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Archive for December 28th, 2018

Astable Multivibrator: RGB LED and Radome Spider

Well, a spider with half the proper leg count:

RGB LED - radome test

RGB LED – radome test

One could argue the LED spider has an unusually large abdomen, but I’m not going there.

The solid model looks the same way:

Astable Multivibrator Battery Holder - RGB LED Spider - radome

Astable Multivibrator Battery Holder – RGB LED Spider – radome

And, yes, those are eye protection caps over the four wire struts, most useful during construction while maneuvering the radome into position.

For reasons unknown to me, they’re called “Pirhana” LEDs:

RGB LED - wiring

RGB LED – wiring

I trimmed off half of each pin, soldered on 28 AWG color-coded silicone wires, threaded wires through openings, then rammed the LED package into the recess so it sits just below the radome’s curve. The dent matching the ball comes from the chord equation, as always, and looks pretty good.

The radome is, of course, a one-star ping pong ball from the usual big box retailer’s sporting goods section. The stamped logo sits at a random position with respect to the ball’s interior structure (visible when lit, as in the top picture), so I erased it with a fine-grit sanding sponge. Hollow plastic golf balls might work just as well, with an even more interesting surface texture.

The source code includes a cutaway look at the printed parts to verify their innards:

Astable Multivibrator Battery Holder - RGB LED Spider - fit view

Astable Multivibrator Battery Holder – RGB LED Spider – fit view

The OpenSCAD source code as a GitHub Gist:

The original doodles give useful dimensions, plus some details not withstanding the test of time:

RGB LED Radome Spider - doodles

RGB LED Radome Spider – doodles

The actual center-to-center distances for the wire posts come from the battery dimensions, rounded up or down as appropriate, to the nearest multiple of 5 mm, so those are just serving suggestions.

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