Raspberry Pi Snippets & Code Info

Various code examples & notes for the raspberry pi

UPDATE: [2024-11-18 Mon] These all were relevant when the RPi first arrived, given all the changes, updates etc some may no longer work but I leave them here as a reference

Various things i’ve found useful for my projects using raspberry pi’s, covers things from turning the red light off on the camera to kiosk mode for Chrome. Most of these were initially done under Raspbian - Jessie and may not work uner the latest Buster.

Everything here can be downloaded in the original org-mode format: Snippets of code because of the way hugo interprets org files i’ve had to save it with a txt extension for the link to work. If you want to view the file in emacs/org then simply change the extension to org instead of txt or copy and paste.

Working with files

• read csv and create an array variable

  So the following tries to open a csv file and store in the array SensorValues the contents of each row, if it fails to open the file it simply stores an arbitrary value

  python code snippet start

  # read in stored values & initialise preset values
  import csv
  try:
      with open('/tmp/tmpvalues.csv', 'r') as csvfile:
          fileRead = csv.reader(csvfile, delimiter=',')
          for row in fileRead:
              SensorValues = [float(x) for x in row if x != '']
  except:
      SensorValues = (
          66.00,
          66.00,
          66.00,
          66.00,
          66.00,
          66.00,
          66.00,
          66.00,
          66.00,
          66.00)

  python code snippet end

• credential file

  If you dont want to store your login details in a python script, for example if you want to share that script you dont want to give people you password do you? So you can create a file credentials file eg

  emacs -nw credentials.py

  Then type in the following;

  python code snippet start

  # email login details
  em_login = {
      'smtpdata': 'smtp.server.address',
      'login': 'login.address',
      'password': 'login.password',
      'toemail': 'send.to.email.address'
  }
  # initial state details
  in_login = {
      'login': 'login.address',
      'password': 'login.password',
      'accesskey': 'access.key',
      'bucketname': 'monitorhome',
      'bucketkey': 'bucket.key'
  }

  python code snippet end

  now call this file as a module in the main code and assign to your chosen variable

  python code snippet start

  import credentials
  
  empassword = credentials.em_login['password']
  inpassword = credentials.in_login['password']
  
  print("email password:", empassword)
  print("initial password:", inpassword)

  python code snippet end

• convert windows CR (carriage returns) to linux

  sed -i 's/\r//' filename

  Use with care it could destroy your file, it might be better to the dos2unix utility

PiDisplay

Notes on using the offical pi touch screen

• rotate official display

  Useful if the display case you’ve bought has a fixed orientation;

  edit your /boot/config.txt file, and add the following line:

  lcd_rotate=2

• onscreen keyboard

  You can install an onscreen keyboard by;

  sudo apt-get install florence

  or

  sudo apt-get install matchbox-keyboard

  then reboot, to access the keyboard click on menu/accessories/keyboard

• get backlight status

  Weirdly (at least i think so) it’s 0 for on and 1 for off and script must be run as root

  python code snippet start

  #!/usr/bin/env python3
  # gets current backlight state
  file=open('/sys/devices/platform/rpi_backlight/backlight/rpi_backlight/bl_power','r+')
  current_status=int(file.read(1))
  
  print(current_status)

  python code snippet end

• kiosk mode

  Kiosk mode runs your internet browser full screen useful for setting up a display system. Modify the /etc/xdg/lxsession/LXDE/autostart file or if using the NOOBS installation /etc/xdg/lxsession/LXDE-pi/autostart

  bash code snippet start

  @lxpanel --profile LXDE-pi
  @pcmanfm --desktop --profile LXDE-pi
  @xscreensaver -no-splash
  @point-rpi
  
  @xset s noblank
  @xset s off
  @xset -dpms
  
  @chromium-browser --noerrdialogs --kiosk http://127.0.0.1:5000 --incognito --disable-translate

  bash code snippet end

  BE AWARE if the following file exists then it overrides any other files so the @chromium command must go in here.

  nano .config/lxsession/LXDE-pi/autostart

  so edit it to show the line;

  @chromium-browser --noerrdialogs --kiosk http://127.0.0.1:5000 --incognito --disable-translate

  so my file reads;

  bash code snippet start

  @lxpanel --profile LXDE-pi
  @pcmanfm --desktop --profile LXDE-pi
  @xscreensaver -no-splash
  @point-rpi
  @chromium-browser --noerrdialogs --kiosk http://127.0.0.1:5000 --incognito --disable-translate

  bash code snippet end

Audio

• Enabling Audio Output

  By default, the RPi audio output is set to automatically select the digital HDMI interface if its being used, otherwise the analog audio output. You can force it to use a specific interface via the sound mixer controls. amixer allows command-line control of the mixer for the ALSA driver.

