Senior citizen-friendly video telephony system with a Raspberry Pi
Autostart All Services
Processes and programs can be started automatically in different ways on the Raspberry Pi. In this example, I will be using a desktop file that starts a number of processes in parallel in the background. The advantage of this procedure is that the LXDE interface starts up completely in the background, and you end up in the graphical user interface after exiting the web browser by pressing the Ctrl+F4 hotkey.
For this example, enter
sudo nano /etc/xdg/autostart/usr_autostart.desktop
to create the autostart file and add the following content:
[Desktop Entry] Type=Application Name=usr_autostart.sh Comment=user defined autostart script NoDisplay=false Exec=/bin/bash /home/pi/usr_autostart.sh
The system reads the usr_autostart.desktop
file when booting the graphical interface and then executes the command entered in the Exec
line. In this case, the system loads the script /home/pi/usr_autostart.sh
, which has the startup commands.
Again you have to create this file manually by typing
nano /home/pi/usr_autostart.sh
and adding the content shown in Listing 3. To allow the system to execute the file, adjust the permissions after saving with
chmod +x /home/pi/usr_autostart.sh
Listing 3
usr_autostart.sh
01 #!/bin/bash 02 ### Turn off the mouse pointer after 5 seconds of inactivity. 03 unclutter -idle 5 04 ### Turn off the screen saver and power saving functions. 05 xset -dpms 06 xset s off 07 xset s noblank 08 ### Turn on the TV and switch to HDMI. 09 echo 'on 0' | cec-client -s -d 1 10 echo 'as' | cec-client -s -d 1 11 ### Update date and time from Fritzbox for email. 12 sudo rdate -4nu -s <192.168.178.1> 13 ### Send email with link that Jitsi has started. 14 sudo echo 'https://meet.jit.si/<MeetID>#config.prejoinPageEnabled=false&config.disableAP=true&config.noisyMicDetection=false&config.video.height.ideal=240&config.video.width.ideal=360' | mail -s 'Jitsi Meeting ID is online' <the.grandson@example.com> 15 ### Start Jitsi meeting in Chromium. 16 chromium-browser --noerrdialogs --disable-crash-reporter --kiosk https://meet.jit.si/<MeetID>#config.prejoinPageEnabled=false&config.disableAP=true&config.noisyMicDetection=false&config.video.height.ideal=240&config.video.width.ideal=360 17 exit
The usr_autostart.sh
file outsources four tasks:
- Turning off the mouse pointer and the screen saver (lines 2-7).
- Turning on the connected TV and switching to the HDMI input (lines 8-10).
- Sending a notification to a specified email address (lines 11-14).
- Starting the Jitsi meeting in the Chromium browser (line 16).
The xset
command from the x11-xserver-utils package, which can be used to turn off the screen saver, among other things, is part of the default installation. To turn off the mouse pointer, install the unclutter package with:
sudo apt install unclutter
The TV device is controlled by the previously installed cec-client
. With a pipe (|
), you can forward the command output with an echo
to the client. For example,
echo 'on 0'
wakes up the device with device number 0 from standby, and
echo 'as' echo 'is'
switches the HDMI input of the Raspberry Pi to active and inactive.
You can set the <MeetID>
in lines 14 and 16 freely. However, when choosing the ID, make sure that strangers do not hijack the video call. A random alphanumeric string such as that output by the command
xxd -l16 -ps /dev/urandom
would be a good choice. Additionally, you have to adjust the IP address of the wireless router in line 12; the same applies to the email address of the recipient of the notification in line 14.
The call to Jitsi in the web browser in line 16 passes a set of parameters:
config.prejoinPageEnabled=false
suppresses a prompt for which username to use when joining the meeting. Without a mouse and keyboard, this would be impossible to answer.config.disableAP=true
disables audio processing, mainly to reduce the load on the Raspberry Pi CPU.config.noisyMicDetection=false
prevents a warning message from appearing as soon as the microphone signal becomes noisy.config.video.height.ideal=240
…=360
reduces the video resolution to save the Raspberry Pi's processor.
You will often read on Internet forums that exit
at the end of a script that runs all the way through is not good style, but when I tried a script without exit
, Chromium failed to start; at the end of the day, the instruction does not do any harm.
Keystroke Shutdown
Now you have established a connection, but a routine is still missing that shuts down the system properly. The grandparents should not have to adjust anything on the Raspberry Pi or the TV.
