Senior Design · Fall 2025 – Spring 2026

VOC Breath Sensor Platform for Real-World Data Acquisition

Breathalyze-BG is a portable embedded platform designed to collect exhaled volatile organic compound (VOC) sensor data for research into correlations between breath biomarkers and blood glucose. The completed prototype combines custom electronics, embedded firmware, a guided user interface, wireless data export, and an airflow-focused enclosure.

Explore the Hardware View Test Results Project Files

Embedded Systems Custom PCB Design VOC Sensors Digital Data Export CAD & CFD

Completed Breathalyze-BG handheld VOC data acquisition prototype powered on

5Figaro VOC sensors

4Custom PCBs

2 minWarm-up period

~50Tests per charge

128 × 52 × 61Final dimensions, mm

CAD + CFDAirflow-guided enclosure

System overview

A complete research data-collection platform

The device guides a user through a breath test, manages sensor warm-up and acquisition, records five VOC sensor channels, and exports the resulting dataset for later analysis. It is intentionally presented as a research platform rather than a direct glucose-measurement device.

01 · ACQUIRE

Breath and sensor data

A controlled airflow path directs exhaled breath through a chamber containing five Figaro VOC sensors.

02 · PROCESS

Embedded control

An ESP32-based control system manages heaters, sensor sampling, the display, user input, and test sequencing.

03 · EXPORT

Digital research records

Test data can be transferred digitally for research logging, review, and comparison with externally collected glucose measurements.

System architecture

The system combines sensor heating and analog acquisition, an ESP32-based controller, a touchscreen interface, user input, audible feedback, rechargeable power, and digital research-data handling.

Hardware block diagram for the Breathalyze-BG platform — System-level hardware architecture used to guide electrical integration.

Electrical design

Custom multi-board embedded hardware

The electrical architecture was divided across a main four-layer PCB, a dedicated sensor board, a button board, and a display adapter. This modular approach simplified assembly, serviceability, and mechanical integration.

Main control PCB

ESP32 controller, battery interface, power conversion, sensor signal conditioning, buzzer driver, heater control, and system connectors.

VOC sensor board

Five Figaro sensors arranged inside the airflow chamber with dedicated load resistors and filtered analog outputs.

User interface boards

Display adapter and button PCB connect the touchscreen, controls, and internal wiring to the main electronics.

Four Breathalyze-BG circuit boards connected with ribbon cables as an integrated electronics assembly — **Integrated electronics assembly.** The main control board, sensor board, display adapter, and button board were linked through modular ribbon-cable connections before installation.

Populated-side render of the main Breathalyze-BG PCB — Main four-layer PCB, populated component side.

Populated-side render of the five-sensor daughter PCB — Five-sensor daughter board used inside the airflow chamber.

Populated-side render of the user-interface button PCB — User-interface button board.

Populated-side render of the display adapter PCB — Display adapter board for the touchscreen connection.

Front view of the assembled main, sensor, and button circuit boards — Assembled PCBs, component side.

Rear view of the assembled main, sensor, and button circuit boards — Rear assembly view showing ribbon interfaces and analog circuitry.

Embedded software

Guided test sequencing and data export

Firmware coordinates device startup, sensor warm-up, guided breath testing, acquisition, display updates, audible feedback, and digital data export.

Initialize

Configure the display, sensor channels, communication interfaces, and peripheral controls.

Warm up

Power the sensor heaters and guide the user through the approximately two-minute preparation period.

Acquire

Capture synchronized sensor readings during the guided breath test.

Export

Format the dataset for digital transfer and later research analysis.

Firmware documentation

The device firmware guide records configuration details and the operational sequence used for initialization, sensor warm-up, guided sampling, display updates, and data handling.

Open the firmware configuration guide

Final Prototype Demonstration

This demonstration highlights the completed Breathalyze-BG system, including the guided test workflow, device interface, sensor acquisition, and digital data export.

Mechanical & airflow design

Enclosure development guided by CAD and CFD

The enclosure was iteratively refined in Fusion 360 to accommodate the electronics, improve usability, and direct exhaled air through the sensor chamber. Autodesk CFD was used to visualize velocity and airflow distribution through the mouthpiece and chamber.

Exploded CAD view of the final enclosure and internal mounts — Exploded assembly showing the enclosure, sensor chamber, display mount, and internal structure.

Side-view Autodesk CFD streamline analysis through the angled mouthpiece and sensor chamber — Side-view CFD streamlines through the angled mouthpiece and sensing chamber.