  You can force the RPi to use a specific interface using the command amixer cset numid=3 N where the N parameter means the following:

  • 0=auto
  • 1=analog
  • 2=hdmi

  Therefore, to force the Raspberry Pi to use the analog output:

  amixer cset numid=3 1

• How to play Internet radio on your Raspberry PI (mpd/mpc)

  first make sure your audio is working, using the ALSA package

  install the mpd and mpc packages:

  sudo apt-get install mpd mpc

  change the permissions of mpd (just to make sure):

  sudo service mpd stop sudo chmod -R g+w /var/lib/mpd sudo chmod -R g+w /var/run/mpd

  make a change to the mpd config file /etc/mpd.conf

  sudo nano /etc/mpd.conf

  Note all the sites i visited suggested that it was simply commenting OUT the line:

  bind_to_address "localhost"

  however i had many issues and nothing seemed to work until i had the conf file set as follows;

  shell code snippet start

  # bind_to_address "localhost"
  bind_to_address "127.0.0.1"
  port "6600"

  shell code snippet end

  shutdown/reboot your Raspberry PI after it’s up and running again add an Internet radio URL, for instance:

  • mpc add http://icecast.omroep.nl/3fm-bb-mp3

  to start playing the stream type:

  • mpc play

  The other thing to be aware of is you may need to download the radio stations m3u playlist file and open it to extract the direct URL of the stream (i had to) so the stream i needed was;

  http://stream4.nadaje.com:11986/prs

  then save that into MY OWN m3u playlist for for the MPD daemon to work.

• python check if mpc is playing

  python code snippet start

  from mpd import MPDClient
  
  client=MPDClient()
  client.idletimeout = None          # timeout for fetching the result of the idle command is handled seperately, default: None
  client.connect("localhost", 6600)  # connect to localhost:6600
  print(client.mpd_version)
  
  if client.status()['state'] in ('play', 'pause'):
      print('Playing')
  else:
      print('stopped')

  python code snippet end

bash

• alias

  for example if you get tired of typing emacs -nw to start emacs without a gui window then add

  alias enw='emacs -nw'

  to the end of your .profile or .bashrc file located at /home or /home/usr

misc

• Display system’s serial support

  dmesg | grep tty

  resulting output resembles;

  bash code snippet start

  pi@raspberrypi:~/xbee $ dmesg | grep tty
  [    0.000000] Kernel command line: dma.dmachans=0x7f35 bcm2708_fb.fbwidth=656 bcm2708_fb.fbheight=416 bcm2708.boardrev=0x3 bcm2708.serial=0xf83a1e37 smsc95xx.macaddr=B8:27:EB:3A:1E:37 bcm2708_fb.fbswap=1 bcm2708.uart_clock=48000000 vc_mem.mem_base=0xec00000 vc_mem.mem_size=0x10000000  dwc_otg.lpm_enable=0 console=ttyAMA0,115200 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait quiet splash plymouth.ignore-serial-consoles
  [    0.000718] console [tty1] enabled
  [    0.201139] 20201000.uart: ttyAMA0 at MMIO 0x20201000 (irq = 81, base_baud = 0) is a PL011 rev2
  [    0.201529] console [ttyAMA0] enabled
  [    2.333606] systemd[1]: Expecting device dev-ttyAMA0.device...
  [    2.353451] systemd[1]: Starting system-serial\x2dgetty.slice.
  [    2.354181] systemd[1]: Created slice system-serial\x2dgetty.slice.
  [    9.556243] usb 1-1.2: FTDI USB Serial Device converter now attached to ttyUSB0
  pi@raspberrypi:~/xbee $

  bash code snippet end

• nginx gpg key

  The distributed version of nginx is old, if you want to install the newer versions you have to self compile but first you need to take a couple of steps;

  create a file;

