Version: ACS CC

VERIT-SCAN

A multi-sensor fresh fruit quality analyzer with data fusion from 4 physical domains

Author: Costache David
GitHub Project Link: Github

Description

VERIT-SCAN is a non-destructive fresh fruit quality analyzer that fuses measurements from four independent physical domains — aroma (VOC + humidity), firmness (elastic deformation under controlled force), apparent density (mass / laser-estimated volume), and electrical conductivity — into a single Overall Quality Score. The results are displayed locally on an OLED screen with RGB LED feedback and streamed via UART to a host PC for logging and plotting.

Motivation

Fruit quality assessment is traditionally subjective: we squeeze, sniff, and judge by appearance. These signals are real but hard to quantify, compare across samples, or log over time. VERIT-SCAN replaces subjective judgment with four quantifiable measurements drawn from distinct physical domains — chemistry (VOCs), mechanics (elasticity), geometry + mass (density), and electrochemistry (ionic conductivity). The project is an exercise in multi-sensor data fusion: no single sensor tells the whole story, but together they build a meaningful quality score. It also explores a non-destructive approach to firmness testing, replacing the traditional penetrometer (which damages the sample) with an elastic-deformation measurement that leaves the fruit intact.

Architecture

The system is structured around an async embedded runtime (Embassy on STM32U545) with the following architectural components:

Sensor Acquisition Layer — four concurrent async tasks, one per measurement channel:
- Aroma Task — reads BME680 over I²C every 500 ms (VOC resistance + humidity)
- Firmness Task — orchestrates the VL53L0X + HX711 interaction (baseline distance → force ramp → final distance)
- Density Task — combines HX711 weight reading with VL53L0X height estimation
- Conductivity Task — samples the internal ADC (14-bit) on the electrode divider
Fusion & Scoring Layer — a coordinator task that collects readings from the four acquisition tasks via Embassy channels, normalizes each raw value to a 0–100 score based on calibrated per-fruit-type thresholds, and computes the weighted Overall Quality Score.
Presentation Layer — three parallel output tasks:
- Display Task — renders scores on the SSD1306 OLED using embedded-graphics
- Indicator Task — drives the RGB LED via PWM (green/yellow/red mapping) and the buzzer at measurement completion
- Telemetry Task — streams a JSON line per measurement on UART2 (exposed as ST-Link Virtual COM Port) to the host PC
Host-side Plotting — a Python script (pyserial + matplotlib) running on the PC parses the JSON stream and plots all four scores + the overall score in real time.

Data flow: Sensors → Acquisition Tasks → (Embassy Channel) → Fusion Task → (Embassy Channel) → Display / Indicator / Telemetry Tasks.

(Graphical block diagram to be added.)

Architecture Diagram

Log

Week 5 - 11 May

I have assembled the hardware components on a breadboard and started prototyping the software architecture. Unfortunattely, the sensors weren't soldered properly, which caused a delay and force me to redo the wiring.

Week 12 - 18 May

I have securely mounted the hardware components onto their dedicated support structure, ensuring a clean, organized, and nice layout. The setup now features proper cable management and perfectly aligned sensors, giving the physical prototype a polished, final look. With the hardware architecture completely stabilized and visually refined, my focus has now shifted to the software development phase. I am currently writing and testing the firmware.

Week 19 - 25 May

Hardware

The core of VERIT-SCAN is a NUCLEO-U545RE-Q board, built around the STM32U545RE (ARM Cortex-M33, 160 MHz, 512 KB flash, 272 KB SRAM) with an integrated ST-Link V3 debugger. The board exposes four I²C buses, two UARTs, a 12-bit ADC, and a 14-bit ADC — the latter is used for the DIY conductivity channel, where two stainless-steel electrodes in contact with the fruit flesh form a voltage divider with a 10 kΩ precision reference resistor.

Three digital sensors share a single I²C bus: BME680 (VOC + humidity + temperature + pressure), VL53L0X (time-of-flight laser distance, used both for firmness-via-deformation and for height/volume estimation), and an SSD1306 0.96" OLED for local display. An HX711 24-bit ADC interfaces the 1 kg load cell, which is used both for weighing and for monitoring the controlled force applied during the non-destructive firmness test. User feedback comes from a common-cathode RGB LED driven by three PWM channels and a passive buzzer driven by a timer PWM. Communication with the host PC uses USART2, exposed transparently as a Virtual COM Port through the on-board ST-Link, so no external USB-to-UART adapter is needed.

Schematics

Schematic Diagram

Bill of Materials

Device	Usage	Price
NUCLEO-U545RE-Q	Main MCU board (STM32U545RE, Cortex-M33 @ 160 MHz, ST-Link V3 onboard)	already owned
BME680 I²C Module	Aroma measurement (VOC + humidity + temperature + pressure)	82.62 RON
VL53L0X ToF Module	Laser distance sensor — baseline + deformation measurement, height/volume estimation	17.04 RON
Load Cell 1 kg	Weight + controlled-force measurement during firmness test	12.80 RON
HX711 24-bit ADC	Load cell amplifier and ADC	4.57 RON
SSD1306 OLED 0.96" I²C	Local display of per-channel and overall scores	16.96 RON
RGB LED 5 mm common cathode	Quality indicator (green / yellow / red via PWM)	1.51 RON × 3
Passive buzzer 5 V	Audible signal at measurement completion	1.45 RON
2× Stainless steel screws M3/M4	DIY conductivity electrodes	~2 RON
Resistor 10 kΩ 1% metal film	Voltage divider reference for conductivity ADC channel	3.20 RON / 20 pcs
Resistor 220 Ω 1% metal film	Current limiting for RGB LED	3.20 RON / 20 pcs
Breadboard 400 points	Prototyping	6.62 RON × 2
Dupont wires 30 cm M-M and M-F	Interconnects	~16 RON

Software

Library	Description	Usage
embassy-stm32	Async HAL for STM32 (feature `stm32u545re`)	Core hardware abstraction: GPIO, I²C, ADC, UART, PWM, async timers
embassy-executor	Async task executor for `no_std` environments	Concurrent sensor acquisition and output tasks
embassy-time	Async time primitives	Timing for sampling periods and force ramps
embassy-sync	Sync primitives (channels, mutexes)	Inter-task communication between acquisition and fusion layers
ssd1306	Driver for SSD1306 OLED displays	OLED rendering over I²C
embedded-graphics	2D graphics primitives	Drawing score bars, text, and icons on the OLED
bme680	BME680 sensor driver	Reading VOC resistance + humidity
vl53l0x	VL53L0X ToF sensor driver	Distance / deformation / height measurement
loadcell	HX711 driver for load cells	Reading force and weight from the 1 kg load cell
defmt + defmt-rtt	Efficient logging framework	Debug output over RTT during development
probe-rs	Embedded flashing and debugging	Flashing firmware to NUCLEO-U545RE-Q via ST-Link V3
heapless	Fixed-capacity collections for `no_std`	Score buffers and telemetry line buffering
serde + serde-json-core	`no_std` JSON serialization	Formatting telemetry lines sent over UART
pyserial + matplotlib (host-side Python)	Host-side serial reader and live plotter	Parsing JSON telemetry from UART and plotting the 4 scores + overall in real time

Description​

Motivation​

Architecture​

Architecture Diagram​

Log​

Week 5 - 11 May​

Week 12 - 18 May​

Week 19 - 25 May​

Hardware​

Schematics​

Bill of Materials​

Software​

Links​