The Grannophone - Video Telephony Made Easy

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How it started ...

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Hi! I'm Stefan, and I came up with the idea for the Grannophone back in November 2020, during the second Covid-19 lockdown in Germany, informally known as Lockdown Light.

Twitter user Nitek asked in a (since deleted) tweet how he could set up a video conference solution for his grandmother, who happens to have a large TV and broadband internet access, but is completely clueless regarding technology. Lacking any better options at the time, I suggested that he should ditch the TV idea, and buy an iPad instead, so he could use FaceTime with his grandmother. I hated that there wasn't any better solution to this problem, and so I got to work.

Of course, since I have a day job as well as quite a bunch of other real-life responsibilities, the Grannophone is just a hobby, won't be big and professional (sounds familiar?).

... vs. how it's going:

You may wonder why all the other pages here are in German. The reason for this is that development of the Grannophone obviously started in Germany, and I had hoped that keeping everything in German would lower the barrier of entry and thus make it easier for local volunteers to join the project - especially for semi-retired and retired folks that are still fit enough to use a fretsaw and might have some free time on their hands (while roughly 56% of Germans understand English, this skill isn't distributed evenly across age groups - the older they are, the less likely it is that they will be able to understand English). Sadly, this part of my plan failed spectacularly.

As of September 2023, while people will occasionally donate money towards the project, I'm still doing all of the design and assembly work by myself. I think I have most of the case design finalized, what I still need to work on is cable management (how to keep all the connectors in place when someone tugs on a cable vs. how to avoid fraying and squashing cables) and sufficient passive CPU/GPU cooling, to avoid thermal throttling during longer calls. Limited space inside the case and limited amount of available parts make this a challenge, but I'm sure I'll be able to solve both issues.

By the way, if you happen to be a native English speaker with a solid grasp of German (or vice versa), and would like to help translating Wiki content into English, hit me up - while I am fluent in both languages, doing all the translation work myself would take even more of my time away from working on the Grannophone.

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Watch The Explainer Video

There's a 3m:40s explainer video on YouTube - while the audio is in German, if you turn on subtitles, you will be offered native (as opposed to auto-translated) English-language captions in addition to the German ones.

Design Goals

  • must avoid single points of failure, both in the supply chain and regarding support
    • this will never be a commercially viable off-the-shelf, ready-to-use product:
      • small user base
      • development, certification, manufacturing, stockkeeping costs etc.
      • price for a commercial product would need to be so high that the majority of the intended audience wouldn't be able to afford it
    • a single person or a mom-and-pop store would be unable to sustain this as a business model
      • smart buyers will know this and refrain from buying the product
      • the others will end up with expensive electronic waste once the company goes belly-up
    • simple, low-tech design
    • must use generic parts whereever possible

This is why the Grannophone relies on open standards, open protocols, open source software, and a community-based approach. Anyone can pick up and improve on the design, take over development in case I need to step down, ...

  • parts must be available even during a lockdown
    • electronics can be ordered online, so no problem there
    • suitable plastic cases proved to be a problem (they have a tendency to sell out fast, and take months to get back in stock)
    • hardware/home improvement stores were not affected by the lockdown
      • plywood is cheap
      • plywood is available in vast amounts
      • you don't need expensive/special tools to process plywood, and the tools you do need can be bought at the hardware store as well, for less than 100 € in total

This is what makes the Grannophone beginner-friendly. You don't need a tool shed or hobby workshop, you can basically start working right at your kitchen table. That is literally where the first Grannophone prototypes were built, as you can see in the pictures below.

Since early 2023, I am using a lasercutter in a public access Makerspace to speed up prototyping. Access to a lasercutter is entirely optional, though, as the plans work equally well for a hobbyist tinkerer working with a fretsaw.

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The basic idea is to use a single-board computer like the Raspberry Pi, running Linux and a video-capable SIP client that can be remotely controlled via the command line. Linux is open source, SIP is an open standard, so using them matches our design goals.

The hook switch is a microswitch connected to a GPIO pin.

Handsets can be store-bought (either with an audio jack connected to a USB sound card, or with a USB sound card built in), or built from scratch, just like the entire case itself.

For privacy reasons, placing the handset onto the hook switch automatically covers the camera.

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To make it beginner-friendly, no soldering will be required - crimping will be required for most designs, though.

Some designs will incorporate audio amplifiers/DACs, which allow for larger speakers and thus louder ringing sounds as well as hands-free speakerphone operation.

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A monitoring script will listen for events like someone picking up/hanging up the handset, an incoming call notification, etc. and will trigger the corresponding actions (play a dialtone in the receiver, play a ringtone via the speakers, call remote end, answer call when the handset is picked up, etc.).

