Addressable RGB LEDs (HD107S) as PCB indicators (lightpipe and other factors)?

[kreyszig]

Hi,

I am thinking of using addressable RGB LEDs (HD107S or HD108) as configurable PCB indicators. They are mostly available in 5050 size, but they are also available in 2020, and rarely in 3535. 3535 would be my favorite choice, but it seems difficult to get a hold of them. The 5050 size seems a bad choice for compatibility with light pipes. So size 2020 is the remaining option.

Is it a bad idea to use a light pipe with a 3.5 mm lens (e.g. 515-1020F https://s3-us-west-2.amazonaws.com/catsy.557/Lightpipe_Selector_Guide_D.pdf) with a smaller LED?

Other than fact that they are RGB, I like how easily these can be driven with any external buffer driver or current source, so they seem like a natural choice as indicators. What do you think?

Thanks!

[kreyszig]

Maybe these https://www.mouser.com/datasheet/2/50/PLW5_XXX-3001513.pdf would allow me to stick to the more widely available 5050 version (the HD108 seem to be only available in 5050)?

[tooki]

Using a smaller LED is no problem. If anything it’s desirable because it gives you more tolerance for positioning inaccuracy. What you do want, as much as practical, is to minimize the gap between the light pipe and LED. Like… you want a half mm or so for positioning tolerance, but beyond that, the larger the gap, the more light can exit laterally and illuminate other segments.

I recently used the panel-press-in light pipes for the first time. Worked great, but to have them spaced closely as I did, I did find it necessary to prevent optical crosstalk by slipping black heat-shrink tubing over the pipes after insertion. (I then used a fine hot air nozzle to ever so slightly shrink the tube right next to the panel. (Heating it at the open/PCB end would cause the tube to shrink over the end of the light pipe, which I didn’t want.)

[kreyszig]

Thank you, it makes sense