PCB Friday: LED Strip Helper Board Slides Into Aluminum Extrusion

Aluminum extrusion is commonly used as a building block for a wide range of maker and industrial products. Older-style Ender 3D printers, for example, were put together with this material. Extrusion is also used extensively in industry, often as an element of safety guarding, and sometimes to hold other equipment — like end-of-arm robot tooling.

The de facto extrusion standard in the maker world is known as "2020," e.g. 20mm x 20mm with a European-standard profile. A drawing for this type of extrusion is shown below, which can be ordered in different lengths and cut to size as needed.

[The PCB bit is coming soon — stay tuned!]

However, don't be confused if you hear extrusion called "80/20." This is actually a brand name for this type of extrusion, referencing the Pareto Principle, not actual profile dimensions. 80/20 is primarily an industrial brand, and wouldn't necessarily be compatible with what's discussed here — though the overall idea is certainly applicable.

2020 extrusion with PCB-compatible dimensions?

Considering the extrusion dimensions shown above, you can work out that the horizontal shelves indicated by the red arrows are each approximately 1.64mm long (4.3mm - (11mm - 5.68mm) / 2). If this sounds familiar, standard PCBs just so happen to be 1.6mm in thickness; therefore, this sort of extrusion is the perfect size to hold a small circuit board.

The width of the captured board should be approximately 10.5mm to slip into the extrusion without issue, and the geometry leaves 6.2mm of free width to work with on the top. There's slightly more width on the bottom, but you have to consider the vertical constraints.

That doesn't give you a ton of space, but it's enough to fit a 5050 addressable LED or a VQFN ATtiny1616 (see pg. 580) on either side. You do, however, have theoretically unlimited length for your PCB.

The idea

This idea came to me when working on a rather involved guitar pedal setup involving aluminum extrusion (see video below). A small length of non-addressable LED strip fits nicely inside of a 2020 profile, but holding it in place and soldering to it would be difficult.

After some thought and iteration, I came up with a helper PCB to help with soldering and lock the end of the LED strip into my 2020 extrusion. The user solders the non-addressable LED strip to (left) pads 1 and 2, while wires or male headers can be attached to (right) pads 1 and 2:

The PCB is designed in three thickness levels. The left (8mm) section slides freely in the extrusion section, allowing the LED strip to be soldered on, and heat shrink to be applied. The middle (10.5mm) section slides securely into the extrusion, keeping the contacts in the middle clear.

The right (14.5mm) section keeps the PCB hanging on the outside of the aluminum extrusion, which is locked in by the rest of my assembly. Some applications might want to forgo the 14.5mm tabs, so rat bites are provided for easy removal as needed.

The results

As shown in the short YouTube clip below at the ~9:30 mark, this device makes the job of soldering onto an LED strip much easier. It also mechanically locks everything into the aluminum extrusion.

I also made a similar board that's compatible with LED strips, and used it to help me hook up the lighting on my Hackstercaster guitar build. I haven't tested this version in actual extrusion, but as a soldering/attachment helper it works really well.

What about short circuits?

I designed my original PCB so that no wires or pads touch the extrusion, and the anodized surface of typical aluminum extrusion isn't conductive (as long as it isn't scratched). While I would be more nervous if I were dealing with high voltages and/or currents, I think this design is sufficiently safe for 9V as used here.

PCB and soldering technique ready for experimentation!

I'm just getting started with this technique, but I could see it used in all kinds of ways. Need a rigid structure for your lighting fixture? Extrusion to the rescue! Want to embed a little microcontroller in your extrusion-based 3D-printer structure? Why not?

Or, if you simply want an easy way to solder on LED strips, this little board has you covered! KiCad design files are available here. Hopefully Hackster readers can take this idea and run with it. Maybe that's you!

One final note: If you're wondering about this incredible dimensional coincidence, consider that if you convert a 1.6mm PCB into inches, you get .063in. The 1.64mm extrusion "shelf" converts to .065in. And 1/16th of an inch converts to a shockingly similar .0625in. While I don't know the entire history, I'd have to guess this numerical alignment... isn't a coincidence at all! -JC

Thanks for reading!

Thanks for reading my biweekly PCB Friday column! I'm looking forward to sharing more PCB-related knowledge and insights here, and I hope you'll follow along for the journey. You can find the pedal seen above and other musical hacks on the Cooked Audio YouTube channel, read my semi-technical musings at TechAdjacent.io, or email me: hi@jeremyscook.com!

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