Isometric Autodesk CFD streamline analysis within the sensor chamber — Isometric airflow visualization used to evaluate distribution and recirculation.

Velocity legend for the Autodesk CFD streamline simulations — Velocity scale associated with the CFD streamline figures.

CFD airflow animation, view 1.

CFD airflow animation, view 2.

Exploded enclosure assembly animation exported from the CAD model.

Final validation

Verified system-level outcomes

The archived material does not include every original bench plot, so this section presents only the final outcomes that were recorded for the completed prototype. No unsupported measurements are added.

Guided operation

The integrated display and button interface guided users through initialization, warm-up, breath sampling, and completion of a test sequence.

Sensor readiness

The five heated VOC sensors used an approximately two-minute warm-up period before the guided collection sequence.

Portable runtime

Battery testing supported an estimated runtime of approximately 50 tests per charge under the final operating workflow.

Final package

The completed handheld enclosure measured approximately 128 × 52 × 61 mm and integrated the electronics, battery, sensor chamber, display, and controls.

Digital data handling

The completed workflow supported digital transfer of collected research data for storage and later comparison with external measurements.

Prototype handoff

The completed prototypes and supporting project materials were handed off to the university research client at graduation.

Project gallery

From early prototypes to the completed device

Use this section for the strongest visual evidence of the design process. Six to twelve curated images are better than a large unfiltered dump.

Completed black Breathalyze-BG prototype shown from the front and side — Completed black prototype with touchscreen and mouthpiece.

Completed black Breathalyze-BG prototype powered on — Final device powered on during system integration.

Completed translucent Breathalyze-BG prototype viewed from the front — Translucent enclosure version showing the final user interface.

Side view of the translucent Breathalyze-BG enclosure — Side geometry and button placement.

Rear view of the translucent Breathalyze-BG enclosure and sensor ventilation — Rear airflow openings and sensor-chamber packaging.

Disassembled 3D printed enclosure components — 3D-printed enclosure components before final assembly.

Breathalyze-BG display showing a guided test interface — Guided test interface displayed on the integrated touchscreen.

Breathalyze-BG display showing a completed test result interface — Device interface during the final test workflow.

Connected electronics assembly laid out before enclosure installation — Modular electronics and ribbon-cable layout before installation.

Project contributors

Team and responsibilities

The project combined hardware, firmware, application, database, mechanical, and system-integration responsibilities across a three-person team.

Juan Ali Ruiz Guzman

Lead Hardware Engineer
System architecture, PCB design, power and sensor electronics, enclosure design, CFD analysis, prototype assembly, system integration, and validation.

Logan Cacy

Software & Mobile Application Engineer
Mobile application development, database integration, data handling, and research-data storage workflow.

Kyler Exley

Embedded Firmware Engineer
ESP32 firmware, user-interface behavior, sensor acquisition control, device logic, and QR-based data transfer.

Faculty advisor & client

Dr. Sudhir Shrestha · Department of Engineering Science / Intelligent Systems Laboratory, Sonoma State University

Industry advisors

Matteo Maurice · M-Force Engineering
Oliver Woelfel · Advanced Collision Repair Solutions

Breathalyze-BG team presenting the completed prototype at the Sonoma State University Senior Design Symposium — **Senior Design Symposium.** Kyler Exley, Logan Cacy, and Juan Ali Ruiz Guzman presenting the completed Breathalyze-BG prototype and project poster.

Breathalyze-BG team during prototype integration in the engineering laboratory — **Development and integration.** The team with prototype hardware during final system assembly and validation.

Acknowledgements

Breathalyze-BG was developed during the 2025–2026 Electrical Engineering Senior Design program at Sonoma State University. The team thanks Dr. Sudhir Shrestha, the Intelligent Systems Laboratory, M-Force Engineering, and Advanced Collision Repair Solutions for their guidance, mentorship, and support.

Documentation & design files

Available project resources

These files retain their original project filenames for traceability.

Mainboard PCB SchematicPDF Sensor Daughter Board SchematicPDF UI Button Board SchematicPDF Display Adapter Board SchematicPDF Firmware Instructions & Configuration GuideDOCX BLE InformationDOCX Backbone CAD ModelSTL Sensor Chamber CAD ModelSTL Sensor Mount CAD ModelSTL Display Mount CAD ModelSTL Button Mount CAD ModelSTL