Imported from GitHub: bradkim06/gas_nordic · commit 3c07391 · license Apache-2.0

Description

gas sensing iot device(nrf52832)

README

Industrial Gas Monitor Firmware (nRF52832 + Zephyr)

Firmware version 1.0.2 for HHS's portable industrial gas monitor. The application runs on a custom nRF52832 board, measures multiple gases, and transmits real-time readings over Bluetooth® Low Energy. Environmental data is fused with the Bosch BSEC2 library to provide indoor air-quality indicators in addition to electrochemical gas concentrations.

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Table of contents

1. Key features
2. Hardware overview
3. Supported measurements
4. Firmware architecture
5. Build and flash
6. Bluetooth protocol
7. Calibration & persistent settings
8. Reference tables
9. License

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Key features

• Multi-gas sensing – Electrochemical front-end for oxygen and a selectable toxic gas channel (NO₂, CO, H₂S, Cl₂, NH₃, etc.) with temperature compensation and dynamic calibration algorithms.【F:src/gas.c†L1-L212】
• Environmental monitoring – Integrated BME68x support with Bosch BSEC2 fusion to derive temperature, humidity, pressure, IAQ, equivalent CO₂, and VOC indices. BSEC state is saved to flash for consistent long-term behavior. 【F:drivers/bme68x_iaq/bme68x_iaq.c†L40-L460】【F:src/settings.c†L1-L137】
• Bluetooth LE connectivity – Custom 128-bit GATT service publishes semicolon-delimited measurements every 10 seconds and accepts configuration commands from a companion application.【F:src/bluetooth.h†L5-L45】【F:src/bluetooth.c†L520-L585】
• Robust low-power platform – Built on Zephyr RTOS (nRF Connect SDK v2.4.2) with watchdog, power management, persistent storage, and board-specific optimizations.【F:prj.conf†L1-L110】

Hardware overview

• Target SoC: Nordic Semiconductor nRF52832 (ARM® Cortex®-M4F, BLE 5).
• Custom board definition: boards/arm/hhs_nrf52832 (schematic and layout included in doc/).【F:boards/arm/hhs_nrf52832/hhs_nrf52832.yaml†L1-L53】
• Latest hardware pack: doc/gas_nrf52832_rev1.0.1.pdf with matching schematic doc/gas_nrf52832_sch_rev0.1.0.pdf.
• Peripheral highlights:
  • Bosch BME688/BME680 environmental sensor on I²C.
  • Dual-channel electrochemical sensor front-end via SAADC.
  • Battery gauge through voltage divider + ADC.
  • RGB status LED and watchdog support.

Supported measurements

Domain	Reported values
Electrochemical gas	Oxygen concentration (%VOL) and one selectable toxic gas in
	ppm, both temperature compensated and filtered.【F:src/gas.c†L1-L212】
Environmental	Temperature (°C), relative humidity (%RH), barometric
	pressure (Pa), IAQ score, equivalent CO₂ (ppm), and breath
	VOC index via BSEC2.【F:drivers/bme68x_iaq/bme68x_iaq.c†L40-L460】
Power	Battery percentage derived from loaded voltage profile.
BLE telemetry	Timestamped payload streamed every 10 seconds (default).

Firmware architecture

The firmware is organized into cooperative Zephyr threads and kernel events. A high-level flow is shown below:

---
title: Portable Gas Monitor Firmware Flow
---
stateDiagram-v2
    direction TB
    [*] --> ZephyrRTOS
    ZephyrRTOS --> BME68x_BSEC
    ZephyrRTOS --> Electrochemical_ADC
    ZephyrRTOS --> BluetoothLE

    state ZephyrRTOS {
        state BME68x_BSEC {
            direction LR
            initBSEC --> readEnvironmental : 3 s
            initBSEC --> computeIAQ : 60 s
        }
        state Electrochemical_ADC {
            direction TB
            sampleADC --> tempCompensation
            tempCompensation --> gasConversion
            gasConversion --> dynamicCalibration
        }
        state BluetoothLE {
            direction LR
            initialize --> advertise
            advertise --> connected
            connected --> notifyData : 10 s
        }
    }

Key modules reside in src/ (application logic), drivers/bme68x_iaq/ (BSEC2 integration), and lib/ (Bosch libraries). Threads communicate via Zephyr events for deterministic BLE publishing and alarm handling.

