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Updated: 2.10.26
A DFM/DFA Approach to Spatial Input
The Galaxy-Rat is a solid-state, six-degree-of-freedom (6-DOF) spatial interface designed with a unique emphasis on Design for Manufacturability (DFM) and Assembly (DFA). By utilizing spatial magnetic field reconstruction rather than traditional optical sensing, the device achieves high-precision input while significantly reducing mechanical complexity.
Side Comment: I've been using Space Mouse for over a decade. They are a phenomenal product! I hope the amazing team at 3D Connection finds imitation to be the greatest form of flattery; and that this device was inspired by their product as an educational tool to teach the principles of manufacturability.
Key Technical Features:
Sensing Architecture: Employs a multiplexed 3×3 array of MLX90393 triaxial magnetometers to resolve translational (X, Y, Z) and rotational (Rx, Ry, Rz) vectors.
Integrated Processing: Powered by an RP2040 microcontroller that performs real-time analysis and filtering to output calibrated motion data.
Hardware Efficiency: Features a consolidated single-motherboard design that eliminates internal wiring overhead and minimizes assembly variability, making it ideal for repeatable production.
Flexibility: The simplicity of the electronics allows for flexible integration into a variety of potential classroom learning labs.
CAD Integration: Native SolidWorks API integration provides, low-latency viewport control rather than mouse emulation.
Core Objective: To provide a scalable, manufacturable, and high-fidelity spatial input platform that demonstrates the intersection of magnetic field theory and efficient embedded systems design.
Custom PCB
This project served as a return to PCB design (something i had not actively done in about a decade). My background is in mechanical engineering but i have always had a passion for Electrical.
The design consolidates the RP2040 microcontroller, a multiplexed 3×3 triaxial magnetometer array, and all power and USB interfaces into a single board to reduce the risk of assembly error by simplifying manufacturing.
The layout is optimized for production feasibility:
Integration: All necessary components are merged into one unit to mitigate any internal wiring when integrated into a complete product.
Assembly: A top-side SMD configuration facilitates efficient hot-plate assembly, making the board accessible for student-led production with minimal hand-soldering required.
Precision: Symmetrical sensor placement ensures consistent data acquisition.
Scalability: While the board is designed to be feature-rich (supporting eight individually addressable LEDs and up to nine sensors) it allows for modular population to meet specific cost or complexity targets. For simplified applications, the unit remains fully functional when populated with as few as one magnetometer and the core logic components, providing a versatile platform for both high-fidelity sensing and low-cost implementation.
Note: Shown on-Board is a RP2040-NANO (no USB) which shares the same footprint and hardware as the RP2040-ZERO that is actually used.
The schematic integrates:
Nine MLX90393 triaxial magnetometers (multiplexed)
Decoupled 3.3V and 5V power distribution
USB interface to the RP2040
Filtering and signal conditioning components
Hardware (Mouser and Amazon)
1. Triaxial Magnetometer (Qty: 9)
MLX90393ELW-ABA-011-RE
Mouser #: 482-90393ELWABA011RE
https://www.mouser.com/ProductDetail/Melexis/MLX90393ELW-ABA-011-RE
2. 4-to-16 Decoder (Qty: 1)
CD74HC154M96G4
Mouser #: 595-CD74HC154M96G4
https://www.mouser.com/ProductDetail/Texas-Instruments/CD74HC154M96G4
3. Level Shifter / Buffer (Qty: 2)
SN74AHCT1G126DBVR
Mouser #: 595-SN74AHCT1G126DBVR
https://www.mouser.com/ProductDetail/Texas-Instruments/SN74AHCT1G126DBVR
4. APA102-2020 Smart RGB LED (Qty: 8)
Adafruit DotStar Micro LED – 10 Pack
Mouser #: 485-3341
https://www.mouser.com/ProductDetail/Adafruit/3341
(One pack covers one board.)
5. 100 µF Bulk Capacitor (Qty: 2)
Panasonic EEE-FN1C101UR (16V, 100µF, SMD)
Mouser #: 667-EEE-FN1C101UR
https://www.mouser.com/ProductDetail/Panasonic/EEE-FN1C101UR
6. 100 nF 0603 Decoupling (Qty: 9)
Yageo CC0603KRX7R9BB104
Mouser #: 603-CC603KRX7R9BB104
https://www.mouser.com/ProductDetail/YAGEO/CC0603KRX7R9BB104
7. 100 nF 0402 (Qty: 1)
Samsung CL05B104KB54PNC
Mouser #: 187-CL05B104KB54PNC
https://www.mouser.com/ProductDetail/Samsung-Electro-Mechanics/CL05B104KB54PNC
8. 100 Ω 0603 (Qty: 5)
Yageo RC0603FR-07100RL
Mouser #: 603-RC0603FR-07100RL
https://www.mouser.com/ProductDetail/YAGEO/RC0603FR-07100RL
9. 100 kΩ 0402 (Qty: 4)
Yageo RC0402FR-07100KL
Mouser #: 603-RC0402FR-07100KL
https://www.mouser.com/ProductDetail/YAGEO/RC0402FR-07100KL
HID Firmware
The firmware presents the device to the host computer as a native USB HID and integrates with the solidworks API for viewport manipulation.
The RP2040 continuously:
Polls the multiplexed MLX90393 array
Reconstructs the 3D magnetic field state
Resolves that state into translational (X, Y, Z) and rotational (Rx, Ry, Rz) components
Filters and normalizes the motion vectors
Packages reports at a fixed update rate
SOLIDWORKS INTEGRATION
Currently, a "middleware" utility translates the HID output from the Galaxy-Rat and interfaces with the SolidWorks API: a native SolidWorks Add-in is currently under development to provide a seamless, integrated user experience.
The add-in maps six-axis motion directly to the active viewport camera transform using:
Rotation matrices
Translation vectors
Zoom scaling functions
Rather than emulating mouse movement, the add-in applies explicit API-level transformations. This ensures:
Predictable behavior
Low latency
Deterministic camera control
Future Work & Variations
The Galaxy-Rat Mainboard REV A was intentionally over-populated with hardware as the pilot mainboard was purchased in bulk.
As this is a prototype platform, the design was to deliberately deploy an over-expanded sensor array to allow software-defined optimization of sensor count, placement, and reconstruction algorithms. This approach enables empirical validation before committing to a reduced hardware configuration in a future revision. Likely fully integrating all components into a top-only component layout with native USB rather than a dedicated USB RP2040 ZERO dev board.
Modifiers:
Magnetometer reduction: Preliminary analysis suggests that full and reliable functionality may be achievable with as few as three triaxial magnetometers. Accordingly, the current board does not require full population of all SMD footprints.
LED Reduction: If a student-designed enclosure does not permit LED visibility, those components—along with the level shifters and bulk capacitor—may be left unpopulated to reduce cost without requiring additional board variants.
GPIO expansion: Though not explicitly used on the current concept, multiple Pins from the RP-2040 were intentionally made accessable with thru-hole pads for future use and expansion / customization of the end-product (i.e. Pushbuttons)
The Bottom Line
The Galaxy-Rat is a fully solid-state, manufacturable 6-DOF spatial input device designed around simplicity.
It implements 6-DOF sensing with spatial magnetic field reconstruction, consolidating all electronics into a single motherboard, and integrates natively with CAD software through standard API calls.
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