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User Guide

This guide covers day-to-day operation of the gas monitoring system for lab members. For build and setup instructions see the assembly guide and firmware README.

Contents

  1. System Overview
  2. The Grafana Dashboard
  3. Individual Sensor Web Interface
  4. Time Synchronisation
  5. Calibration
  6. Downloading Data
  7. Troubleshooting

1. System Overview

The monitoring network has three tiers:

ESP32 sensor units          Raspberry Pi hub          Grafana Cloud
(one per chamber)    ──►   (GasMonitor WiFi)   ──►   (remote dashboard)
                            InfluxDB (local)

Windows/Linux laptop ──►   (GasMonitor WiFi)
(Minir-5 + K30 1%)

Each ESP32 sensor unit:

  • Measures CO₂ every 1–60 seconds (configurable)
  • Optionally measures O₂ (combined units only)
  • Displays live readings on a 1.47" touchscreen
  • Logs data to an onboard SD card (monthly CSV files, indefinite retention)
  • Hosts its own web interface at 192.168.4.1 when you connect to its hotspot
  • Pushes data to the Raspberry Pi for central monitoring

The Raspberry Pi hub:

  • Broadcasts the GasMonitor WiFi network
  • Receives data from all sensors
  • Forwards to Grafana Cloud (14-day retention)
  • Provides automatic time sync to sensors on connection

The laptop (mixing bottle monitors only):

  • Reads the Minir-5 (orange bottle, 1–5% CO₂) and K30 1% (clear bottle, ambient CO₂) via USB
  • Pushes readings to the Pi via GasMonitor WiFi
  • Displays the Grafana dashboard full-screen for room-level monitoring

2. The Grafana Dashboard

Accessing the dashboard

In the growth room: The laptop displays the dashboard full-screen at all times. No login required.

From your own device:

  • Open the dashboard URL (ask the lab manager for the link)
  • Must be on the university network, university WiFi, or VPN

As a home screen app (recommended):

Chrome (desktop or Android):

  1. Open the dashboard URL in Chrome
  2. Click the three-dot menu → Cast, save and share → Install as app
  3. Click Install — the dashboard appears as an app icon

Safari (iPhone / iPad):

  1. Open the dashboard URL in Safari
  2. Tap the Share button (square with arrow)
  3. Tap Add to Home Screen → Add
  4. Opens as a full-screen app without browser toolbars

What the dashboard shows

  • All sensors displayed as separate panels
  • Mixing bottle sensors (Minir-5 and K30 1%) at the top, colour-coded by bottle colour (orange and clear)
  • Chamber sensors below
  • Up to 14 days of history
  • Adjustable time window using the time picker in the top-right corner of the Grafana page

Dashboard vs local interface

Feature Grafana dashboard Local web interface (192.168.4.1)
All sensors at once ✓ One sensor only
Remote access ✓ Only when connected to sensor hotspot
History 14 days Up to 10,000 readings in browser; full history on SD card
Download CSV — ✓
Calibration — ✓
Settings — ✓
Works without Pi — ✓

3. Individual Sensor Web Interface

Each sensor has its own web interface, accessible by connecting to its WiFi hotspot.

Connecting

  1. On your phone or laptop, open WiFi settings
  2. Connect to the sensor's network — the SSID is the device name (e.g. Bournemouth, Chamber 4)
  3. Open a browser and go to 192.168.4.1

Phone users: disable mobile data if the page doesn't load — your phone may be using mobile data instead of the sensor WiFi.

Reading view

The main page shows:

  • Live CO₂ reading in ppm with a trend arrow (▴ rising / ▾ falling / · stable)
  • Live O₂ reading in % with trend arrow (combined units only)
  • Last calibration date and type
  • A graph of recent readings for the configured window

Graph

The graph shows real timestamps (HH:MM) on the x-axis once the device has been time-synced. The time window is configurable in Settings. Tap the graph area on the device touchscreen to switch between CO₂ and O₂ graph pages (combined units).

Settings

Navigate to Settings in the web interface to change:

Setting Description
Graph window Time period shown on device and web graph (1 min to 96 hours)
Read interval How often the sensor takes a measurement (1s to 30 min)
Device name Shown on screen and used as the sensor ID in Grafana
Location Location tag in Grafana
WiFi SSID The sensor's own hotspot network name
WiFi password The sensor's own hotspot password

WiFi changes require a device reboot to take effect. Make a note of any new credentials before saving.

Calibration log

The web interface shows the three most recent calibration events — type, date/time, and CO₂ reading at the time. A full log is stored on the SD card as cal_log.csv.

4. Time Synchronisation

The sensor hardware has no real-time clock. Time must be provided after each restart.

Automatic (Pi connected — normal operation)

When a sensor starts and connects to GasMonitor WiFi, the Pi automatically provides the current time. No user action required. A green dot appears on the device screen to confirm the Pi connection.

