Logging every packet a LoRa radio hears

I'm mapping the LoRa radios near me. LoRa is a long-range, low-power radio. Meshtastic is firmware that turns cheap LoRa boards into a text-messaging mesh with no Wi-Fi and no cell service. My board is a Heltec V4 on the US band with the LongFast preset.

Why a log

The radio keeps its own list of nodes it has heard, but that list can lose entries when the board is unplugged or restarts. I wanted a record on disk that doesn't forget.

The logger

lora-log is a Python service using the Meshtastic library. It runs under systemd on my travel laptop and restarts if it dies. It writes:

• one JSON line per received packet, to a file per day
• a snapshot of the radio's node list every time it connects

Two small lessons. Use the stable /dev/serial/by-id/... path for the board, not ttyUSB0, which can change between plugs. And the service holds the serial port, so it has to be stopped before the meshtastic command-line tool can talk to the radio.

Here's part of the log from a test with a second node a few meters away:

time      from    type              snr dB  rssi dBm
20:34:52  node B  TEXT_MESSAGE      6.5     -5
20:34:54  node B  ROUTING           5.75    -6
20:36:38  node B  TRACEROUTE        5.75    -9
20:40:52  node B  POSITION          6.25    -15
20:41:29  node B  NODEINFO          5.75    -7

From the real log, October 15. The other node's ID and location are left out.

Next is plotting the positions on a map.