Multi-channel electronic-nose measurement board (E-nose)

Projects / Measurement electronics

Multi-channel E-NOSE V2 measurement system

Measurement system for a multi-channel gas-sensor array with high-impedance analog front end, heater control, STM32 firmware, USB exchange and PC GUI.

Task

What had to be solved

The device had to acquire signals from high-impedance gas sensors, control temperature and give the researcher a practical tool for setup, calibration and data recording.

Result

What the project reached

A working measurement platform was assembled: sensor array, analog front end, microcontroller, digital processing, USB protocol, GUI, logging, heater control and calibration work in one practical measurement loop.

Multi-channel electronic-nose measurement board (E-nose): analog front-end test board

Project materials

Photos and working materials

Multi-channel electronic-nose measurement board (E-nose): temperature measurement and calibration with an external pyrometer

Multi-channel electronic-nose measurement board (E-nose) on the customer's test bench

Multi-channel electronic-nose measurement board (E-nose) during heater debugging

Multi-channel electronic-nose measurement board (E-nose), general view with a PC utility for setup and data acquisition in the background

Multi-channel electronic-nose measurement board (E-nose), first version

Multi-channel electronic-nose measurement board (E-nose) during soldering

Multi-channel electronic-nose measurement board (E-nose): shielding and enclosure prototype

Multi-channel electronic-nose measurement board (E-nose): solder-paste application through a stencil

Multi-channel electronic-nose measurement board (E-nose): earliest prototype with visible corrections made by external wiring

Engineering context

Important constraints

17 logical gas channels and two temperature channels.

High-impedance sensors required several transimpedance amplifier ranges.

Heating needed feedback control, PI regulation and temperature slew-rate limiting.

A continuous PC connection over USB CDC was required.

Work done

What was included

Analog front end and measurement-channel switching.

STM32 firmware for ADC/SDADC polling, filtering, calculations and heater control.

Lightweight binary protocol over USB CDC.

Flash storage of settings, LUT and operating parameters.

PyQt6 PC application for graphs, logging and calibration.

Details

Engineering project description

System composition

The project is built around an STM32 microcontroller, a high-impedance analog front end with transimpedance amplifiers, channel switching, temperature channels and a graphical PC application.

17 gas-sensor channels and two temperature channels
selectable gain range for each gas channel
reference-voltage measurements
heater control with temperature feedback

Firmware and PC exchange

The firmware switches measurement channels, reads ADC and SDADC data, applies digital filtering, calculates temperatures and sensor values, controls the heater and transfers a measurement stream to the PC.

A lightweight binary protocol over USB CDC handles commands, status reading, measurement streaming, LUT transfer and configuration storage.

Measurement cycle

The firmware switches channels, collects ADC and SDADC data, filters the measurements, accounts for reference readings and calculates final values. In normal operation the PC data stream runs at 20 Hz while the internal polling logic works faster.

two temperature channels
17 gas-sensor channels
reference measurements
heater state and error flags

Heater control

The heater is controlled directly by the microcontroller. The system uses a user-defined temperature setpoint, temperature slew-rate limiting, PI regulation, an active feedback temperature sensor and a backup temperature channel for monitoring.

Temperature calibration

Temperature-channel calibration uses an external pyrometer, an automatic heating and cooling cycle, measurement accumulation, LUT generation and result review before confirmation. After calibration, the microcontroller converts raw temperature-ADC values to degrees Celsius using the saved lookup table.

Flash-stored configuration

The microcontroller stores the device name, channel gain map, feedback-resistor table, active temperature sensor, PI parameters, temperature LUTs, setpoint, slew limit and other operating parameters in flash memory. After power-off the device keeps its configuration and starts in a predictable state.

PC application

The application connects to the device as a virtual COM port, displays channels on graphs, shows temperatures and errors, changes gain maps and extended parameters, configures heater operation, logs data to CSV and performs temperature-channel calibration.

Practical measurement workflow

The current platform lets the user connect the device to a PC, see a live measurement stream, control temperatures, change channel gains, configure heater operation, save CSV logs, calibrate temperature channels and restore saved configuration. In practice, the project links the full chain: sensor array, analog front end, microcontroller, digital processing, USB protocol, GUI, graphs, logging, setup and calibration.