Eva Herrada's Do-It-Yourself LoRa Messenger Uses Adafruit Feather RP2040 with RMF95 Boards, Signal
Using a pair of Hoperf RFM95-equipped RP2040 development boards, this end-to-end encrypted communication system works without wires.
Eva Herrada has penned a guide to turning an Adafruit Feather RP2040 RFM95 into a LoRa-based radio bridge for desktop or laptop computers — "because how bad of an idea could rolling your own security really be?"
"The goal with this project is to demonstrate a way to add another layer of distance between two people messaging on Signal by using LoRa radios as a transport mechanism," Herrada writes of the guide, referring to the popular end-to-end encrypted messaging service. "It's also a good demo of how to use our Feathers as 'peripherals' for a desktop computer. We also show how to send messages encrypted with AES (but without including who the sender or receiver are)."
The core of the project is the Adafruit Feather RP2040 with RFM95 LoRa Radio, a spin on the company's dual-core Raspberry Pi RP2040-based Feather boards which adds a Hoperf RFM95 LoRa transceiver and supporting circuitry onto the board to turn it into what the company calls a "RadioFruit." Although boasting general-purpose input/output (GPIO) pins and a STEMMA QT connector like radio-free Feather boards, Herrada's project focuses on its use as a USB peripheral for wire-free communication — meaning that, to follow along, you'll need two of them.
The project is written in CircuitPython, the educationally-focused MicroPython fork, and uses the command-line interface version of Signal, signal-cli, on the desktop side. "This [software] isn't necessary for the project to work," Herrada notes, "but if you want to integrate it into Signal you will need to do it."
When configured as per Herrada's instructions, the two radios communicate wirelessly over surprisingly long distances — and their communications are encrypted using a shared secret key. The hard cryptographic work, to be fair, is handled by Python programs and the Signal command-line app running on the desktop — but the project is a great demonstration of how a USB-connected Feather can act as a peripheral device for communications and more.
The full guide is now available on the Adafruit Learn portal; the Adafruit Feather RP2040 with RFM95 is available to purchase from the Adafruit store at $29.95 — but remember you'll need two to complete the project as-written.