Frontplate design w LED light channels, help needed

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weasel79
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Frontplate design w LED light channels, help needed

Post by weasel79 » Sat Jun 08, 2019 6:10 pm

hey guys, i'm shamelessly crossposting my post from the midibox forum cause i am sure there are a ton of frontplate/material experts around here... i am building a desktop keyboard synth with these nice rgb led ring encoders, in a tiny form factor:
Image
most recent demo video:
https://www.youtube.com/watch?v=FaMVOi2yt4E


So i am currently investigating frontplate options and i realized some small issues with these 2020 LEDs: they are in a completely transparent housing, as opposed to the white housing with a top lense of the 5050 2812s. So naturally i get quite some cross bleed between the neighbouring LEDs, at highest brightness setting even up to 2-3 LEDs far. In real life it is not nearly as noticeable as on those videos i posted but i am still trying to optimize it.

Following are some sketches of what i have so far and some ideas. The "light channel" drill holes got pretty long, 3.5-5mm over all, but that actually makes frontplate assembly super convenient and also should reduce the cross bleeding by creating a more narrow viewing angle. any input is welcome!

1. This is a description of what you see on the videos, what i started out with. just a 3mm mdf with 1.25mm holes for each LED, and another 1.6mm acrylic layer on top, same holes. they align nicely and sit right on top of the middle of the LEDs. The thin arrows show where i think most of the crossbleed comes from. the whole housing of the LED is transparent resin so the 3 tiny R G B LEDs all emit light in any direction of almost half a sphere.

Image


2. So the first thing i tried to improve it was to cut a negative mask out of MDF to enclose each LED, leaving room for the condensators and solder points.

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its black coated MDF and obviously the details are a good bit too much for the laser. but i am sure i could still improve on these first tries. it did improve the bleed a little but not to the extend i hoped for.




3. i tried the same technique but with black cardboard instead of the MDF, and the little bridges betwees the LEDs came out even better.

Image

Image



4. the next thing i want to try is different materials. i did a first cut of the same negative mask as above in solid acrylic but didn't get to test it yet. i have to play with the lasercutting margins and measures to make the fit as good as possible, eg. i left space for the extra solder points but not for the blobs of solder around the LED connectors. but right now i am more interested in alternative methods. what about using milliput or some other thick epoxy stuff, press it on the LED pcb so the top stays somewhat clear, and carve off remainders after hardening? something like this: (note: most likely my final front-frontplate will be aluminum..)

Image

anybody has experience with using milliput/expoy like this?


another thing to try is the resin-based 3d printer in my local fablab which might be detailed enough to get a better mask going.

and yet one more idea is to get some thick lightproof acrylic paint and a tiny brush and try to paint the sides of the LEDs, or even spray paint it with circular masking tape on the top?



also i am not sure about how to fill the light channels in the frontplate, what @Antichambre did so beautifully with those inlays. i was also gonna try just fill them with epoxy and razer off any residue on the outside? or maybe get some 1.25/1.5 mm optical fibre, and stuff each LED hole with a 3-5mm piece that ends directly on the LED enclosure? might also help reduce bleeding.



Here are some more pics of @FantomXR's beautiful prototype SMD assembly job, you can see the shape of the LEDs really good. in before questions: shot on iphone with a 10$ hama macro lens i just bought on impulse at the local electronics megastore. keep in mind these LEDs you see are 2x2.2mm small...

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oh and see my other thread if you wanna jump in on the group order for these.

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cackland
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Post by cackland » Sat Jun 08, 2019 11:50 pm

Have you looked into light pipes?

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jochem
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Post by jochem » Sun Jun 09, 2019 1:31 am

I think i would use some heat resistant sealant to seal off the sides of the leds. Than you can use the mdf layer on top of that (after the sealant has dried).

You should be able to find a sutable sealant with a thin dispenser at a local car supply shop. It is commonly used as a gasket solution.

weasel79
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Post by weasel79 » Sun Jun 09, 2019 5:11 am

cackland wrote:Have you looked into light pipes?

Image
yeah those look like what i meant with the optical fibre, these look super convenient though, thanks. they should help with the directly emmited "right" light, not with the bleed i guess? any idea if they exist specifically for 2020 leds?
jochem wrote:You should be able to find a sutable sealant with a thin dispenser
good call, i will look into those. would you use a brush or spray paint? how thick/liquid is that stuff? keep in mind these are 2mmx2mm and i can't paint them before assembly.

