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LED indicators, how to design diffusion etc
LED indicators, how to design diffusion etc
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Old 22nd March 2016, 12:22 AM   #1
drewgandy is offline drewgandy  United States
diyAudio Member
Join Date: Aug 2011
Default LED indicators, how to design diffusion etc

Greetings! I'm new here but I've been lurking a few months. I hope this sparks some ideas...

I'm working on a control panel and I'm looking for ideas about how to design indicators. I have a need for each rotary knob to have an accompanying indicator light. I would love to find a way to make a lighted ring around the entire knob but that seems like it gets complicated and expensive fast. So, I'm hoping that some folks on this site might have some other ideas. I've been experimenting with shooting some basic T1 leds through some clear and/or fogged acrylic rings but it's not looking good. Not enough diffusion or end brightness.

btw, I would just put an LED through the panel just above each knob but that limits space for label tape and makes it harder to see the light when it's blocked by a neighboring knob. A lighted ring on the other hand, should be visible from almost any angle.

I guess I'm hoping that this thread might be a discussion of indicator design philosophy because that's where I'm at with this.

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Old 22nd March 2016, 06:50 PM   #2
passive420 is offline passive420  United Kingdom
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Join Date: Jun 2013
I'm with you on this. There are circular led indicators out there, I think seed studio did a slightly naff one but cannot find it now. The problem is finding one with the right amount of incremental steps/LED's.

Scroll to the bottom of this page and look at Laci's excellent LED volume indicator:

8th Note blog - audio related DIY electronics

I have his stepped attenuator and it's superb but he never really released the ring indicator to the public. But it shows what is possible.

Grab a weekend with lots of coffee and get the hang of Eagle CAD or such and do your self a PCB schematic and board layout. Easier said than done I know.

The dimming and luminescence can be controlled with an MCU - how is your arduino programming? The LED's should light up when the knob is moved, stay light showing the final position for a while then slowly fade back to a faint glow. That would be nice.
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Old 24th March 2016, 11:28 AM   #3
mt490 is offline mt490
diyAudio Member
Join Date: Jun 2010
It doesn't sound like incremental indication is being asked for which potentially makes a bit easier.

Perhaps the simplest way is to produce a diffuse as possible light behind the panel to start with, then if you put your indicator openings in places avoiding being too close to any LED underneath the light will be generally be reasonably even. Take for example:


If you want to go further, then it is possible emulate what they do inside older gauge clusters if you have photo editing software, a camera and a printer with transparent slides, and create an empirical light evening mask. If you have one handy then break into a 80's/90's VDO gauge cluster and take a look at the piece of plastic behind the gauge faces.

These days the diffusion patterns are etched in the plastic to minimise light loss, but you may not have that luxury. There are also 'backlight' panels you can buy intended for LCD's which you might be able to modify, but I suspect drilling into them to protrude knobs through will ruin their evenness.
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Old 24th March 2016, 12:11 PM   #4
sangram is offline sangram  India
diyAudio Member
Join Date: Sep 2002
Location: India
Depending on the knob design, you could think about punching a hole through and mounting the LED on the rear surface of the knob. This limits you to one indication per knob though,and the connection needs to have sufficient flex to allow the full knob rotation.

I've seen this on little hifi systems from the 90s, so it shouldn't be an issue to reproduce. Cast acrylic rod can be used as filler for diffusion/colour, and if you use two different drills the naked LED is effectively invisible.

Lighted rings should be too difficult to do with white or silver knobs/panel, you need a panel cutout that is oversized by about a millimeter compared to the knob, and recessed by a few millimeters (knob sits inset into the panel). Putting a couple of very bright LEDs behind the knob itself (but clear of your switch) will illuminate the recess quite nicely. More than a couple mm looks tacky though and begins to reveal the light source.
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Old 24th March 2016, 08:50 PM   #5
Enzo is offline Enzo  United States
diyAudio Member
Join Date: Sep 2004
Location: Lansing, Michigan
Possibly an oversized panel hole with a piece of plexiglass behind. Plexiglass to have a hole slightly smaller than panel hole, thus leaving a ring of plastic visible. bevel the edge of the plastic hole to expose the thickness dimension. Now aim lights into the edges of the plexi piece out of view behind the panel. Edges of plexiglass will glow with transmitted light from outside source. beveled edge will "glow" to a viewer out front.

if that works for you, you can even have different color LEDs lighting the thing to indicate some sort of status.

The same idea as behind these:
Edge Lit Acrylic Sign
Alro Plastics - Plexiglas® ELiT (Edge Lit Technology)
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Old 25th March 2016, 10:31 PM   #6
drewgandy is offline drewgandy  United States
diyAudio Member
Join Date: Aug 2011
Originally Posted by mt490 View Post
It doesn't sound like incremental indication is being asked for which potentially makes a bit easier.
Yes, this is just a single indicator per knob, not a position indicator for an encoder (although that would be very cool to find for a reasonable price as well).

Another piece of the puzzle that I've been planning to ask about on here: I think this whole project would be much easier if I could put all the parts on one PCB. But I haven't found anyone selling PCB blanks in 17" widths for any kind of reasonable price and all of the PCB manu houses also appear to be overly costly for anything that big. Any suggestions for 3.5" x 17" single sided PCBs?
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Old 1st April 2016, 06:42 AM   #7
mt490 is offline mt490
diyAudio Member
Join Date: Jun 2010
If you get it from the PCB manufacturing houses you'd be better off splitting it off into a multi-panel project in two sections under whatever their length limit is. Then you could use one of the per area deals (like Golden Phoenix 155 sq-in) which would probably be the best price wise.
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