Back-lit faceplate tutorial.

[szukalski]

Want a nifty faceplate with an LED which shines though? Here's how I create faceplates for my builds..

There are probably much better approaches (take Bolt Audio as an example, not sure how he's doing those but they're really nice and uniform in intensity). My approach is to try to make it as easy as possible, which means standard 5mm LEDs..

Let's start with a PCB. Having a standardised layout is REALLY FUPPING HANDY. I follow the PPCB standards (25.4mm vertical gap between layers, 33mm horizontal gap for 4-knob, 20.3mm for 6-knob) and usually add the LED on a 3rd vertical layer.

I take my center point from the middle of a 125B, you do you.



It's important to remember that when you layout the PCB, pads for the potentiometers will be 16mm below where you want the shaft. (Where you want the shaft. Naughty). Let's look at an example. We'll have a row of pots at +38.1mm, +12.7mm, and the LED at -12.7mm:



So now, let's create a faceplate. Let's start with the edge cuts and graphics layer already there. I have added an 'x' to show where the LED will be.



To let the LED shine through, we need to have:

• No copper layer.
• Remove the front and back mask.

This means that we need a footprint for the front and back mask layers. I have an image I want to use so I use KiCad's image converter to turn it into a footprint. I aim for 12-16mm wide, but you may have to make it a little larger if you have whitespace around (like I do). The black lines will be what is taken away from the mask. You may need to invert the image with the "negative" check box like I have.

Important to note that I am exporting a footprint in the F.Mask layer.



Opening KiCad's footprint editor, I import the footprint:



I also want the same for the back mask, so I duplicate the footprint, go "Edit > Edit Text & Graphics Properties", select "Graphic items" as the scope, and change the layer to "B.Mask". Apply and close:



Yay, back mask!


Now add them to the PCB in the same location..

 

[szukalski]

You can review the faceplate and see that it's got the same image on the back and front:



If you just took the font mask footprint and changed the layer by flipping it, then it'd be mirrored and wouldn't align up with the image on the other side.

You can also just make a circle or square on the back mask, but having the same image makes the backlit better defined.

 

[szukalski]

Now, it's time to order at JLCPCB (or your vendor of choice).

Nothing special to do, I would recommend doing a thinner PCB than normal (0.8 or 1mm), and putting in a comment to ignore the connectivity because it'll fail a default check (there's no copper layer after all).

 

[phi1]

Woah that is super cool. I have tried this concept with a printed faceplate from AmplifyFun. Light bleeds through the printed black ink. Great to have another idea.

Is it bright enough to function as the ON indicator?

would the light shine through a white silk print layer? Or do you only do the bare board without resist.

 

[almondcity]

This is awesome, thanks!

 

[szukalski]

Is it bright enough to function as the ON indicator?

would the light shine through a white silk print layer? Or do you only do the bare board without resist.

I use a 3k6 or 3k3 for the CLR to get it a little brighter, but you can easily see it through. It's my default for indicators now. Makes boxing at least 15% more enjoyable.

If you have a mask layer item, then it works as an inverse, taking away the mask in that location. It also means that there is no silkscreen layer there either.