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whoop_john
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Post by whoop_john » Sun Jun 09, 2019 5:45 am

How about a small piece of black heatshrink over each LED? A lot of work I guess.

I'd probably use a 00 size artist's brush and black acrylic paint.
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Post by jochem » Sun Jun 09, 2019 10:16 am

The heatresistant gasket sealant i mentioned is like toothpaste.
It comes in a toothpaste like tube with different tips or in a thin can. It is mostly black en you dispense it on the object directly.

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ersatzplanet
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Post by ersatzplanet » Sun Jun 09, 2019 11:25 am

weasel79 wrote:
cackland wrote:Have you looked into light pipes?

Image
yeah those look like what i meant with the optical fibre, these look super convenient though, thanks. they should help with the directly emmited "right" light, not with the bleed i guess? any idea if they exist specifically for 2020 leds?
jochem wrote:You should be able to find a sutable sealant with a thin dispenser
good call, i will look into those. would you use a brush or spray paint? how thick/liquid is that stuff? keep in mind these are 2mmx2mm and i can't paint them before assembly.
Light pipes work very well with isolating external light sources. At least some designs do. The nature of some of them, having a high incidence of reflection, means external lights not at the correct angle, reflect off the sides instead of going "through" the cylinder. Typically the light has to enter the ends to travel down the "pipe".
-James

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weasel79
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Post by weasel79 » Sun Jun 09, 2019 9:28 pm

ersatzplanet wrote: Light pipes work very well with isolating external light sources.
Do you have any good source for tiny ones? Anything 1-1.6mm diameter. mouser etc start at 50ct/pc, i need hundreds-thousands...

also ordered that gasket sealant and some other epoxy variants. second day of lasercutting today was better but i don't think it'll be good enough. might try and mill a light pipe mask out of transparent acrylic with cnc.

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extralifedisco
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Post by extralifedisco » Mon Jun 10, 2019 5:40 am

Wow, nice work so far! Here's some very basic stuff - this product training module on digikey explains the geometry of fitting lightpipes on SMD leds:
https://www.digikey.com/en/ptm/l/lumex- ... g/tutorial

The gist of it is that you want the light pipe to have a reflective surface on at least 3 sides of the LED which bounces the light up towards the panel, which gives you less bleed.


It may be worth picking up and older Akai/ableton APC40 which has nice LED rings and a custom "light pipe" part. You can see in this picture there's a black plastic ring with lots of tiny channels for SMD leds on the board. There's clear plastic pieces coming through the panel but I don't know if that's a separate part.


(If that hotlink doesn't work try the 5th pic here:
http://archive.monome.org/community/dis ... rt/p1.html)

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ersatzplanet
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Post by ersatzplanet » Mon Jun 10, 2019 12:10 pm

weasel79 wrote:
ersatzplanet wrote: Light pipes work very well with isolating external light sources.
Do you have any good source for tiny ones? Anything 1-1.6mm diameter. mouser etc start at 50ct/pc, i need hundreds-thousands...

also ordered that gasket sealant and some other epoxy variants. second day of lasercutting today was better but i don't think it'll be good enough. might try and mill a light pipe mask out of transparent acrylic with cnc.
I'm afraid to say that in most cases, for the density and use you have in mind, it is a custom piece. This used to be an extreme expensive process with the molds costing lots of cash up front, but the cost are much more palatable nowadays. You may, if you plan on doing quantities, get the cost pretty reasonable.

I have to say though, I think the easiest and most cost efficient thing to do is live with the bleed. It is not like the bleed makes the unit unusable, the user will know the settings still. Alleviate it as much as you can with the methods you have shown above, and live with the results. It will always be cheaper.
-James

James Husted - Synthwerks, LLC - www.synthwerks.com - info@synthwerks.com - james@synthwerks.com
Synthwerks is a proud member of the Mostly Modular Trade Association (http://www.mostlymodular.com).
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Post by soundshaper » Thu Sep 05, 2019 7:43 pm

weasel79 wrote:
ersatzplanet wrote: Light pipes work very well with isolating external light sources.
Do you have any good source for tiny ones? Anything 1-1.6mm diameter. mouser etc start at 50ct/pc, i need hundreds-thousands...

also ordered that gasket sealant and some other epoxy variants. second day of lasercutting today was better but i don't think it'll be good enough. might try and mill a light pipe mask out of transparent acrylic with cnc.
Did you determine a good way to do this? I'm doing something similar right now and found this thread. Check out these parts.

https://www.alibaba.com/product-detail/ ... 60402.html

https://www.alibaba.com/product-detail/ ... 95378.html

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Post by fingerfarbensound » Thu Sep 05, 2019 8:12 pm

Can you get access to a SLA or even better Polyjet 3d printer?
If so you could simply 3D print a ring that fits around the LEDs and has wedge shaped protrusions on the inside.
Make it out of black resin and it should block out the stray light.

