Build Guideintermediate

Armachat LoRa Doomsday Communicator

Open-source off-grid LoRa QWERTY communicator for long-range text messaging without infrastructure. Features automatic message resending, contact management, and 4+ km range. Winner of Hackaday Prize 2020.

Boards:ESP32-S3
Firmware:ArduinoMeshtastic
Use Cases:Mesh NetworkingPortable DeviceEducation

Overview

Armachat is an open-source, battery-powered LoRa communicator created by Peter "Bobricius" Misenko. It enables text-based wireless messaging over long distances (tested up to 4.3 km) without any reliance on cellular networks, WiFi, or internet infrastructure. The project won 2nd place (Best Design) at the PCBWay 3rd PCB Design Contest and a Bootstrap Award at Hackaday Prize 2020.

Hardware

The original Armachat uses a compact, hands-solderable design with minimal active components:

  • MCU: SAMD21E18 (Arduino Zero-compatible, TQFP32 package)
  • Display: 1.8" TFT LCD (128x160, ST7735)
  • Radio: RFM95 LoRa module with configurable power and spread factor
  • Input: 30-key QWERTY keyboard (5x6 matrix)
  • Power: 18650 Li-ion battery with charging support
  • Optional: DS3231 RTC, GPS module, environmental sensors
  • Storage: 8MB SPI flash for message history

Firmware Features

The custom Arduino-based firmware (open-source on GitHub) provides:

  • Message composition with broadcast and direct messaging
  • Background message reception and storage
  • Contact list with auto-updated remote names
  • Message delivery confirmation
  • Intelligent automatic resending of undelivered messages when stations reconnect
  • Configuration menu for radio parameters (frequency, spread factor, power)
  • Uses only ~20% of flash memory

Meshtastic Compatibility

Later Armachat variants (including the TrackSenger) added Meshtastic firmware support, enabling integration with the broader Meshtastic mesh network ecosystem.

License

Released under CC0-1.0 (public domain).

Resources