn't have any 1-wire devices connected and I get exactly the same error as you've seen.

Step back to page3 of the PDF and check everything again.

Open a Terminal Window:

• Enter the following command: sudo modprobe w1-gpio
• Followed by: sudo modprobe w1-therm
• Go to the ‘devices’ directory: cd /sys/bus/w1/devices
• View the devices, and check that you see “28-00000626cc81” (the number following “28-” may vary). If you see the number, then the changes have taken affect and the sensor should now work:
  ls –l

[Jgk54]

Managed to get it all working. Many thanks for your help. I had indentation problems when typing the code. Learnt the hard way.

[DougieLawson]

Managed to get it all working. Many thanks for your help. I had indentation problems when typing the code. Learnt the hard way.

Any code printed in a PDF is a monster pain because cut'n'paste doesn't work. Anything written in python is a monster pain because the stupid language has syntax that relies on space on the left. Add the two together and you're heading for a disaster.