ElektroCasterV2: Making a new light emitting fretboard

I’m making a new version of the ElektroCaster and want to share some insights into the process. This post is about the new LEF (light emitting fretboard).

The old approach

The WS2812b RGB-LEDs are a real treasure when you need to control large amounts of LEDs individually without the need of complex (and big) circuits. On my last attempt I cut a commonly available WS2812b-stripe into pieces an fitted them into a 3d-printed fretboard template and then soldered them back together

The new approach

This time I created a pcb were I solder the LEDs on to. This reduces the effort of replication and also makes it far more robust, easy to troubleshoot and to repair. The challenge here is to make a dynamic circuit: The LEDs have to be perfectly aligned to the frets and the strings of the fretboard. That means that the pcb traces also have to change according to the position leds. On top of that, I wanted a parametric design which allows me to change the scale and the dimensions of the fretboard afterwards. That’s a perfect task for “The Programmers Solid 3D CAD Modeller” OpenScad, a program language for 3d-modelling. Here are the steps i’ve taken so far:

1) Find a layout

I started writing the code in OpenScad to make footprints of the leds and then arrange them into a “fret-string-grid”. Then I drawed in the traces by hand to figure out the most simple and compact way to lay out the traces without intersecting each other. This seems to work best when every second row (fret) is rotated 180°. The dots mark the holes where the power traces are connected (red to red rows and black to black rows).

2) Generate the traces

The most difficult and time consuming part was to make a dynamic model of the traces in OpenScad. I wanted it to be as flexible as possible, enabling me to fine tune parameters like the position of the LEDs relative to the frets, number of frets, scale, width and angle. Since the final pcb is almost 50cm long, I had to cut it into two pieces and put them side by side.

3) Engrave, drill, cut

I use Flatcam (to generate) and bCNC to send the gcode to the mill. Both programs give me a good open source alternative to popular closed platforms. Making pcbs with my mill is always a thrill. You have to be very concentrated, every little mistake can ruin your tool (and your day).
I’m happy with the results although they don’t look very nice. I had to sand them quite a bit to smooth the edges of the traces and get rid of small bits of copper which can lead to short circuits. The bad finish is because of a dull tool – I have to learn how to sharpen them cause they do not last very long and are quite expensive.

4) Solder the LEDs

Next

The next steps roughly are:

  • Make the actual fretboard (a 3d-printed overlay were the frets are mounted on and the LEDs can shine through)
  • Create the back of the neck (were hand and thumb rest)

The way and the tightness of how those parts interconnect is crusial for a good feeling and consistency. That’s something I’ve spent much thought on. But more on this in my next post…

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