Picking Up a Phone Call

The receiving side does not need to go through as much trouble because I assume that the children and grandchildren have a PC or smartphone. To receive the call from grandma and grandpa, all they have to do is open the link from the email into a web browser, and the grandparents appear on the screen.

Theory and Practice

During the first field test of the full setup, massive interference in the microphone signal occurred in Jitsi. In a direct test of the microphone and sound card (on the Raspberry Pi and a Windows PC), the errors could not be reproduced, so the hardware is obviously not responsible.

The explanation was too weak a power supply, which was overtaxed by supplying power to the Raspberry Pi, sound card, and webcam. A better power supply quickly provided a remedy; alternatively, the use of a USB hub with its own power supply is also an option.

It turns out that the third generation of the Raspberry Pi is overtaxed by high-definition video telephony. Transferring the picture and sound without interruption proved to be a difficult task. On the one hand, the latency caused a noticeable delay during the call. On the other, the echo and acoustic feedback effects disturbed the sound because I couldn't shield the webcam's microphone against the TV's speakers.

If you don't want to upgrade to a far more powerful Raspberry Pi 4, you can mitigate both issues by reducing the CPU load during the video call – which is why Jitsi is called with the parameters shown in the scripts. The picture and sound quality are not perfect, but good enough.

Sources of Error

In the initial phase with the video telephony system, it quite often happened that my grandparents accidentally switched their Sony TV to standby with the remote control while the Raspberry Pi was still running. After that, setting the HDMI input to inactive did not work as desired because the TV did not know what signal source it had been displaying before the Raspberry Pi. The Raspberry Pi's HDMI input remained the last activated input source, and my grandparents needed help because they did not know how to switch to the TV function on the TV. Disaster: the TV stayed black even after it was switched back on.

The attempt to switch the signal source actively to a TV channel by CEC before shutdown did not succeed. In the worst case, the TV still showed a black screen after switching on, but at least it switched back to a TV channel after starting and shutting down video telephony. Some CEC functions are supposed to control the TV's digital tuner remotely; however, in the setup used here, the call from the Raspberry Pi reported that the command was not recognized.

The Sony's remote control has a button for switching between analog and digital, which can also switch the signal input back to the TV. Fortunately, I could communicate this information by telephone. Happily, my grandparents only make this mistake once in a while and should improve their skills over time. To eliminate this source of error completely, the system would have to be given its own TV set. Smaller devices are available second-hand for just a few dollars.