Build and flash

1. Install prerequisites
   • nRF Connect SDK v2.4.2 with the Zephyr toolchain, west, and SEGGER J-Link tools.
   • Bosch BSEC2 library files are already provided under lib/.
2. Fetch the source

   git clone https://github.com/<your-org>/gas_nordic.git
   cd gas_nordic
   west init -l .
   west update
   

3. Build

   west build -b hhs_nrf52832 .
   

   The output image is generated at build/zephyr/zephyr.hex.
4. Flash

   west flash
   

   or, to use Nordic's command-line tools directly:

   ./flash.sh
   

   (flash.sh performs a chip erase and programs the generated HEX via nrfjprog).【F:flash.sh†L1-L5】

Bluetooth protocol

The device exposes a proprietary 128-bit primary service (0000FFF0-0000-1000-8000-00805F9B34FB).【F:src/bluetooth.h†L9-L26】

Characteristic	UUID	Properties	Description
Measurement	0000FFF1-0000-1000-8000-00805F9B34FB	Notify	Periodic payload O2;Gas;Battery;Temp;Pressure;Humidity separated by semicolons, integers scaled as <val1>.<val2> where applicable.【F:src/bluetooth.c†L536-L576】
Command	0000FFF2-0000-1000-8000-00805F9B34FB	Write	ASCII commands for calibration and configuration: O2=<percent>, NO2=<ppm>, BT=<name>.【F:src/bluetooth.c†L60-L124】

Notifications are issued when a connection is active and the client enables CCCD. Each update corresponds to the latest sensor snapshot and is throttled to the configured 10 s publishing interval.

Calibration & persistent settings

• Dynamic calibration continuously refines oxygen and toxic gas baselines by monitoring derivative stability, expected ranges, and board temperature. Manual calibration can be triggered by writing to the command characteristic as described above.【F:src/gas.c†L1-L212】【F:src/bluetooth.c†L60-L124】
• Persistent storage uses Zephyr's settings/NVS subsystem to retain BSEC state, sensor calibration voltages, and the advertised Bluetooth name across reboots.【F:src/settings.c†L1-L200】
• Battery reporting samples SAADC channels and converts them into a percentage using empirically tuned thresholds (see src/battery.c).

Reference tables

Oxygen concentration guide

Category	Concentration range	Notes
High oxygen	> 24 %	Elevated combustion risk.
Normal air	20.9 %	Nominal breathable atmosphere.
Elevated exposure risk	19.5 – 20.9 %	Monitor for dilution hazards.
Low oxygen	16 – 19.5 %	Impaired cognition and physical performance.
Anoxic	< 16 %	Life-threatening within minutes.

Indoor air quality (IAQ) interpretation

IAQ index	Air quality	Suggested action
0 – 50	Excellent	None required.
51 – 100	Good	None required.
101 – 150	Lightly polluted	Ventilate if convenient.
151 – 200	Moderately polluted	Increase ventilation with clean air.
201 – 250	Heavily polluted	Identify contamination source, improve airflow.
251 – 350	Severely polluted	Restrict access, maximize ventilation.
> 351	Extremely polluted	Avoid occupancy until levels normalize.

CO₂ comfort levels

Level	Description	ppm
😆	Healthy outdoor reference	350
😀	Healthy indoor climate	600
🙂	Acceptable indoors	800
🙁	Ventilation desirable	1000
😩	Ventilation necessary	1200
😡	Noticeable health effects	2000
⚠️	Dangerous for prolonged exposure	5000

VOC hygiene guidance

Rating	Recommendation	Exposure duration	TVOC (ppm)
Excellent	Target value	Unlimited	0 – 0.065
Good	Ventilation recommended	Unlimited	0.065 – 0.22
Moderate	Increase ventilation, inspect for sources	< 12 months	0.22 – 0.66
Poor	Intensify ventilation, locate emission sources	< 1 month	0.66 – 2.2
Unhealthy	Immediate ventilation required	Hours	2.2 – 5.5

License

Distributed under the terms of the MIT License. Bosch BSEC2 library usage is subject to its proprietary license (see lib/Bosch-BSEC2-Library).