Manual (Pi unavailable)

If the Pi is offline or the sensor is being used away from the growth room, the sensor displays a splash screen:

TIME SYNC REQUIRED
1. Connect to WiFi: [sensor SSID]
2. Open in browser: 192.168.4.1

To sync time:

  1. Connect to the sensor's own WiFi hotspot
  2. Open 192.168.4.1 in a browser
  3. Time syncs automatically from your device — the splash screen clears

Data during unsync period: Readings are still recorded to a fallback.csv file on the SD card. Once time is synced, this file is automatically backdated and merged into the correct monthly log. No data is lost.

5. Calibration

CO₂ sensor (K30) — when to calibrate

Calibrate the K30 if:

  • Readings appear consistently offset from expected values
  • The sensor has been stored for a long period
  • As part of routine quality control

Calibration methods

The most reliable method. Expose the sensor to a gas containing 0 ppm CO₂ and calibrate to zero.

Suitable gas sources available in the growth room:

  • Pure nitrogen (N₂)
  • 21% O₂ / 79% N₂ (0 ppm CO₂) gas mix plumbed into the growth room

Procedure:

  1. Connect the sensor to N₂ or the zero gas mix
  2. Wait for the reading to stabilise — at least 2–3 minutes
  3. Connect to the sensor's web interface and click Calibrate → 0 ppm
  4. Confirm in the dialog
  5. Wait for calibration to complete (~10 seconds)

400 ppm calibration (use with caution)

⚠️ Warning — departmental compressed air line: The compressed air supply takes outdoor air through desiccation and delivers it at approximately 400 ppm CO₂ on average. However, outdoor CO₂ varies diurnally and with atmospheric conditions, and the compression/desiccation process can shift concentrations. The actual concentration at any given moment may be ±100 ppm from 400 ppm. Do not use this supply for 400 ppm calibration without first verifying the concentration independently.

Preferred method — outdoor calibration:

  1. Power the sensor from a USB battery pack or laptop
  2. Take the sensor outdoors, away from building exhausts and busy roads
  3. Allow 5 minutes for the reading to stabilise
  4. Connect to the sensor's web interface and click Calibrate → 400 ppm
  5. Confirm in the dialog

Confirming calibration

After any calibration, allow 2–3 minutes for the reading to fully stabilise, then verify against a known reference.

O₂ sensor (SEN0322) — combined units only

The O₂ sensor does not require calibration via the web interface. If recalibration is needed:

  1. Take the sensor outdoors to clean air (20.9% O₂)
  2. Hold the physical button on the back of the SEN0322 board until the reading stabilises at ~20.9%

Under normal laboratory conditions O₂ recalibration is rarely necessary. The sensor has a lifetime of approximately 2 years — readings drifting consistently low or becoming unstable indicate the cell needs replacement.

Mixing bottle analysers (Minir-5 and K30 1%) — experienced users only

These sensors are calibrated using dedicated Python GUI tools on the laptop. See the laptop bridge README for full instructions. The GasLab software is no longer used.

Important: Stop the relevant pusher script before running the calibration tool, and restart it afterwards.

6. Downloading Data

From the web interface

  1. Connect to the sensor's WiFi hotspot
  2. Open 192.168.4.1
  3. Scroll to Logs
  4. Click Download next to the month you want
  5. A CSV file will download to your device

CSV file format

datetime,uptime_s,co2_ppm[,o2_pct]
2026-05-10 14:23:01,3601,842[,20.91]
  • datetime — UTC timestamp (ISO 8601)
  • uptime_s — seconds since last device restart
  • co2_ppm — CO₂ concentration in ppm
  • o2_pct — O₂ percentage (combined units only)

Storage

Log files are stored indefinitely on the SD card. At a 5-second read interval the card has capacity for over 20 years of continuous data. Files are never automatically deleted.

7. Troubleshooting

Symptom Likely cause Action
Splash screen asking to sync time Pi unavailable at startup Connect to sensor hotspot → open 192.168.4.1
Sensor not in Grafana Not connected to GasMonitor WiFi Check green dot on device screen; check Pi is powered
CO₂ disconnected on screen K30 not responding Power-cycle the sensor; check K30 cable
O₂ shows -- SEN0322 not detected at boot Power-cycle; check VCC is on 5V not 3.3V
O₂ readings drifting low Electrochemical cell near end of life Replace SEN0322 (~2 year lifetime)
Web interface won't load at 192.168.4.1 Not connected to sensor hotspot Connect to sensor WiFi and disable mobile data
Settings not saved after reboot SD card missing or not FAT32 Check SD card is seated; reformat as FAT32 if needed
Missing months in CSV log Device ran without time sync Check SD card for fallback.csv — data may be there, backdated on next sync
Mixing bottle sensors absent from Grafana Laptop powered off or scripts stopped Check laptop is on and logged in; restart pusher scripts if closed
Readings offset after calibration Calibration performed with unstable reading Wait for full stabilisation (2–3 min) and recalibrate
400 ppm calibration gives wrong result Departmental air line CO₂ variation Use outdoor calibration or N₂/zero gas instead