LEGO Mounting & Enclosure System¶

A distinctive hallmark of the m-lego hardware philosophy is using LEGO building elements as precision structural enclosures. Rather than relying on custom 3D-printed plastic cases that warp, fracture, or need frequent reprints, the sensor boards are engineered to standard LEGO mechanical tolerances.

Grid Geometry & Hole Footprints¶

Standard LEGO bricks use an exact metric grid:

Stud Pitch: 8.0 mm center-to-center in both X and Y directions.
Stud Diameter: 4.8 mm nominal (4.80 mm – 4.85 mm).
Stud Height: 1.7 mm.
Plate Thickness: 3.2 mm (one-third the height of a standard brick).

   |<--- 8.0 mm --->|
   +----------------+
   |    (4.8 mm)    |
---+     [Stud]     +---

The `LegoHole_4875` Footprint¶

In KiCad, the mounting holes are defined with the custom footprint LegoHole_12x6u_4875.kicad_mod (and 8x6u variant): * Hole Diameter: 4.875 mm (plated or non-plated through-hole). * Clearance: The extra 0.075 mm diameter allows the PCB to slide smoothly onto LEGO studs without binding or scratching the plastic, while retaining tight friction to prevent lateral shifting.

Available 3D CAD Models (STEP)¶

The m-lego/sensor repository provides exact STEP models in the 3d/ directory for full 3D assembly verification:

Model File	Description
`ESP32-C3 supermini v5.step`	ESP32-C3 SuperMini MCU with USB-C connector
`WeAct-EpaperModule-2.13 Board 3D.step`	WeAct 2.13" E-Paper display module
`WeAct-EpaperModule-1.54 Board 3D.step`	WeAct 1.54" E-Paper display module
`Waveshare 1.54 E ink - Display Flat Mount.stp`	Flat display mount adapter
`Waveshare 1.54 E ink - Display Flush Folded.stp`	Flush folded display mount
`Waveshare 2.13 (D) E-ink - Reverse Mount.stp`	Reverse-mount display configuration
`GY-BME280.STEP` / `CJMCU-680.STEP`	Bosch climate breakout board geometry
`Gy -SGP30.step` / `GY-SGP40.step`	Sensirion air quality sensor modules
`TEMT6000 v2.step`	Ambient light sensor carrier
`hexagonal_spacer_MF_M2.5_H09_HEX5.step`	9 mm M2.5 nylon spacer for display elevation
`hexagonal_spacer_MF_M2.5_H11_HEX5.step`	11 mm M2.5 nylon spacer

Enclosure Construction Guide¶

+-------------------------------------------------------------+
|                     E-Paper Display                         |
+-------------------------------------------------------------+
  | (9mm Standoffs)                                        |
+-------------------------------------------------------------+
|                      Sensor PCB                             |
+-------------------------------------------------------------+
  | (4.875mm Stud Holes)                                   |
+=============================================================+
|             Baseplate: 12x6 or 8x6 LEGO Plate               |
+=============================================================+

1. Base Layer¶

Start with a genuine 12×6 LEGO plate (LEGO part 3028 / 4875) or an 8×6 plate for the mini board. Ensure the top surface is clean.

2. PCB Placement¶

Press the PCB directly onto the base studs. The corner holes align with the outer studs of the grid. If desired, standard 1×1 round tiles or bushings can be pressed over the studs above the PCB for a lock fit.

3. Display Standoffs¶

To prevent the e-paper ribbon cable from straining against the PCB components, install two 9 mm or 11 mm M2.5 nylon hexagonal spacers into the designated mounting holes. The e-paper display rests on these standoffs with double-sided tape or M2.5 screws.

4. Thermal Insulation Advantage¶

Unlike tightly sealed commercial plastic enclosures where the Wi-Fi MCU's heat warms the casing and inflates temperature readings by 2°C to 5°C, the LEGO open-stud framework maintains a natural convection boundary: * Ambient air flows freely underneath the carrier. * The temperature sensor is spaced 35 mm away from the ESP32 heat sink area. * Eliminates the need for aggressive software temperature offset compensations.