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Rotary Cellphone


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Rotary Cellphone

 

RotaryCell1.JPG

 

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? 

 

  • 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 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 10 increments of resolution instead of just 4.
  • The ePaper display is bistatic, meaning it doesn't take any energy to display a fixed message.
  • When I want to change something about the phones behavior, I just do it.
  • 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.

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 24 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 ATmega2560V microcontroller with an 8MHz external resonator. It's programmed as an Arduino Mega2560. Although the cell tranceiver is an Adafruit FONA 3G, this doesn't 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 2.13" 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:

 

RotaryCellphone_proof_of_principle.JPG

 

Then I thought I'd just stuff it into a 3D printed enclosure. Let's call this v1:

 

RotaryCellphone_v1.JPG

 

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:

 

RotaryCellphone_v2_Innards_Top.JPG

RotaryCellphone_v2_1.JPG

RotaryCellphone_v2_2.JPG

RotaryCellphone_v2_3.JPG

 

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 ATmega2560 microconntroller, v3 uses the ATmega2560V, which is the low-power version of the chip. It's prorammed in the Arduino IDE as though it's an Arduino Mega2560.

 

Top level schematic:

 

RotaryCellphone_Schematic_TopLevel.png

USB bridge:

RotaryCellphone_Schematic_USBBridge.png
This doesn't work. The bastard:
RotaryCellphone_Schematic_VibMotor.png
The layout looks like this. All the real KiCad design files are available in the link above:


RotaryCellPhone_Layout.png

 

Debugging the serial connection to the FONA:

 

P1080634.JPG

 

Note the Rigol MSO1104Z in the background. A WONDERFUL random present from my husband David one year:

 

P1080637.JPG

 

Complete, top down:

 

RotaryCell2.JPG

 

Showing the ePaper display:

 

RotaryCell5.JPG


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:

 

RotaryCell7.JPG


And still have the back available for other messages, or for  contacts lists, etc:

 

RotaryCell_ePaperMessage.JPG


Another view: 

 

RotaryCell3.JPG

 

RotaryCell1.JPG

 

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Good luck carrying that round in your pocket

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