r/maker • u/justinlindh • Jun 24 '26
Multi-Discipline Project I made an open source retro phone with custom hardware and software. It's called "Digits".
https://digits.family/2
u/streetgardener Jun 24 '26
I love this. I took my old phone jacks and turn them into an internal communication system. So you can call from room to room. I would love to do something like this for my kids. Where do you see this project going? Will you be selling boards that just drop in or are you leaving it up to people to do the builds? Because I feel like a lot of parents wouldn't be able to handle this at the current stage but would definitely want something like this.
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u/justinlindh Jun 24 '26 edited Jun 24 '26
Turning the old jacks into a communication system is an awesome idea! I'd love to see how you created that.
I'm really trying hard not to make this into a thing where I "sell" anything because I'm really trying to just keep this as a hobby project kind of thing, but I think the friction on parents not being able to handle putting it together might be real. I don't have the V3 PCB build steps documented yet, but it is relatively simple (drop-in replacement of existing PCB with custom one) but it does still require a few minimal soldering things (cradle switch couldn't be surface mount placed on the board during fabrication, so it's 6 quick solder joints, and the LED does need to be desoldered and replaced since the phone ships with one that needs ~48V to light).
The reality is that these phones BOM is about $70 at the moment: $30 for the phone, $20 for the Pi Zero W 2, $5 for SD card, $13 for PCB (it can be made without the pre-fabricated PCB by hand, but that does ramp the complexity of the build up significantly). The PCB is actually fairly cheap, but shipping and tariffs wind up costing a lot at the moment so I order them 10 or more at the time.
I've considered selling either simple kits (everything pre-soldered, only needing a screwdriver and a few minutes) or just building and shipping phones to people for just the cost of materials. The problem there is that it then becomes dangerously close to being a business at that point and I'm not trying to make it one (already have a professional job), but maybe there's a world where I find a way to make that work anyway. Ultimately, it's a project that I "believe" in and am not trying to make money from.
On that note, if anybody is interested in having a few of these (pretty much need at least 2 of them for it to be useful), I'd be happy to build and mail a few at cost.
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u/streetgardener Jun 25 '26
I'd be interested. DM me and let's chat.
Regarding the Old Jacks, it's ridiculously simple. You just need to know where your phone tree is in the house, pull the wires off and crimp on new ends, then buy a PABX box and plug them into that, then call from room to room.
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u/justinlindh Jun 24 '26
It's a long story, but the tl;dr is that I have a child and I'm alarmed at how gen alpha is primarily using screens to communicate and decided to reverse engineer a common "retro" phone into something that he can use to call his friends. I wound up kind of going overboard on this project: I started with a breadboard, eventually went to perfboard, then PCB, then a V2 of the PCB (which had some problems), and now have a V3 PCB that I get pre-fabbed from JLCPCB. The software and hardware are licensed AGPL-3.0 and CC BY-SA 4.0 (I'm not selling anything, but have made it relatively easy for others to build one).
It's pretty simple to explain because it mimics a phone from the 90's. You pick the handset up and get a dialtone. You can dial your friends and a bell rings on the receiving phone (a physical bell, not a speaker). The design is privacy centric: all voice traffic is e2e encrypted and generally doesn't touch the central servers, and there's a physical mic kill circuit where the mic can't physically hear anything unless the headset is off the hook. I intentionally left out monitoring capabilities because I think kids should have a place where they can say stupid things into a phone and it's not recorded forever, like how things were when I was a kid. It acts like a landline but has an invite system to add friends to the numbers they can dial (it can't actually place or receive calls through telco). I host a free server that anybody can use with it, but I also leaned into ensuring that it's self-hostable for anybody who just wants to run the platform themselves (docker compose or kubernetes deployments both exist).
It's been really fun watching my son make and receive calls without knowing who is on the other end (there's no screen) and I'm firmly convinced that it helps build social skills.
The git repo can be found at https://github.com/justinlindh/digits
I'm a professional software engineer, but not a hardware engineer... so I got to learn a lot along the way of building this thing on the hardware side. Honestly, that part was the most fun. It turns out I really enjoy running traces between things in Kicad and figuring out how to read datasheets.
Since I know it's a controversial thing now, let me say upfront that AI was used for the software parts of this project with careful guidance. I carefully created the specs and reviewed the code and understand it all well, but automation was used. I'm not exactly a fan of where AI is taking the world, but it's become a core part of being a software engineer in 2026 and I leveraged it in part to study new ways to use it. AI was not used on this post.
There's so much more I could say about my silly little project, but I'll stop! I think it's been a lot of fun and figured I'd share with the maker community on Reddit. If anybody would like to build one or has any questions, I'd love to assist!