mechanicals: add OpenSCAD enclosure + STL exports (base + lid)

Author: Mummanajagadeesh

mechanicals/README.md

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+# SPDX-FileCopyrightText: 2026 Mummana Jagadeesh
+# SPDX-License-Identifier: Apache-2.0
+
+# Mechanicals - FIR Accelerator Breakout Enclosure
+
+Simple two-part enclosure for the FIR Accelerator breakout board.
+Designed for FDM 3D printing in PLA or PETG.
+
+## Parts
+
+- `enclosure.scad` — OpenSCAD source (parametric)
+- `enclosure_base.stl` — Bottom shell with PCB mounting posts
+- `enclosure_lid.stl` — Top cover with label and ventilation slots
+
+## PCB Dimensions
+
+- 60mm x 40mm x 1.6mm
+- M2.2 self-tapping screws for PCB mounting (3.5mm from corners)
+
+## Cutouts
+
+- Left side: GPIO[8] input connector slot
+- Right side: GPIO[9] output connector slot
+- Front: UART debug header
+- Back: Power connector
+
+## Print Settings
+
+- Layer height: 0.2mm
+- Infill: 20%
+- Supports: Not required
+- Material: PLA or PETG

mechanicals/enclosure.scad

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+// SPDX-FileCopyrightText: 2026 Mummana Jagadeesh
+// SPDX-License-Identifier: Apache-2.0
+//
+// FIR Accelerator Breakout Board Enclosure
+// PCB dimensions: 60mm x 40mm
+// Designed for FDM 3D printing (PLA/PETG)
+
+// Parameters
+pcb_x = 60;
+pcb_y = 40;
+pcb_z = 1.6;
+wall  = 2.0;
+floor = 2.0;
+lid_h = 3.0;
+inner_h = 15.0;  // tall enough for connectors/headers
+post_r = 2.0;
+post_h = 3.0;
+screw_r = 1.1;   // M2.2 self-tap
+
+// Mounting hole positions (3mm from corners)
+mh_offset = 3.5;
+mh_pos = [
+    [mh_offset,       mh_offset      ],
+    [pcb_x-mh_offset, mh_offset      ],
+    [mh_offset,       pcb_y-mh_offset],
+    [pcb_x-mh_offset, pcb_y-mh_offset]
+];
+
+module mounting_post(h) {
+    difference() {
+        cylinder(r=post_r, h=h, $fn=20);
+        cylinder(r=screw_r, h=h+1, $fn=16);
+    }
+}
+
+module base() {
+    difference() {
+        // Outer shell
+        cube([pcb_x + 2*wall, pcb_y + 2*wall, floor + inner_h]);
+        // Inner cavity
+        translate([wall, wall, floor])
+            cube([pcb_x, pcb_y, inner_h + 1]);
+        // GPIO[8] input slot - left side
+        translate([0, pcb_y*0.4 + wall - 3, floor + 2])
+            cube([wall + 1, 6, 8]);
+        // GPIO[9] output slot - right side
+        translate([pcb_x + wall - 0.5, pcb_y*0.6 + wall - 3, floor + 2])
+            cube([wall + 1, 6, 8]);
+        // UART header cutout - front
+        translate([pcb_x*0.4 + wall - 5, 0, floor + 4])
+            cube([10, wall + 1, 8]);
+        // Power connector cutout - back
+        translate([pcb_x*0.4 + wall - 4, pcb_y + wall - 0.5, floor + 4])
+            cube([8, wall + 1, 8]);
+    }
+    // Mounting posts
+    for (p = mh_pos) {
+        translate([p[0] + wall, p[1] + wall, floor])
+            mounting_post(post_h);
+    }
+}
+
+module lid() {
+    difference() {
+        cube([pcb_x + 2*wall, pcb_y + 2*wall, lid_h]);
+        // Label recess
+        translate([wall + 5, wall + 5, lid_h - 0.8])
+            linear_extrude(1)
+                text("FIR SoC", size=5, font="Liberation Sans:style=Bold");
+        // Ventilation slots
+        for (i = [0:3]) {
+            translate([wall + 8 + i*12, wall + pcb_y/2 - 5, -0.1])
+                cube([6, 10, lid_h + 0.2]);
+        }
+    }
+}
+
+// Render base by default
+// Use: openscad -D 'part="lid"' to render lid
+part = "base"; // override with -D 'part="lid"'
+
+if (part == "base") {
+    base();
+} else if (part == "lid") {
+    lid();
+} else {
+    // Show both for preview
+    base();
+    translate([0, pcb_y + 2*wall + 5, 0])
+        lid();
+}