System
Integration

HigiBox is a compact sanitary pad dispenser that stores products vertically and releases one unit through a motor-driven spiral mechanism. The complete system needed to integrate mechanical structures, electronics, power systems, sensors, interfaces, and software into a single cohesive device.

HigiBox was inspired by commercial sanitary pad vending machines and Arduino-based dispensers. These references showed me how rotating spirals could move products forward and how empty space below the storage area could contain electronics.

Before detailed 3D modeling, I sketched how main systems could be arranged inside the enclosure:

The first proposed enclosure provided enough space while maintaining compact form:

• Width: 40 cm
• Height: 22 cm
• Depth: 13 cm

I began modeling the first version of the dispenser in Autodesk Inventor. This model was not intended to represent the final appearance of HigiBox. It was an initial draft that helped me understand the available internal space and check whether the storage area, dispensing spiral, motor, electronics, and product outlet could fit inside the proposed enclosure.

This draft allowed me to divide the product into functional areas. The spatial planning was crucial to ensure all systems could coexist:

To obtain a more realistic representation, I downloaded reference CAD models of the electronic components. These models were not designed by me; they were used only to estimate the size and space required by each component inside the assembly:

Component CAD references and assembly exploration:

After importing the component models into Inventor, I placed them inside the enclosure to identify possible collisions and evaluate different mounting positions:

I also created an exploded assembly to visualize the relationship between all major components and understand the assembly process:

However, this assembly was still a work-in-progress model. Its primary purpose was to guide the integration process and help identify the remaining design decisions that needed to be made:

By this stage, I had all principal electronic components and materials ready for testing. This allowed evaluation of dimensions, connections, power requirements, and compatibility before finalizing the design.

The rectangular enclosure would remain closed during normal operation, allowing the electronic system to be protected inside the dispenser. The internal layout divides the space into functional areas:

Component	Description	Source	Cost (USD)	Image
TFT LCD Display	2.8-inch touchscreen for cycle, battery, stock info	Zacatrex Electrónica	$28.57
TCA9548A Multiplexer	I2C bus multiplexer for dual sensors	Zacatrex Electrónica	$2.29
ULN2003 Motor Driver	Controls the 28BYJ-48 motor coils	Zacatrex Electrónica	$1.43
28BYJ-48 Stepper Motor	Rotates the dispensing mechanism	Fab Lab ULima	$2.86
LM2596 Converter	Step-down: 12V to 5V power regulation	Zacatrex Electrónica	$2.00
INA219 Power Sensor	Voltage, current, and power monitoring	Zacatrex Electrónica	$5.71
12V Rechargeable Battery	Powers the system with USB Type-C charging	Zacatrex Electrónica	$20.00
VL53L0X Sensors (×2)	Time-of-Flight distance sensors for stock & hand detection	Zacatrex Electrónica	$6.86
Jumper Cables	For prototyping and integration testing	Fab Lab ULima	$1.43
White Acrylic (4mm)	Enclosure and internal divisions material	Fab Lab ULima	$30.00
PolyLite White PLA	3D printing material for supports & parts	Fab Lab ULima	$20.00
PolyLite Black ABS	3D printing material for stronger components	Fab Lab ULima	$18.57
XIAO ESP32-C3	Main microcontroller with Wi-Fi & Bluetooth	MTLab UNI	$14.29
Custom PCB Material	Copper-clad PCB for milling & manufacturing	Fab Lab ULima	$2.28
TOTAL COST	USD 156.86

The following custom elements needed to be designed and manufactured specifically for HigiBox:

• Acrylic enclosure and internal divisions
• Custom PCB design and milling
• Rotating dispensing spiral
• Motor-to-spiral coupling mechanism
• Motor support structure
• Sensor holders and spacers
• PCB protective case
• Rounded enclosure corners
• Cable guides and internal mounts
• Control software and TFT interface

Distance sensing was essential because one sensor would monitor stock levels while another would detect the user's hand presence. I evaluated multiple sensor approaches before selecting the VL53L0X Time-of-Flight sensor.