  • sudo nano /etc/apt/sources.list.d/nginx.list

  and add the line;

  deb-src http://nginx.org/packages/mainline/debian/ wheezy nginx

  then run apt-get update and you will receive an error stating the signatures cannot be verified, to overcome this you need the nginx keys which you can get via;

  curl -O https://nginx.org/keys/nginx_signing.key && apt-key add ./nginx_signing.key

  now run sudo apt-key update sudo apt-get update

  and you should get no error messages meaning you can now run;

  apt-get source nginx

  to finally get the latest nginx source for building on your pi (set aside quite some time for it to build) and to install use

  sudo dpkg -i nginx_1.9.4-1~squeeze_armhf.deb

• MOTD

  Below MOTD was found somewhere on the net, when i find from where i’ll add a link (its only here in this file so i remember)

  To get something like this every time you log in;

  You need a custom message of the day script, copy the code and place it in /home/pi/.bash_profile

  bash code snippet start

  let upSeconds="$(/usr/bin/cut -d. -f1 /proc/uptime)"
  let secs=$((${upSeconds}%60))
  let mins=$((${upSeconds}/60%60))
  let hours=$((${upSeconds}/3600%24))
  let days=$((${upSeconds}/86400))
  UPTIME=`printf "%d days, %02dh%02dm%02ds" "$days" "$hours" "$mins" "$secs"`
  
  # get the load averages
  read one five fifteen rest < /proc/loadavg
  
  echo "$(tput setaf 2)
     .~~.   .~~.    `date +"%A, %e %B %Y, %r"`
    '. \ ' ' / .'   `uname -srmo`$(tput setaf 1)
     .~ .~~~..~.
    : .~.'~'.~. :   Uptime.............: ${UPTIME}
   ~ (   ) (   ) ~  Memory.............: `cat /proc/meminfo | grep MemFree | awk {'print $2'}`kB (Free) / `cat /proc/meminfo | grep MemTotal | awk {'print $2'}`kB (Total)
  ( : '~'.~.'~' : ) Load Averages......: ${one}, ${five}, ${fifteen} (1, 5, 15 min)
   ~ .~ (   ) ~. ~  Running Processes..: `ps ax | wc -l | tr -d " "`
    (  : '~' :  )   IP Addresses.......: `/sbin/ifconfig eth0 | /bin/grep "inet addr" | /usr/bin/cut -d ":" -f 2 | /usr/bin/cut -d " " -f 1` and `wget -q -O - http://icanhazip.com/ | tail`
     '~ .~~~. ~'
         '~'
  $(tput sgr0)"

  bash code snippet end

  $(tput sgr0)"

• identify usb devices

  create a script with the following and make it executable

  bash code snippet start

  #!/bin/bash
  for sysdevpath in $(find /sys/bus/usb/devices/usb*/ -name dev); do
      (
          syspath="${sysdevpath%/dev}"
          devname="$(udevadm info -q name -p $syspath)"
          [[ "$devname" == "bus/"* ]] && continue
          eval "$(udevadm info -q property --export -p $syspath)"
          [[ -z "$ID_SERIAL" ]] && continue
          echo "/dev/$devname - $ID_SERIAL"
      )
  done

  bash code snippet end

  taken from: https://unix.stackexchange.com/questions/144029/command-to-determine-ports-of-a-device-like-dev-ttyusb0

• mysql

  using mariadb as the main sql server

  logon to sql server: mysql -u root -p

  create database: CREATE DATABASE home;

  now we need at least one table.

  CREATE TABLE temps (recnum int NOT NULL AUTO_INCREMENT, recdate DATE DEFAULT NULL, rectime time DEFAULT NULL, external float DEFAULT NULL, frontroom float DEFAULT NULL, bedroom float DEFAULT NULL, kitchen float DEFAULT NULL,PRIMARY KEY( recnum ));

  now we can see what we’ve created with;

  show columns in temps

  verse code snippet start

  +-----------+---------+------+-----+---------+----------------+
  | Field     | Type    | Null | Key | Default | Extra          |
  +-----------+---------+------+-----+---------+----------------+
  | recnum    | int(11) | NO   | PRI | NULL    | auto_increment |
  | recdate   | date    | YES  |     | NULL    |                |
  | rectime   | time    | YES  |     | NULL    |                |
  | external  | float   | YES  |     | NULL    |                |
  | frontroom | float   | YES  |     | NULL    |                |
  | bedroom   | float   | YES  |     | NULL    |                |
  | kitchen   | float   | YES  |     | NULL    |                |
  +-----------+---------+------+-----+---------+----------------+
  7 rows in set (0.04 sec)

  verse code snippet end

  now to leave the sql server simply type exit;

