I'm Building a Phone

For a couple years I've flirted with the idea of making my own phone. It started as a joke, but has become a real area of design, research and experimentation for me.

Why?

Privacy - Everything about the mobile phone reveals all kinds of data on it's user. To name a few weak points: Cell networks are built on inherently insecure protocols, apps sending third parties your sensitive information to be sold to cops, and mobile carriers often leaking call/text records. An open sourced, privacy focused device would allow the user a better understanding of where their data is going and more granular control over it.

Disconnection - Despite being someone who considers themselves pretty disconnected, I find my smartphone to be exhausting. I'm constantly battling the urge to check it, either refreshing my email or popping onto Instagram and/or Mastodon to scroll when my mind is idle. During the pandemic I made a hard effort to get a dumb flip phone but found it difficult due to the depreciation of 3G networks in the US. The flip phones that were still being manufactured seemed to mostly be running a flavor of Android, which brought me back to the privacy point.

Education - I personally know very little about mobile networks and how they operate, along with RF based hardware/PCB design. This project is going to allow me to interface with lots of new concepts & technology that I previously wouldn't have!

Long Term Project Goals

This is going to be a long term effort as I handle the complexity of the project along with the learning curve. Some big things that'd be cool to accomplish:

Building of a low-cost and easy to re-create development platform for mobile networks
Making a fun, hackable mobile phone with some interesting capabilities
Documenting and sharing my learnings along the way for others to pick up and build on

Being realistic about the scope of this project, I'm pretty content if I realize it isn't feasible and drop it after a while. As it stands, I'm pretty excited about it moving forward though.

SIM7600 Breakout Board v0.1

The first step in getting this phone project rolling was creating a development board based around the SIMCom SIM7600 and graciously PCBWay offered to sponsor the fabrication of the PCBs (see below for more info)! The SIM7600 is a modem that can connect to 4G, send texts, utilize GPS and even make calls. The features of the v0.1 development board are:

All antennas (main, aux, GPS) are broken out into external U.FL antenna receptacles
USB-C 2.0 receptacle for USB interfacing (not powering)
Nano SIM card slot
Headphone jack for listening to phone audio, on board mic for sending phone audio
UART, I2C, & SPI voltage shifter to allow for more devices to utilize with the SIM7600's 1.8V interfaces
30 labeled pins spaced at 2.54mm/0.1in to allow for easy breadboard placing
Indicator LEDs

Next Steps

This is very much just the beginning, I'm currently in the process of debugging the v0.1 breakout board and have started designing a v0.2 correcting issues as I find them. After this is functional using a Raspberry Pi for the brains, I'll likely start to look for embedded Linux solutions and repackaging the SIM7600 so it begins to take more of a phone form factor, along with maybe some old blackberry keyboards (?) and a display.

PCBWay Review

PCBWay sponsored the PCB fabrication for this project with the agreement that I give an honest review afterwards. I can say once again that the quality of these boards was fantastic! All of the soldering was done by hand and when working with 0203 packages (only a few human hairs wide!) a quality made PCB is critical, especially with good plating. I found these PCBs to be a pleasure to work with. The only thing that could've been slightly improved was the silkscreen quality, but with how small my text was I realized issues were likely. Despite that the silkscreen text is still completely legible!

Very grateful to the wonderful folks at PCBWay for being a continuous supporter of these projects!