To make sure malicious callers cannot use the Grannophone to scam your vulnerable family member, Grannophones will not be connected to the public telephone network, but will connect via the Internet, using VPN connections that are unique to your pair of Grannophones, or, in case of larger setups, unique to your family/clan. These VPNs will use Unique Local IPv6 Unicast Addresses, so that you don't shoot yourself in the foot in the long run (with private IPv4 addresses as the default, there would be a rather large risk for address conflicts when families merge through marriage).

The VPN technology will most likely be OpenVPN or WireGuard - again, open standards/open source solutions - but there's a small chance that we might also use Tor (also open source) instead of a classic VPN. Tor has the advantage that it doesn't require fiddling with router configuration, port forwarding, and the like, but on the other hand, Tor has a higher latency, which might or might not be a problem with Video calls - we'll just have to try it out and see. Maybe we'll use Tor as a fallback for administrative access and OpenVPN or WireGuard for the calls.

The simplest setup will consist of exactly one pair of Grannophones - picking up the receiver on one will auto-dial the other, either immediately or after a grace period of a few seconds.

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Of course, more complex designs are possible. For example, a "sidecar" with a speed dial/busy lamp field, or even a rotary dial, if that is what your elderly family member is most comfortable with.

This is the great advantage of basing the Grannophone on a "tinkerer" hardware platform like the Raspberry Pi - devices can be customized to fit the individual needs of the end user without much effort:

Your family member ...

  • ... has limited dexterity, e.g. due to arthritis? Work around this by using a horizontal panel with large, wide-spaced buttons in front of the Grannophone as a speed dial pad (think "Whac-A-Mole" meets Staples "That was Easy!" Buttons).
  • ... has trouble memorizing new things, but still remembers old phone numbers from 30 years ago? Add a keypad or rotary dial, and map the number your family member dials to the current one.
  • ... has poor eyesight? Get them a large TV set and use that instead of the Grannophone's built-in screen, and add audio cues to the speed dial buttons ("To call your sibling, press this button again.").
  • ... suffers from hearing loss? Connect the Grannophone to their hearing aid either via Hearing Induction Loop (Telecoil) or via Bluetooth, depending on the make and model of their hearing aid. Or if they refuse to wear one, use a software equalizer on the Grannophone to amplify the frequencies they are having issues with.

Historic Design Influence

British readers of a certain age may remember a now-defunct on-line service called Prestel. Germany had a similar system called Bildschirmtext, or BTX for short. One particular design of BTX terminal can be seen here - and I can't deny that its shape had a bit of an influence on the Grannophone's case. Since quite a few vintage telephone tech enthusiasts keep noticing the similarities, I figured it was time to let one of my Grannophones play dress-up with an extra keyboard in front of the camera, displaying an archived screenshot from the actual BTX system as well as the Raspberry Pi and Grannophone logos:

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Note that this is not what the device on the Granny side will ever look like. However, a version with a keyboard could be used on the tech-savvy person's side, to ease remote administration.


The Grannophone concept/design is a registered utility model ("Gebrauchsmuster", registration number DE: 20 2021 001 690.2) in Germany, and at the same time it is licensed under CC BY-NC-SA 4.0.

In short:

  • "BY" means you must mention my name and recognize me as the original creator.
  • "NC" stands for "Non-Commercial" - in layman's terms, this means that you're allowed to build as many Grannophones as you like, but you must not make money from it.
  • "SA" means "Share Alike", so any derivative designs you come up with must be released under the same license.

For the full, legally binding license, spelled out in "legalese", see here.

If you want to build Grannophones for yourself, your relatives, and your friends, if you want to give them away for free or only charge for the costs of the raw materials, that's totally fine, in fact, that's exactly what I hope you will do!

If you're a registered non-profit in your jurisdiction, and would like to sell Grannophones for more than the costs of the raw materials, or would like solicit donations from the recipients, you must contact me in advance. There's a good chance I will grant you a permission to do so.

Same goes for volunteer organizations that aren't registered as a legal entity (think some folks that run a local hackerspace/makerspace, but never bothered registering): Contact me in advance, and I'm sure we'll be able to work something out.

It basically boils down to this: As long as you're not making money from it, I won't ask for money from you, either. If you intend to make money from it, but for a good cause, it's likely that I'll waive any license fees, but I still need to be able to approve/deny it on a case by case basis, to protect and defend my intellectual property.

However, if you try to sell kits or ready-to-use Grannophones based on my concept/design for profit, and you don't have a written licensing agreement with me beforehand, be prepared for some costly legal proceedings.

English-Language News Coverage

So far, the Grannophone's only mention on English-language news sites was a feature by Hackaday: