LED rings - the missing post

More than three years ago I did a lot of prototyping of LED dials/rings that I will use to indicate the position of the endless potentiometers on my synth.

I can however only find a couple of posts here about it, one is from the early prototyping of a diffuser lense, and the other one from when I sent the PCB to production - but then it ends.

I did however take some photos and videos of everything, so as I just picked up the idea again I thought it would be nice to post about it.

A diffuser test with a single normal led. The diffuser consists of two layers, one with an engraved circle that diffuses the light, and one where the center has been cut out and a slit has been made for each cell, to prevent light from bleeding between cells. It worked impressingly well for a first try.

 

 

The LED ring PCB, 31 + 1 LEDs in a 270 degree arc (to match a normal potentiometer)

Diffuser prototype. Here I've engraved a ring, and then cut slits in an attempt to keep light leakage between elements to a minimum

A similar version, but here the engraving is on a separate piece of acrylic so we have two layers.

Not entirely sure about this one, but I think I've engraved both slits and ring, but engraved the slits deeper.

Same as above but with the additional second layer.

Not sure what combination this is but it's starting to look good

My text for this says "cut 3mm outside". I did some versions where i had an additional cut outside or inside to prevent even more light bleeding

I even did a version where I put tiny black paper dividers between each cell. It worked fairly well but was extremely impractical and would take ages for the number of pots I need.

I tried cutting a mask in multiple layers of thick paper to prevent light bleeding under the acrylic.

After all these white diffuser trials, I decided to try out red acrylic instead. That worked wonders!

I actually really like this look. The dots are clearly visible but still cool. And the background gets rather dark as the PCB is green, so I actually think it looks better when turned off than the next version. It is also the simplest to produce.

This is also a really good version. I think it is a combination of the best cell-and-engraving version with the red lense, possibly with black cutouts

Here are some videos of the ring in action:

All in all, I was rather satisfied with the result, so I decided to move on to other things.

Then, today, a colleague sent me a link to this video:

https://www.youtube.com/watch?v=tHL4RYGSvg4

Finally, someone has made a good enough commercial version of a led ring:

 

It is prohibitively expensive though, around $10 per ring! 

https://www.aliexpress.com/item/1005005361069637.html

But this got me thinking - how do they actually make those rings? Why does it not bleed between cells, and more importantly - how can I do something similar?

So now I'm back to the idea of cutting a mask again. The Bargraph ring is 3.4mm high, so I will try cutting a 3mm high mask out of black MDF or even acrylic. I am not sure how detailed I can get it so i will try some various versions - from 0.3 to 0.7mm walls between cells, and both engraving and cutting - engraving takes much longer but also uses lower temperatures so it may be possible to get a thinner wall.

Mask for cutting/engraving 3mm thick material

 

I then have a few options. I can try adding a diffuser on top, and then a red layer on top of that, that would probably look quite nice. 

 Or, I could try placing the mask over the leds and fill the holes with resin, and then sand the top to get either a smooth or diffuse finish. Using a clear resin would give me lightpipes up to the surface, possibly with some internal reflection to even out the light. I could also try translucent resin, or even red resin.

I think this has some chance of looking good, and it would also be fun to try out. I will start out with the laser cutting and see how it works out.