• access serial port

  when you want python to access the serial port it will if not run as root error out with permission denied. To get round this add your user to the dialout group eg

  sudo adduser <username> dialout

  then logout and log back in, you should now be able to run your python script with using root. To check what groups your user is a member of simply type groups

crontab

• run in background during boot

  The & at the end of the line makes the script run in the background whilst the pi carries on booting @reboot sudo python /home/pi/homeApp/ourhome.py &

• enable cron logging

  By default, the logging for the cron daemon is not enabled in Debian To enable it, open the file /etc/rsyslog.conf via

  sudo nano /etc/rsyslog.conf

  and uncomment the line

  cron.* /var/log/cron.log

• run on reboot

  to run a command on boot i use the following in the crontab file

  @reboot run_command

• cron sleep

  Starting a command on reboot after x seconds

  For some reason my pi would not wait for the wifi network to come online (wait for network on boot is enabled) so my NAS wont connect, to be honest i had other things to do than fault find so as i added an @reboot mount command with a sleep period to ensure the drive was accessible;

  @reboot sleep 10;sudo mount -a

• specifying the crontab editor

  if like me you’ve accidentally set the wrong editor when first using crontab you can specify the editor everytime using the following;

  bash code snippet start

  export VISUAL=nano; crontab -e

  bash code snippet end

  alternatively you can edit the ~/.selected.editor file and change to your chosen editor;

  bash code snippet start

  # Generated by /usr/bin/select-editor
  SELECTED_EDITOR="/usr/bin/nano"

  bash code snippet end

network

• setup new blank image

  before removing the flashed sd card

  create a blank file called ssh

  then create a file called wpa_supplicant.conf with the following;

  ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev update_config=1 country=gb

  network={ ssid=“your_SSID” psk=“your_password” key_mgmt=WPA-PSK }

• setup wifi via command line

  sudo iwlist wlan0 scan

  Open the wpa-supplicant configuration file in nano: sudo nano /etc/wpa_supplicant/wpa_supplicant.conf Go to the bottom of the file and add the following:

  bash code snippet start

  country=gb
  update_config=1
  ctrl_interface=/var/run/wpa_supplicant
  
  network={
      scan_ssid=1
      ssid="testing"
      psk="testingPassword"
  }

  bash code snippet end

  Then re-configure the interface by wpa_cli -i wlan0 reconfigure

• Static or fixed IP address

  add to /etc/dhcpcd.conf

  bash code snippet start

  #Custom static IP address
  interface eth0
  static ip_address=192.168.1.04/24
  static routers=192.168.1.1
  static domain_name_servers=192.168.1.1

  bash code snippet end

  changing eth0 to wlan0 depending on connection type and also remember to use your own choice of IP address/subnet etc

• mail

  Had problems with a cron job and no idea why & at the time had not setup logging and without an MTA [Mail Transport Assistant] i could not see what errors were being given, after reading up i installed postfix

  sudo apt install postfix

  Choosing “LOCAL” during setup, then after a reboot i could use the following to find out what went wrong:

  shell code snippet start

  sudo tail -f /var/mail/<user>

  shell code snippet end

  alternatively you can set up a more capable system and allow your Pi to send mail using your google account

  shell code snippet start

  sudo apt-get install ssmtp mailutils mpack
  sudo nano /etc/ssmtp/ssmtp.conf

  shell code snippet end

  shell code snippet start

  # Config file for sSMTP sendmail
  
  # The person who gets all mail for userids < 1000
  # Make this empty to disable rewriting.
  # root=localhost
  root=your_chosen_address
  
  # The place where the mail goes. The actual machine name is required no
  # MX records are consulted. Commonly mailhosts are named mail.domain.com
  mailhub=smtp.gmail.com:587
  
  # Where will the mail seem to come from?
  # rewriteDomain=gmail.com
  
  # The full hostname
  hostname=yourHOSTNAME
  
  # Are users allowed to set their own From: address?
  # YES - Allow the user to specify their own From: address
  # NO - Use the system generated From: address
  FromLineOverride=YES
  
  UseSTARTTLS=YES
  
  AuthUser=yourEMAIL
  AuthPass=either password or two-factor key

  shell code snippet end

  • TODO - update rqd Example python script for using sSMTP

    sudo apt-get install ssmtp sudo apt-get install mailutils

    root=postmaster mailhub=smtp.gmail.com:587 hostname=raspberrypi AuthUser=AGmailUserName@gmail.com AuthPass=TheGmailPassword FromLineOverride=YES UseSTARTTLS=YES

