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.

Finally a china version of the Alpha endless pots!

Hah! Finally! I just discovered these:

https://www.globalsources.com/Rotary-potentiometer/Rotary-potentiometers-1148135774p.htm

https://www.globalsources.com/Rotary-potentiometer/Rotary-potentiometers-1148135774p.htm

It's a clone of the Alpha RV112FF-series endless pots, this one is by HongYu and named H111KGP+T4 360°Endless:

http://www.hongh.com/product/291.html

NB: HongYu also sells a non-360°Endless version named H111KGP+T4, so be sure to order the correct one!

Here is the original RV112FF datasheet:

Compared to the one for the H111KGP+T4:

I'd say it's a drop-in replacement.

The specs are almost the same too, it's like they just copied the datasheet ;-)

RV112FF

H111KGP+T4 360°Endless

The MOQ at globalsources is 1000, but for a price of around $0.5-0.8 I get 1000 for the price of around 200 of the Alpha one. Now, I've already ordered the original, but perhaps I should consider this as a backup.

From 3.3mm square to D-shaft

I've bought a ton of 10mm button caps in black sandblasted aluminium. They match my larger potentiometer caps perfectly and I want to use them as potentiometer caps. Only problem is, they are meant for 3.3mm square shafts, not D-shafts, so I had to find a way of replacing the insert inside.

I've experimented with various sizes of 3D-printed inserts and this is my best result:

The inner diameter is 6.2mm, the outer is 7.9-7.95.   

7.95 works with press fit, but 6.2 inner and 7.95 outer made the part stick too hard to the shaft.

6.3 was too loose for the plastic shaft but may work on the metal one - however, there we need a section without D as the D-part is much shorter.

I didn't have time to try 6.25.

The insert height is 9.5mm. The inner height of the cap after removing the existing plastic is barely more than this. However, this seems like the perfect height - it leaves a 2mm gap on the prototype, but that prototype is 2mm lower than the button prototype, meaning that it will be a perfect match if the panel is similar to the button prototype.

The turning force necessary for the metal pot with this 10mm cap is actually ok. Quite heavy but a certain quality feel. The plastic shaft on the other hand feels a bit too light, especially when compared to the bigger caps on the metal pot. However, it is comparable to the force necessary on my other gear (Prophet 5, Little phatty) so I need to make a full mockup to try it properly.

I removed theexisting insert by 

- Drilling a 10mm hole in a wood block, then cutting it in half to make a clamp.

- I then put the clamp around a cap and inserted it into a vice to prevent the cap from rotating during drilling

- Then I drilled a progressively larger hole - 5mm, 6.5mm and finally 8mm.

LED ring update

 I got some work done on testing the LED ring with the MAX7221 7 segment encoder today, and the results are great. Both single led and multi led indicators are feasible and each has its own use. 

I tried with various lenses but my current conclusion is that no diffuser, red lense and a black panel definitely looks the best. Using a diffuser only made it look muddy.

The MAX7221 greatly simplifies the design/code. Multiple ICs can be chained, and I also think multiple parallel devices on the SPI bus are possible. One IC covers two pots with 32 leds.

I also got some amazingly good looking knobs today, matt aluminum, no indicator. Unfortunately, they have knurled, not D shaft, so it may be hard to find an endless potentiometer to fit it.