Initially, I considered creating an infrared sensor using a separate emitter and receiver:

However, this solution required precise calibration and was affected by alignment and ambient light variations. I therefore selected the VL53L0X Time-of-Flight sensor, which uses an invisible infrared laser and communicates through I2C.

I first tested the sensor independently to understand its connections, measurement range, and response time before adding it to the complete system.

#include <Wire.h>
#include <Adafruit_VL53L0X.h>

Adafruit_VL53L0X lox = Adafruit_VL53L0X();
const int pinLed = 8;

void setup() {
  Serial.begin(115200);
  pinMode(pinLed, OUTPUT);
  digitalWrite(pinLed, LOW);
  
  while (!Serial) { delay(1); }
  Serial.println("Starting VL53L0X test...");
  
  if (!lox.begin()) {
    Serial.println("Error finding VL53L0X! Check connections.");
    while (1);
  }
  Serial.println("VL53L0X ready.");
}

void loop() {
  VL53L0X_RangingMeasurementData_t measure;
  lox.rangingTest(&measure, false);
  
  if (measure.RangeStatus != 4) {
    int distancia = measure.RangeMilliMeter;
    Serial.print("Distance: ");
    Serial.print(distancia);
    Serial.println(" mm");
    
    if (distancia < 100) {
      digitalWrite(pinLed, HIGH);
    } else {
      digitalWrite(pinLed, LOW);
    }
  } else {
    Serial.println("Out of range or object too far.");
    digitalWrite(pinLed, LOW);
  }
  delay(1000);
}

The TFT display was one of the most difficult components to integrate, revealing important lessons about pin management and system architecture.

Unlike the VL53L0X and INA219 sensors, the TFT display does not use I2C. It communicates through SPI and requires several dedicated control pins.

I reviewed the XIAO ESP32-C3 pinout documentation, modified the PCB design, and reserved D8 specifically for the TFT display SPI connection.

After testing individual modules separately, I combined them progressively. Each stage helped identify wiring, pin-assignment, programming, power, and communication problems before transferring to the custom PCB.

Initially, I considered the XIAO nRF52840 for its compact size, low power, and Bluetooth. However, HigiBox required internet access for Wi-Fi time synchronization through an NTP server. The XIAO nRF52840 lacks integrated Wi-Fi, so I switched to the XIAO ESP32-C3.

Two power diagram versions show the evolution of the system design:

if (objetoCerca && stockPermite && !objetoAntes && !motorGirando) {
  girarUnaVuelta();
}

The motor activates only when: hand detected, dispensing permitted, detection is new, and motor not already moving. The objetoAntes variable prevents repeated dispensing while the user keeps their hand in front of the sensor.

I manufactured three PCB versions during HigiBox development, each improving upon the previous design through iterative testing and refinement.

The first board was too long for the internal space and eventually broke during testing. It demonstrated that the PCB needed to be smaller, stronger, and better adapted to the enclosure.

The second version was smaller with thicker traces, smoother routing, greater clearance, and improved milling offset. However, D8 and D7 were occupied by a button and LED, creating conflicts with the TFT display. Some connectors were also too close to the board edge.

The third board corrected all pin conflicts and became the final PCB. It included:

• Eight 3.3V outputs
• Ten GND outputs
• Six 5V outputs
• Two D6 connections
• Two D7 connections
• D8 reserved for TFT SPI

These extensions allowed modules to connect directly to the custom PCB, eliminating external breadboards and reducing loose wiring.

After completing the final PCB, I designed a 3D-printed support to protect its edges and provide internal mounting points.

The PCB case included a 0.40mm FDM tolerance offset, 7mm external support offset, 1mm base, and 3mm outer ring to protect connectors and provide stable mounting inside the enclosure.

The integrated HigiBox system combines mechanical, electrical, and software components into a cohesive smart dispensing device. All systems work in concert through the central XIAO ESP32-C3 microcontroller.