Sensor fusion module

Compact Multi-Sensor Fusion Module for Confined-Space Inspection

A miniaturized multi-sensor module that combines distance, motion, vibration, and light sensing into a single environment-awareness output — designed and documented like a real inspection-robot sensor module: schematic-first, bus-based, with a routed PCB layout.

This project focuses on the hardware design side of sensor integration for mobile/inspection robotics: schematic capture, PCB layout with a genuine I2C bus device, and design-rule validation using KiCad.

Overview

The module integrates four sensing modalities on a single board built around an ESP32-WROOM-32:

• Distance — HC-SR04 ultrasonic sensor
• Motion — HC-SR501 PIR sensor
• Orientation/Vibration — ADXL343 accelerometer (I2C)
• Light — LDR voltage divider

The ADXL343 was chosen specifically as a genuine I2C bus device, so the design demonstrates real bus-based sensor integration (SDA/SCL) rather than only GPIO-polled sensors.

Hardware

All components are from existing hardware stock — no new purchases were made for this project.

Schematic

Power distribution (+3.3V/GND via PWR_FLAG), HC-SR04 (TRIG=IO13, ECHO=IO12), PIR (OUT=IO27), ADXL343 in I2C mode (SDA=IO21, SCL=IO22, CS tied to +3.3V, SDO/ADDR tied to GND), and the LDR divider feeding IO34.

Electrical Rules Check (ERC) passed cleanly; the only remaining warnings are expected "unused pin" notices on unconnected ESP32 GPIOs, which is normal and intentional for this design.

PCB Layout

Key layout notes:

• The ESP32-WROOM-32's antenna keepout zone (top of board) is kept clear of copper, respecting the module manufacturer's RF layout guidance even though this design does not undergo RF certification.
• Routing was completed using KiCad's FreeRouting auto-router plugin after manual routing became impractical for the trace density on a single/two-layer board of this size.

3D Render

Design Decisions & Constraints

This project is scoped as a documentation/design exercise, not a fabrication-ready board. As such, three DRC items were reviewed:

1. Antenna keepout violation on U1 — the ESP32-WROOM-32 footprint includes a built-in antenna keepout rule; this design does not require RF certification, so the rule is not applicable, and the antenna area is visually confirmed clear of copper.
2. Edge.Cuts outline continuity warning — a minor board-outline rule warning that does not affect the schematic-to-layout correspondence or component placement shown here.
3. Two short (~5mm) unconnected GND stub traces near the ESP32 footprint. In a fabrication-intended revision, these would be routed to closure before manufacture; for this documentation-scope design they do not affect the design intent being demonstrated.

Repository Structure

• images/ — README figures
• sensor-fusion-module.kicad_sch — Schematic
• sensor-fusion-module.kicad_pcb — PCB layout
• sensor-fusion-module.kicad_pro — KiCad project file
• sensor-fusion-module.pdf — Schematic export (PDF)
• sensor-fusion-module-F_Cu.pdf — PCB layer export (PDF)

Tools Used

• KiCad 10 (schematic capture, PCB layout, 3D viewer)
• FreeRouting (auto-routing plugin)