Skip to content
Communicator Badge

Meshtastic stack

The badge is a real node on a Meshtastic mesh. The on-air format is implemented directly and checked against the values a stock Meshtastic device uses, so packets interoperate.

Protobufs

Section titled “Protobufs”

Message bodies use the official Meshtastic protobufs (Data, Position, User, and Telemetry with device and environment metrics) generated with nanopb. The proto definitions live in components/mesh/proto/meshtastic.proto, and the generated C is in components/mesh/generated/. Field numbers and types match upstream, so the wire bytes are the same.

Received Position packets contribute the node’s location, and also its ground speed and heading, which the Tracker app uses to follow a moving node. Telemetry packets contribute battery level and, when present, environment readings such as temperature and humidity.

Crypto

Section titled “Crypto”

Channels use AES-CTR with the channel pre-shared key. The defaults are pinned and frozen as host tests:

  • The default channel hash for LongFast is 0x08.
  • The 16-byte nonce is packet_id little-endian, then four zero bytes, then from little endian, then four zero bytes. It is the initial big-endian 128-bit counter.
  • The default PSK expands the one-byte shorthand 0x01 to the published 16-byte key.

Channels

Section titled “Channels”

The badge can run several channels at once — a primary plus a few secondaries, each a name and a key. They share one frequency and are told apart by the one-byte channel hash and the key, so a received frame is decoded by trying each configured channel in turn. The channel-decode helper is portable and host-tested. Outgoing messages use the channel selected in the Messages app, and each stored message remembers which channel it belongs to.

Packet format

Section titled “Packet format”

The on-air header is 16 bytes, little endian: to, from, and id as 32-bit values, then the flags byte, the channel hash, next_hop, and relay_node. The default LongFast flags value is 0x63. The LoRa sync word is 0x2B, not the legacy 0x12 the BadgeNet build used.

Received packets are de-duplicated by the pair (from, id). Rebroadcast is opt in and off by default, so the badge behaves as a handheld client rather than a router unless you turn relaying on.

Region and preset

Section titled “Region and preset”

The region and modem preset set the frequency and the spreading factor. Two values are pinned by host tests as a sanity check: EU_868 LongFast resolves to 869.525 MHz, and US LongFast slot 19 resolves to 906.875 MHz.

Receive and transmit path

Section titled “Receive and transmit path”

The DIO1 interrupt signals the radio task, which reads the FIFO, runs the packet through dedup, decryption, and the nanopb decode, then publishes a message on the event bus. The Messages app records it whether or not that app is open.

On transmit the radio task does listen-before-talk with channel activity detection. It waits on DIO1 for the CAD result rather than polling, backs off a bounded number of times, and then sends. This avoids the tight spin that once starved the MicroPython event loop.