#+TITLE: FAPG DAQ system
#+AUTHOR: Marius PETER
#+DATE: <2026-06-27 Sat>

* Overview

The goal of this project is to deploy a DAQ network at the FAPG.
Sensor nodes periodically send readings to a central DAQ hub.  An
external VPS obtains these readings, and displays them on a web
dashboard.

* Architecture

#+begin_src plantuml :file docs/architecture.png
  @startuml
  title FAPG DAQ - from reading to web dashboard

  actor "Farm user/browser" as Browser

  participant "EZO probe\npH / EC / DO / Redox" as Probe
  participant "Pi Zero 2W\nfapg-daq service" as Zero
  participant "Pi 5\nMosquitto MQTT broker" as Broker
  participant "VPS\nMQTT subscriber service" as VPSSubscriber
  database "Readings database\nSQLite / PostgreSQL" as DB
  participant "VPS\nLive dashboard app" as Dashboard

  == DAQ acquisition ==

  Zero -> Probe : Request UART reading
  Probe --> Zero : Return raw sensor value

  Zero -> Zero : Normalize reading

  == MQTT publication ==

  Zero -> Broker : MQTT PUBLISH\nfapg/daq/<probe>/<node>/reading\nJSON payload

  note right of Zero
  	Example payload:
  	{
  		"schema": "fapg.daq.reading.v1",
  		"node": "fapg-zero-ph-01",
  		"probe": "ph",
  		"value": 7.12,
  		"unit": "pH",
  		"timestamp": "2026-06-27T13:45:00Z"
  	}
  end note

  VPSSubscriber -> Broker : MQTT SUBSCRIBE\nfapg/daq/+/+/reading
  Broker --> VPSSubscriber : MQTT MESSAGE\nreading topic + JSON payload

  VPSSubscriber -> VPSSubscriber : Validate topic and payload\nparse probe, node, value, timestamp

  == Database storage ==

  VPSSubscriber -> DB : INSERT reading
  DB --> VPSSubscriber : OK

  == Live dashboard presentation ==

  Browser -> Dashboard : Open HTTPS dashboard
  Dashboard -> DB : SELECT recent readings
  DB --> Dashboard : Return recent readings
  Dashboard --> Browser : Initial HTML + Chart.js data

  loop live updates
  	VPSSubscriber -> Dashboard : Notify new reading\nWebSocket / SSE / app event
  	Dashboard --> Browser : Push new reading\nWebSocket or Server-Sent Events
  	Browser -> Browser : Append point to Chart.js chart
  end

  @enduml
#+end_src

#+RESULTS:
[[file:docs/architecture.png]]

** Hosts

*** Raspberry Pi Zero 2W

These hosts collect DAQ readings, and publish them via MQTT on the
LAN.

| Pi Zero | Probe |
|---------+-------|
|      01 | PH    |
|      02 | EC    |
|      03 | DO    |
|      04 | ORP   |


*** Raspberry Pi 5

This host brokers MQTT messages sent on the LAN.

*** VPS

This host establishes a VPN connection with the Pi 5 host, subscribes
to all MQTT topics, saves messages to a database, and exposes a
realtime web dashboard available over the internet.