Online user manual

DIY Nitrox Analyser

Set up, calibrate, operate, and troubleshoot the LilyGo T-Display S3 oxygen analyser. Always compare its result with a trusted analyser or known gas before relying on it.

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Important

This is DIY hardware, not a certified commercial analyser. Calibration is not verification. Confirm the displayed O2 percentage, cylinder identity, gas, date, and MOD before every dive, and remove the unit from service if readings drift or disagree.

First use

Set up the analyser

Inspect the build.Check the cell connector, ADS1115 wiring, button, battery polarity, solder joints, strain relief, and gas path before applying power.
Install the firmware.Use desktop Chrome or Edge and the public browser installer. Choose a LilyGo T-Display S3 and use full install for a new or unknown board.
Open the local Web UI.Join NitroxAnalyser-XXXX with the password shown under Menu → WiFi; the factory default is 12345678. Open http://192.168.4.1/.
Complete basic settings.Add the name used on labels, connect home Wi-Fi if wanted, select MOD limits, and pair a supported Niimbot B1 or B21 printer.
Calibrate and verify.Let the cell stabilise in clean air, perform one air calibration, and compare the result with a trusted analyser or known gas before analysing cylinders.

Button controls

Double short press: Print the current valid reading from the main screen.
Hold about 2.5 seconds: Open the main menu.
Short press in a menu: Move to the next item.
Hold about 2 seconds: Select the highlighted item or leave an information screen.

Measurement

Calibrate in clean air

Expose the cell to clean air.Keep it away from exhaled gas, oxygen-enriched gas, engine exhaust, solvents, and confined or poorly ventilated spaces.
Let temperature and signal settle.Wait for the reading and cell millivolts to stabilise. A recent temperature or pressure change can shift a galvanic cell response.
Check sensor validity.Do not calibrate through a disconnected, noisy, weak, out-of-range, or otherwise invalid sensor warning.
Select Calibrate once.From the main display, hold the button, then select Calibrate. The action immediately stores clean air as 21.0% O2; there is no confirmation screen.
Verify independently.Test against a known gas or trusted analyser. If it still disagrees after one careful recalibration, inspect the gas path, cell, ADC, wiring, and environmental conditions.

Pressure limitation: the clean-air target is not automatically corrected for altitude or unusual ambient pressure. Use a suitable verified procedure for your conditions.

Daily operation

Analyse a cylinder

Confirm the analyser is ready.Use a charged battery or stable USB supply, verify calibration, and make sure the displayed sensor state is valid.
Start a gentle, steady sample flow.Use a suitable flow restriction or sampling method. Excess flow or pressure can change the reading and shorten cell life.
Wait for a stable value.Do not record the first moving number. Wait until the O2 reading has settled and check for noise or warnings.
Read the selected MOD values.MOD is calculated from the measured O2 percentage and configured pO2 limits. The displayed calculation does not choose a safe operational limit for you.
Record and cross-check.Confirm the gas, cylinder, date, analyser identity, and planned limit before marking or using the cylinder.

Bluetooth labels

Pair and print with Niimbot

Prepare the printer.Charge and switch on a supported Niimbot B1 or B21, close the cover, load suitable gapped stock, and close other phone-app connections.
Pair it.In the Web UI open Print, scan for printers, choose the correct result, and save it. On Demand is the normal low-power connection mode.
Check label settings.Select the active name and print-label pO2 limit before analysing. Confirm the analyser date and time if the label includes a date.
Print only a stable reading.From the main screen, press and release the button twice quickly; the second release should occur within about 0.9 seconds.
Verify the physical label.Discard partial or unclear output. Compare O2, MOD, name, and date with the analyser before attaching the label to the cylinder.

Activation and updates

Licence the firmware and keep it current

Copy the Device ID.After installation, open the Web UI and copy the 12-character Device ID from the Licence section.
Request a licence.Email the Device ID to hello@nitroxanalyser.com. Online card payment is not enabled yet.
Activate the supplied code.Paste the device-bound code into Activate existing key. Keep a private copy of the code.
Use update-only for normal updates.Update-only preserves calibration, Wi-Fi, printer, names, history, and licence. Use full install only for a new board, recovery, unknown firmware, or a partition-layout change.
Recheck after updating.Confirm the reported version, calibration, known-gas response, and a test label before the next dive.

Fault finding

Common problems

Problem	What to check
Sensor disconnected or invalid	Stop analysis. Check cell seating, polarity, connector, ADS1115 wiring, moisture, cell age, and Diagnostics millivolts. Repair, then calibrate and verify.
Air does not read near 21%	Move to uncontaminated air, stabilise temperature, recalibrate once, then compare with trusted equipment. Remove from service if disagreement remains.
Setup page will not open	Join `NitroxAnalyser-XXXX`, accept the no-internet warning, use `http://192.168.4.1/` rather than HTTPS, and temporarily disable VPN or mobile-data switching.
No printer found	Charge and power-cycle the printer, close its phone app, move it closer, check label stock and cover, then scan again.
Device sleeps in air	The default battery sleep activates after five minutes below 27% O2. Press the button to wake or adjust the separate battery/USB sleep settings.
Update or activation problem	Record the Device ID, firmware version, exact message, and steps. Do not include passwords or licence keys when contacting support.

For deeper fault isolation, use the dedicated Nitrox troubleshooting guide or email hello@nitroxanalyser.com.