  • old

    python code snippet start

    #!/usr/bin/python
    # Taken and modified from an example here:
    # http://tombuntu.com/index.php/2008/10/24/server-monitoring-with-python-and-ssmtp/
    
    import subprocess, re, time
    import urllib, urllib2
    
    # email address to use in the to field
    recipient = 'towhomit@mayconcern'
    # email address to use in the from field
    sender = 'fromwhom@sentit'
    # template for the email message
    # first '%s' is recipient, second is sender, third is content
    message = '''To: %s
    From: %s
    Subject: rpiELEC IP: %s
    
    '''
    
    def send_mail(content):
        try:
            ssmtp=subprocess.Popen(('/usr/sbin/ssmtp', recipient), stdin=subprocess.PIPE)
        except OSError:
            print('Error sending mail')
    
        # pass mail to sSMTP client
        ssmtp.communicate(message % (recipient, sender,content))
        ssmtp.wait()
    
    
    data = re.search('"([0-9.]*)"', urllib.urlopen("http://ip.jsontest.com/").read()).group(1)
    send_mail(data)

    python code snippet end

access a network drive

Edit your /etc/fstab file and add the following line (changing the ip address and location of the credentials file to suit your setup);

//192.168.1.1/Drive /media/nas_documents cifs credentials=/home/drakx/.nas_credentials,sec=ntlmv2,uid=1000,gid=1000,iocharset=utf8 0 0

Now create a file called .nas_credentials in your home directory

username=YOUR_ROUTER_LOGIN
password=YOUR_ROUTER_LOGIN_PASSWORD

ssh file system

One trick i didnt learn until far too late was sshfs essentially it mounts your remote system as a folder on your desktop/laptop so instead of saving files then transfering etc you can open and load the remote files and work on them as if local. Excellent for tweaking your python website.

The line of code you need is really simple;

sshfs pi@192.168.1.69:/home/pi home/user/folder/

python ping

need to sudo pip install ping first

import ping, socket
try:
    ping.verbose_ping('www.google.com', count=3)
except socket.error, e:
    print "Ping Error:", e

emacs

• emacs commands/tips

  key command
  M-;	when a region is highlighted pressing M-; will comment out the section
  C-c C-x -	starts a list in emacs with timer, now pressing M-RET will allow notes
  	eg
  	- 0:00:00 :: Now I can start taking some notes.
  	- 0:00:02 :: If I hit M-RET, a new list item is created.
  	- 0:00:06 :: And so on
  org-toggle-link-display	OK not a shortcut but really useful for me once toggled it displays
  	links in their unshortened form which means if a link has a %20
  	in it then the emacs search & replace ~M-shift-% will work
  	(for some reason files i’ve transferred all had link spaces replaced
  	with %20 bloody annoying
  M-x occur	searches your file with regexp & opens a second buffer with all matches

• emacs org-publish

  took me a long time to get this working and i dont use the ctrl c-e P to get it going you have to use alt-x org-publish ret org ret

  elisp code snippet start

  (setq org-publish-project-alist
        '(
          ("org-notes"
           :base-directory "C:/Users/drakx/Documents/org_files"
           :base-extension "org"
           :publishing-directory "C:/Users/drakx/Documents/org_publish"
           :recursive -t
           :publishing-function org-html-publish-to-html
           :headline-levels 4
           :auto-preamble t
           :auto-sitemap t                ; Generate sitemap.org automagically...
           :sitemap-filename "sitemap.org"  ; ... call it sitemap.org (it's the default)...
           :sitemap-title "Sitemap"         ; ... with title 'Sitemap'.
           :language "en"
           :section-numbers nil
           :with-toc t
           :html-preamble t
           )
  
          ("org-static"
           :base-directory "C:/Users/drakx/Documents/org_files/files/"
           :base-extension "css\\|js\\|png\\|jpg\\|gif\\|pdf\\|mp3\\|ogg\\|swf"
           :publishing-directory "C:/Users/drakx/Documents/org_publish/files/"
           :recursive t
           :publishing-function org-publish-attachment
           )
  
        ("org" :components ("org-notes" "org-static"))
        )
  )

  elisp code snippet end

  now all i need to do is test in my work files and on interlinked org files, as of today [2018-08-05 Sun 09:01] i have only tested it on a simple project

camera camera

• Disable red LED

  Edit /boot/config and add the line

  disable_camera_led=1