For this purpose, I drilled a hole in the case for a switch that sits between the processor and the USB ports above the board; some space is available there for the connection cables. After I installed a suitable push button in the housing, I connected it with one cable each to GPIO pins 5 and 9 (GND) to close a circuit when the button is pressed (Figure 2). Connected to pin 5, the button also wakes the Raspberry Pi from sleep mode if the small-board computer is connected to a power supply (Figure 3). This function is integrated at the factory and requires no further configuration [6].
If the Raspberry Pi is running, the button will initiate a shutdown process that switches the HDMI input of the TV back to inactive, which, in turn, usually causes the TV to switch to the last selected channel. Furthermore, you want the Raspberry Pi to shut down the operating system gracefully, which includes exiting Chromium and thus the video conference.
To do this, the system needs to monitor GPIO pin 5 continuously, as performed by the/home/pi/shutdown.py
script (Listing 4). This script needs to be started before the graphical user interface in the existing /etc/rc.local
file with the shutdown entry,
#!/bin/sh -e [...] python /home/pi/shutdown.py & exit 0
Listing 4
/home/pi/shutdown.py
01 # Shutdown script 02 # Waits for LOW at pin 5 03 04 import RPi.GPIO as GPIO 05 import os 06 07 GPIO.setmode(GPIO.BOARD) 08 # GPIO pin 5 as input with signal HIGH 09 GPIO.setup(5, GPIO.IN, pull_up_down=GPIO.PUD_UP) 10 11 try: 12 while True: 13 # Waits for the pin to be connected to GND 14 GPIO.wait_for_edge(5, GPIO.FALLING) 15 # Raspberry Pi signal is turned off at the TV 16 os.system("echo 'is' | cec-client -s -d 1") 17 # os.system("echo 'tx 10:9D:10:00' | cec-client -s -d 1") 18 # Proper shutdown, also of Chromium 19 os.system("shutdown -h now") 20 21 except: 22 GPIO.cleanup()
which should appear in the penultimate line, before the final exit 0
, as shown. Be sure to include the &
at the end of the Python program call; otherwise, the system will wait for the script to finish, which would cause the system to freeze.
Finally, you need to make the Python script executable by typing:
sudo chmod +x /home/pi/shutdown.py
You should also take a look at lines 16 and 17 of Listing 4. According to the specification, the CEC call echo 'is'
switches the HDMI signal to inactive. In combination with my Sony Bravia TV, however, this command did not do what the doctor ordered. The TV continued to display the picture of the Raspberry Pi system fed in over HDMI. Fortunately, deregistering the signal at the TV with a CEC frame injection by calling echo 'tx 10:9D:10:00'
worked.
If you experience issues, try one of the two calls by removing the hash symbol #
in one line and adding it to the other line. Unfortunately, every manufacturer does its own thing when it comes to CEC. Often, CEC only really works reliably with newer TV sets.
Input and Output Devices
To guarantee that the system always outputs audio through the TV and records audio from the microphone built into the webcam, you need to enter the audio devices permanently on the system. To do this, display the input and output devices detected by Raspberry Pi OS with aplay -l
and arecord -l
(Listing 5).
Listing 5
Detected Devices
$ aplay -l List of hardware devices (PLAYBACK) Card 0: b1 [bcm2835 HDMI 1], Device 0: bcm2835 HDMI 1 [bcm2835 HDMI 1]. Sub devices: 4/4 [...] Card 1: Headphones [bcm2835 Headphones], Device 0: bcm2835 Headphones [bcm2835 Headphones]. Sub devices: 4/4 [...] $ arecord -l List of hardware devices (CAPTURE) Card 2: C920 [HD Pro Webcam C920], Device 0: USB Audio [USB Audio]. Sub devices: 1/1 Sub-device #0: subdevice #0
The important parts of this output are the device names that follow the card numbers; in this example, b1 is the HDMI output, Headphones the analog headphone jack on the Raspberry Pi, and C920 the Logitech webcam used in the setup.
Now create the appropriate settings file by typing
sudo nano /etc/asound.conf
and pasting the content from Listing 6. Usually, you will only need to adjust the device name of the webcam microphone in line 9. After a restart, the correct devices should now be selected automatically.
Listing 6
/etc/asound.conf
01 pcm.!default { 02 type asym 03 capture.pcm "mic 04 playback.pcm "speaker 05 } 06 pcm.mic { 07 type plug 08 slave { 09 pcm "hw:<C920>" 10 } 11 } 12 pcm.speaker { 13 type plug 14 slave { 15 pcm "hw:b1" 16 } 17 }
The WebRTC test page [7] should then report no errors, and the audio and video test for WebRTC [8] should output image and sound from the webcam (Figure 4).
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