Raspberry Pi Fleet Observer

A Raspberry Pi as a local MQTT gateway for a fleet of ESP32s: a Mosquitto broker on the Pi, plus a small Python bridge that forwards each MQTT message to Plexus with the source_id parsed from the topic.

Prerequisites

A Raspberry Pi 3B+ or newer running Raspberry Pi OS Lite (64-bit).
Mosquitto: sudo apt install -y mosquitto mosquitto-clients.
An API key from your /dev/keys page.
The ESP32 → alerts hardware (you’ll re-flash it once).

The bridge

Subscribes to plexus/+/+ and forwards each message to Plexus, one client per source so every device keeps its own identity:


import json, os
import paho.mqtt.client as mqtt
from plexus import Plexus
 
MQTT_HOST = os.environ.get("MQTT_HOST", "localhost")
TOPIC = os.environ.get("MQTT_TOPIC", "plexus/+/+")
clients = {}
 
def get_client(source_id):
    if source_id not in clients:
        clients[source_id] = Plexus(source_id=source_id)
    return clients[source_id]
 
def on_message(_c, _u, msg):
    parts = msg.topic.split("/")          # plexus/<source_id>/<metric>
    if len(parts) != 3 or parts[0] != "plexus":
        return
    _, source_id, metric = parts
    payload = msg.payload.decode("utf-8", errors="replace")
    try:
        value = float(payload)
    except ValueError:
        try:
            value = json.loads(payload)
        except ValueError:
            value = payload
    get_client(source_id).send(metric, value)
 
def main():
    client = mqtt.Client()
    client.on_message = on_message
    client.connect(MQTT_HOST)
    client.subscribe(TOPIC)
    client.loop_forever()
 
if __name__ == "__main__":
    main()

Install (run on boot)


python3 -m venv ~/plexus-bridge && source ~/plexus-bridge/bin/activate
pip install plexus-python paho-mqtt
 
cp bridge.py ~/bridge.py
sudo cp plexus-bridge.service /etc/systemd/system/   # systemd unit, restart-on-failure
sudo systemctl daemon-reload
sudo systemctl enable --now plexus-bridge

Verify with sudo systemctl status plexus-bridge and journalctl -u plexus-bridge -f.

Point the ESP32s at the Pi

Re-flash each ESP32 with the BME280_Dashboard sketch:

Uncomment #define PLEXUS_TRANSPORT_MQTT at the top.
Set MQTT_HOST to the Pi’s LAN IP (e.g., 192.168.1.42).
Give each ESP32 a unique SOURCE_ID (esp32-greenhouse, esp32-fridge).
Install one extra Arduino library: PubSubClient by Nick O’Leary.

Each ESP32 publishes plexus/<SOURCE_ID>/<metric> to Mosquitto; the Pi forwards each to Plexus with the right source_id attached.

Tuning knobs

Set in the systemd unit’s environment:

Env var	Default	What it does
`PLEXUS_API_KEY`	(required)	your Plexus key
`MQTT_HOST`	`localhost`	broker host
`MQTT_TOPIC`	`plexus/+/+`	topic filter (devices/metrics)