Monday, February 2, 2009

Power Switch and LED Indicators

One of the good things about using the white plexiglass is that the LED hard disk and power indicators can shine directly through - giving quite a nice effect.
So overall there will be a large power switch/with LED in the center of the front panel, and the hard disk activity LED directly below, as shown.

Looks simple from the front - but from behind it ends up being rather complicated :-(.
Here is what the design looks like.

At the top of the sketch, there is the 'button' pieces - which consist of a round disk of plexiglass, glued to a small back plate for attaching to the case. I havent worked out how to etch a nice 3/4 circle with a vertical line through it, like the usual power supply button.
I am going to try and build the button myself, rather than using the commercial power button that I bought before - to see if the whole case can get a consistent look and feel.

In the middle of the sketch is a top view of how the button piece attaches to the case. There is basically a frame of plexiglass pieces that hold the button in place. the button slides backwards and forwards on un-used pop-rivet legs on either side of the button. The springiness of the button is to be provided by the actual power switch itself. Another option to give additional bounce is to grab the spring out of a normal ball point pen with the click in/click out feature, and put some short pieces of the spring on the rivet runners... however this is probably not really necessary. The power LED will be inserted into the button piece of plastic directly.

At the bottom of the sketch is the hard disk activity LED. There will just be several layers of plexiglass with a hole drilled through the middle and the LED poked in.

One final piece of the design is some included metal supports that attach to some wooden uprights that will eventually connect to the top and bottom metal plates for rigidity.

Anyway - the plan is to firstly build a prototype of the button assembly, just to see if it works as planned - then I can attack the actual case.

Firstly I started off cutting the circular piece for the button. This was done by drilling multiple holes around a circle drawn on the plexiglass.

I then filed off the rough edges to make a roughly round shape.

For the back piece to be glued to the button, there were some choices to be made. Is it best to simply drill a small hole in the back piece to stick the LED into, or is it better to have a large-ish open cavity against the button piece in order to diffuse the light better across the back of the button perspex... I tried both to see if there was much of a difference

The one on the left shows simply a directly drilled hole (at around a 45 degree angle). The one on the right used a large drill bit to drill a 'cavity' on the front face, and then drilled a small hole through to the back at around 45 degrees - the LED would be stuck through this hole. i.e. the results look like the following with the LED inserted.

With the front button piece in place, I feel that there is better diffusion of the LED light with the cavity approach... However the result is still a little short of ideal. Not sure how to get a better distribution of the light evenly across the whole button.

I then moved on to cutting a prototype hole for the button in a sheet of perspex. Seems that for the real thing, I will have to focus on getting the button and holes as round as possible - otherwise the result is a little Flintstone-esqe - i.e. like the stone wheels on their cars :-)

I then did the embedding of some nuts into some plexiglass - easier than expected.

And fitted it all together. The second shot shows with some oversized springs included to get the idea of how additional 'spring' can be added to the button.

Next was attaching the whole frame to the main piece of plexiglass. With this done, all the construction was basically done. What remained was the assembly together. Note that one of the 'features' of this design is that the majority of the complex workings are not attached/related to the front outer case plexiglass. i.e. all of the button sliding mechanism, the placement and holes for the hard disk LED, etc... the advantage of this is that it can all be replaced with a new set of workings, with a low likelihood of needing any reworking of the outer case plexiglass.
Here are all the bits ready for assembly.

Which when assembled looks like this from the front (simple), and this from the back (complex).

Note that when inserting the power switch, you need to dis-assemble and feed it into place - key is the slot cut for feeding the cable through.

Now with everything in place, and the system powered up in full household lights on mode, you get the following...

And with the lights progressively dimmed down...

The red LED is brighter than the green, and bleeds into the green's area.

I tried reducing the red lights spread - it seems to completely illuminate the surrounding plexiglass - I wrapped the LED in some aluminum foil as such.

Which has the overall effect of reducing the red to a similar level as the green (compare with the 'lights out' picture previously).

The bleed into the green's area has been stopped.

With this configuration, under 'normal' lighting, the result is as follows.

Which seems to be acceptable I think.

It is worth noting that the green LED is a little duller than ideal. Seems that there is a lot of light comming out the back side of the case...

One thought is to glue a layer of aluminum foil to the back of the button, to hopefully reflect more of this light forward to get a better, even spread of green light over the button.

Anyway... in summary.

Generally OK with the design - a bit chunky... and there are some fine tuning to be done to improve the effect...
  • Try some aluminum foil on the back of the button plastic to give a brighter button, with more even light distribution.
  • Button is a little 'sticky'. Try some additional springs - does it help ? And also try flange-ing out the holes where the rivet stalk goes through the plastic.
  • Drill the hard disk activity LED holes smaller (red LED), and experiment with the aluminum foil effect.
  • Be more accurate with the roundness of the button and hole...
And finally - need to look into the polishing of plexiglass - how best to finish the edges of the button and hole.


  1. Polishing the plexiglass won't be easy with that sized hole. When we worked with plexiglass at school we progressively sanded the edges using wet and dry sandpaper getting finer as we went. This gets the scratches out. For the actual finish, we used a waxed buffing wheel (see They're an attachment for an angle grinder. A bit too big for your hole, but you might be able to find a similar implement for a small rotary tool?

  2. That buffing wheel would require a rather large on/off button hole :-)

    Dremel seem to have suitable products - anyway - will see if it is really needed later.