Diffusing light within plastic?

[AdeV]

I've been hard at work (ahem!) making a new switch for my doorbell. I got fed up with the old cheapie mechanical switches forever failing; and I'm not about to buy an expensive one when I have a workshop full of tools, aluminium and lumps of plastic lying around. Especially not when I get to play with electronics too 

So I designed myself a touch-sensitive doorbell. A small aluminium disc with a wire going to an ATTiny single-chip computer, a few other odds & sods, and you have a touch sensor, which normally shows a white LED, and changes to blue when you touch the sensor (the bell also rings, as almost a side thing). Got all the electronics up & running and today I finally got round to making the plastic bits of the switch.

What I want to happen is a sort of "angel eye" effect around the sensor, a nice fairly consistent ring-o-light.

What I'm getting is an obvious bright light on one side, or the other, depending on which LED is lit.

See the pictures below, and it should be obvious what I'm on about... even though there's no outer box yet.

Obviously I need some kind of diffuser arrangement, but how does one create such a thing? I tried filing the tops off the LEDs (no improvement), roughed up the top plastic surface a little (no improvement); I could rough up the underside, except that's a bit tedious... I could re-arrange it so the LEDs are pointing at the sides of the plastic contraption, thus not shining directly on the surface; or I could just put them further away, so they're not directly under the ring... Any more ideas (especially if you KNOW it'll work) welcome. Note that I don't have a lot of room to play with, so if I have to put multiple LEDs in, it'll have to be SMD.

[chipenter]

Have you room to put a polished refleting ring round the leds .

[PK]

Assuming that the circuit will go in a box. Try using two or more leds NOT pointing up at the plastic ring. Make the inside of the box as reflective as you can.  When you are staring at it on the bench it won't seem bright enough. But in place it may well be fine..

Worth a try I reckon.....

PK

[SwarfnStuff]

OR, try (if there's room) putting a ring of opaque / translucent plastic between the LED and bottom of sensor. Perhaps this will diffuse enough light to make the light more even???
John B

[Mike E.]

For diffusing the light, here is a possible solution. Items needed are....... a black plastic cover from a pen or sharpie marker which would fit over the LED, a cap from a suitable plastic bottle cap cut to fit around the ringer button, and a few fibre optic strands. (possibly from one of those novelty lamps).

1.) Drill tiny holes around the plastic cap and the pen cover  for locating the fibre optic strands.
2.) Punch out the center of the plastic cap and split it to fit around the ringer button.
3.) Feed the fibre optic strands through the plastic cap, glue in place with a drop of super glue from the back side, then cut flush with the face side when dried.

The optical effect should be star like around the perimeter of the button. Here is a rough sketch, hope this helps.



 

[lesterhawksby]

Flatting/sanding the LED ends causes light to start diffusing out there, but if you can still see the LED end, it'll still look like a point. You could use a separate diffuser (eg sanded bit of clear plastic) a bit further away onto which they both shine.

Mike's suggestion of fibre optic strands is cool but maybe tricky. If you have any sheet acrylic scrap, maybe cut a "Y" out of it and polish the ends so it works as a light pipe? (not super shallow though)

If there's room, it might work to have both LEDs point backwards onto a bit of white plastic which serves as the apparently illuminated surface. Or sideways and have the white plastic as an angled reflector, saving case depth at the expense of width.

If you ARE prepared to go SMD you can probably just make the two so close together they are hard to tell apart...

I assume buying parts to make it look super fancy is out of scope, but if not, there are some lovely RGB LED rings out there...

[AdeV]

Today, I got back in the workshop for the first time for a few weeks... so I had a go at re-doing my "light pipe". This time, I've just flattened the sides a bit (didn't quite get it centered, but then I wasn't measuring). Laying the LEDs over is the trick, I think, so now they shine into the sides that I've cut. Adding some black tape (in the final version I'll use paint) cuts out the point glare pretty much entirely. 

My original circuit had the computer & the various resistors in the same housing as the LEDs (the bit that'd live outdoors, on the side of the door), but turning the LEDs means I don't have room to do that any more, so there'll have to be a separate box inside with the electronics - no biggie for me, and it also means the IC is inside, so I don't have to worry quite so much about weatherproofing it.

So, that's pretty much the last piece in the puzzle; now I need to make the aluminium outer box to cover the whole contraption, make another small circuitboard to hold the LEDs & light pipe & sensor, and find/make a suitable box for the indoor electronics. Hopefully by the end of the weekend I'll have a working doorbell again!

[RussellT]

Brill!

I bet, like me, you're always wondering why you never have time to do stuff. 

Russell