Of course if you're at it you could even print an additional piece that fits over the LEDs and in the holes and functions as a custom lightpipe... out of clear resin.

Alternatively:

You can actually evaporate acrylic paint using a co2 laser.
So you would paint over the whole ring with black acrylic paint and then user the laser cutter to remove the paint on top of the LEDs

possible pitfalls include: Misalignment, damage to the LED housings, much, much trial & error with different paints, thickness & laser settings.

Also you might be able to just do the paint thing as remove the paint with a q-tip and a little acetone.

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cackland
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Post by cackland » Thu Sep 05, 2019 11:28 pm

Yeah, the other alternative was 3d printing a ring plate around it all.

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soundshaper
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Post by soundshaper » Fri Sep 06, 2019 6:09 am

All great ideas. Yeah the custom printed/molded black ring is the best solution. I put links to those two light pipes specifically because they are only 1.5mm and 1mm diameter, which is crazy small! Those are hard to find. It would also be worth considering using LEDs with a very narrow viewing angle, like 30 degrees or less.

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Altitude909
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Post by Altitude909 » Fri Sep 06, 2019 6:24 am

+1 for just paint the sides of the leds

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cackland
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Post by cackland » Fri Sep 06, 2019 7:16 am

Altitude909 wrote:+1 for just paint the sides of the leds
Not a bad idea, however this could get very tedious if a larger production run was required.

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Altitude909
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Post by Altitude909 » Fri Sep 06, 2019 7:21 am

cackland wrote:
Altitude909 wrote:+1 for just paint the sides of the leds
Not a bad idea, however this could get very tedious if a larger production run was required.
If that's the plan, he should be looking for different parts. An over-complicated fix for part that doesnt really work for the application is always the wrong way to go.

What about putting the LEDs on the back of the PCB in a cutout

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Post by fingerfarbensound » Fri Sep 06, 2019 5:05 pm

The paint solution might work on a large run too.
Just use a stencil like you certainly have for the solder paste so only the parts between the leds gets paint.
Probably needs a custom jig though...

Of course in the long run you'd might just bite the bullet and go for another type of led that has a plastic housing.
I have these 2121 so you'd have to change the layout and make the ring 5% larger...
https://www.aliexpress.com/item/32494272574.html

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Post by t-b » Sat Sep 07, 2019 4:47 am

For the smr diy build, i used 3mm pmma optical fiber, works very well and cheap
there is several diameter

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Post by weasel79 » Sat Sep 07, 2019 11:42 am

i exxperimented a lot with lasercut seperators a shown above. my next step would have been to try and 3d print custom transparent light pipes, and a "negative" black solid separator piece. but funny enough just a couplee days ago i also finally discovered those taobao/alibaba light pipes at reeasonable prices, so, i am ordering some of those now and will report back. my led ring pcbs finally are waiting at local customs for clearance too, so i'll be back soon..

there's some more small diameter choices and lengths on taobao:
https://item.taobao.com/item.htm?spm=a2 ... 6071225474

if those pipes are not good enough against the cross bleed i will try adding that "negative" 3d printed separator element. paintingg the sides manually would be too much, with 1500 LEDs per keyboard. also i don't think i'll receive a soldering stencil as i ordered fully assembled PCBs...


edit. fwiw i also tried optical fibre and while it worked pretty well it was hard to get a really clean cut. tried all kinds of blades/pliers, but i couldn't get a decent enough flat surface on my led rings with them.
Last edited by weasel79 on Tue Sep 10, 2019 4:51 pm, edited 1 time in total.

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Post by Agawell » Sat Sep 07, 2019 11:59 am

if you are buying thousands then it might be worth going directly to the manufacturer - if you can find them - rather than buying from mouser or even alibaba
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