LoRa Messenger – Off-Grid Texting with Open Hardware

LoRa Messenger is a mobile app (Android/iOS) that enables text messaging over long distances (up to 10km) without cellular or internet connectivity, using LoRa radio transceivers attached via USB-C or Bluetooth. The app pairs with an open hardware dongle (design files on GitHub) that costs under $20. It creates a peer-to-peer mesh network where each phone acts as a relay, forwarding messages to extend range. The app features encrypted messaging, group chats, and location sharing. It's designed for hikers, disaster relief, and communities with poor connectivity.

The entire project is open source—both the mobile app code and the hardware schematics, PCB layouts, and firmware are released under a copyleft license. The goal is to democratize long-range, decentralized communication. While similar to existing proprietary solutions like Garmin inReach or the open-source Meshtastic project, LoRa Messenger focuses on simplicity: the dongle is little more than an ESP32 and a LoRa module, and the app is a straightforward messaging client that can be built by any competent hobbyist.

During natural disasters, cellular networks fail. In remote areas, there's no signal. Existing solutions like satellite messengers are expensive and proprietary, or they require existing infrastructure. People need a low-cost, open, and decentralized way to communicate without relying on any centralized provider. The itch: a portable, affordable, and hackable device that turns your phone into a long-range radio for text, without monthly fees or network dependency.

• Develop a cross-platform mobile app using Flutter.
• Design an open source LoRa dongle with ESP32 and SX1278 module, with 3D-printable enclosure.
• Implement mesh routing protocol (modified flooding with TTL and deduplication).
• Support text messaging, group chats, and file sharing (images up to 100KB).
• Achieve 10km line-of-sight range.
• Keep total hardware cost under $20.
• Security: end-to-end encryption with Curve25519.
• Publish all schematics, code, and app under GPL v3.

• Not a replacement for internet messaging; limited to text and small files.
• Not aiming for voice or video.
• Not a platform for high-throughput data; designed for low-bandwidth.
• Not for commercial sale; it's a DIY community project.
• Not supporting LoRAWAN or existing network infrastructure—pure peer-to-peer mesh.

• Mobile App: Flutter (Dart), Bluetooth Low Energy (BLE) and USB serial libraries.
• Hardware: ESP32 microcontroller, SX1278 LoRa module, USB-C port, 3D-printed case, LiPo battery.
• Firmware: Arduino-based, using LoRa driver libraries, custom mesh protocol.
• Mesh Protocol: Custom simple flooding with acknowledgment and deduplication.
• Encryption: NaCl (libsodium) for end-to-end encryption.
• File sharing: gzip compressed, base64 encoded over LoRa packet chunks (max 255 bytes per packet).

The system has three layers: Hardware dongle <-> Mobile app <-> User. The dongle communicates with the app via BLE (for simplicity) or USB serial (for reliability). The app handles UI, message persistence, and encryption. The dongle handles LoRa radio transmission and reception, and runs a simple mesh relay protocol. Each message is encrypted on the source phone, sent to dongle, then broadcast on LoRa. Other dongles receive and relay if not the destination. The app on the destination decrypts. For mesh routing, each node maintains a neighbor table and uses a simple flooding algorithm with time-to-live (TTL) to limit hops. Messages are acknowledged by the destination; if no ack is received, the source may retry.

• LoRa bandwidth is very low (~250 bps actual), so large messages may take minutes.
• BLE latency and connection instability can cause message loss.
• Regulatory compliance for LoRa frequencies (ISM band, but power limits vary by country).
• Community adoption requires hardware assembly skills; not everyone will build a dongle.
• Battery drain from constant listening can be significant; need power-saving modes.

• Should the phone-dongle connection be BLE or USB? BLE is wireless but slower and less reliable; USB is simpler but tethering is less convenient.
• Mesh routing: simple flooding vs. more efficient protocols like AODV? Flooding is robust but may cause congestion.
• How to handle message delivery confirmation in a mesh? Hop-by-hop or end-to-end ACK?
• Should we support store-and-forward for temporary network partitions?
• How to handle frequency hopping to avoid interference?

The project was planned during a hackathon but the team disbanded after the event. The hardware design was prototyped and basic firmware worked, but the mobile app integration was never completed due to lack of time and shifting priorities. It remains a solid concept that could be revived if a motivated group picks it up.

The app could also include GPS location sharing over LoRa. A future milestone could be organizing community field tests. The project is heavily inspired by Meshtastic but aims for a simpler, cheaper, and more mobile-focused implementation.