Rotary Cellphone
Why a rotary cellphone? Because in a finicky, annoying, touchscreen world of hyperconnected people using phones they have no control over or understanding of, I wanted something that would be entirely mine, personal, and absolutely tactile, while also giving me an excuse for not texting.
The point isn’t to be anachronistic. It’s to show that it’s possible to have a perfectly usable phone that goes as far from having a touchscreen as I can imagine, and which in some ways may actually be more functional. More functional how?
- When I want a phone I don’t have to navigate through menus to get to the phone “application”. That’s bullshit.
- If I want to call my husband, I can do so by pressing a single dedicated physical key which is dediated to him. No menus. The point isn’t to use the rotary dial every single time I want to make a call, which would get tiresome for daily use. The people I call most often are stored, and if I have to dial a new number, or do something like set the volume, then I can use the fun and satisfying-to-use rotary dial.
- Nearlt instantaneous, high resolution of signal strength and battery level. No signal metering lag, and my LED bargraph gives 24 increments of resolution instead of just 4.
- The ePaper display is bistatic, meaning it does not take any energy to display a fixed message.
- The power switch is an actual slide switch. No holding down a stupid button to make it turn off and not being sure it really is turning off or what.
- Real, removable antenna with an SMA connector. Receptions is excellent, and if I really want to I could always attach a directional antenna.
When I want to change something about the phones behavior, I just do it.
So it’s not just a show-and-tell piece … My intent is. to use it as my primary phone. It fits in a pocket .; It’s reasonably compact; calling the people I most often call is faster than with my old phone, and the battery lasts almost 728 hours.
Technical overview:
The rotary mechanism comes from a particular style of Trimline telephone. Trimline phones had a more compact rotary dial than the standard Bell system phones, making it a good choice when keeping the final device as compact as possible is paramount. There are a couple other instances of rotary cell phones floating around the internet, one of which has what looks like a custom tiny rotary dial that needs a stylus to dial, but I wanted this to have a recognizably-classic rotary dial.
The main board uses the ATmega 1080634 V microcontroller with an 8MHz external resonator. It’s programmed as an Arduino Mega 1080634. Although the cell tranceiver is an Adafruit FONA 3G, this does not use the FONA Arduino libraries. Instead the mainboard code sends serial commands (“AT commands”) directly to the FONA over a software serial link. The ePaper display is the Adafruit 2. “Flexible Monochrome eInk display using Jean-Marc Zingg’s GxEPD2 library.
The board was fabbed by pcbway.com in China but was populated by hand (including the .5mm pitch footprint for the ATmega chip). Had to do some odd things to make everything fit perfectly in the casing (slanted header for FONA module, slanted eInk Friend daughterboard, blah blah).
If you want to make this it would be a good idea to send me an email for notes that I haven’t had a chance to document yet.
The code is an ongoing work. Functionality as of this writing is limited, but it makes and receieves calls reliably.
Open source. All design files (KiCad, Arduino code, mecanical STLs) available here . 
Project Progression:
Originally I was intent on making this a quick and dirty project. I laid everything out flat to make a proof of principle phone and used an Arduino Micro as the controller:
Then I thought I’d just stuff it into a 3D printed enclosure. Let’s call this v1:
But this proved hopelessly delicate. Couldn’t open it to fix something without breaking something else. OK, I guess a board layout is warranted. Did that and came up with v2:
It worked but had all sorts of issues. Battery life less than 2 hours. Used the Adafruit FONA 2G, which was a big mistake because I didn’t realize the 2G networks are shuttind down. Tantalizingly close to having the phone I really wanted.
New design again. This is the final / current version. Whereas v2 used the ATmega 1080637 microconntroller, v3 uses the ATmega 01575879 V, which is the low-power version of the chip. It’s prorammed in the Arduino IDE as though it’s an Arduino Mega .
Top level schematic:
USB bridge:
This does work. The bastard:
The layout looks like this. All the real KiCad design files are available in the link above:
Debugging the serial connection. to the FONA:
Note the Rigol MSO Z in the background. A WONDERFUL random present from my husband David one year:
Complete, top down:
Showing the ePaper display:
- The curved ePaper on tha back was a later development in the creative process but it’s now my favorite part. I think of the screen as having two sections … the part that’s facing toward the top of the phone, and the part that’s wholly on the back. In this way I can have relevant messages display on the top part “pager style”, like the most recent missed call:
And still have the back available for other messages, or for contacts lists, etc:
Another view:
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