Backlit volume knobs are a somewhat of a recent creation. There really is no functionality in it, but it looks great.
i got a hr550 receiver for chistmas, and decided to throw up a tutorial on how to do this.
Soldering iron (solder, flux)
hot glue (ultra high temp.. if you do not have a 220watt glue gun and high temp glue, skip it. the amp gets extremely warm, and melted glue and components just dont mix)
clear acrylic plexiglass sheet (cd cases will work just fine)
heat shrink tubing
(reflective flashlight bezel/aluminum duct tape optional-only for brightness)
(I unfortunatly finished my project prior to taking pictures of it, so some of the steps are already accomplished)
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Step 1: Wiring the LEDS/Power Source
You will be working with electricity that can kill you.
If you do not know how to solder, do not do it. Learn how to do what you need to do first, so you dont end up ruining the project. there are a number of 'how to solder' tutorials in instrucables.com.
If you damage something, youre on your own. The only person that should take the blame is you.
Obviously, the first thing you need to find is a power source.
I wanted the backlight to turn on when the receiver turned on.
remove the case and look towards the sirius/xm radio inputs. Both these inputs carry a low voltage power source, and is ideal for the leds.
If you are using sirius, do not tap it for power, look somewhere else.
I salvaged some leds from a rope light i bought on christmas clearance. ($1.90 for 150 led rope).
I had no idea what the forward voltage or current of them.
There is a trick to measure the forward voltage by soldering a 1k ohm resistor to the positive lead, hooking it up to a 9v battery and using the multimeter, determine the voltage. (it will drop by exacly 1k ohm) Once again, there are plenty of tutorials on how to use a mutlimeter to find these things out.
On the current factor, you basically have to take a guess. This site has a basic overview of what certain leds are:
After you find a general starting point with that information, head to http://ourworld.compuserve.com/homepages/Bill_Bowden/led.htm and plug in the info.
This will tell you what size resistor you will need.
(never mismatch leds. If you mismatch them, you may have an issue of using the wrong resistor and watching the lower voltage of the leds burn up)
I determined my leds were .60ma at 3.5volts each. (total of 3)
add up the volts-11volts total
12volt power supply
I need a resistor that is 820ohms at 0 watts
(sorry the picture quality on this isnt the best.. new camera, havent had much time to figure the settings out)
Step 2: Modifying the Knob
This was a very daunting task. The reason is that i couldn't get even light distribution over the entire knob.
It was basically trial and error.. something didn't work, scrap it and move on to something else.
The first thing i tried was to put a mirror behind knob, so the lights would reflect off of it. This failed miserably.
The next thing i tried was putting a concave mirror behind the knob. This worked better, but it still wasn't to my liking.
I then decided that i need a reflective surface that would poor the light off at an angle. So i found a flash light laying around and salvaged the reflective bezel.
If you look in the knob, you will see various ribs. in order for the bezel to fit inside the knob these had to be removed.
I started with a Dremel, and just hacked em up.
Once the light bezel was seated inside the knob, i secured it with some hot glue.
When i put this up to the receiver, the light was much better, but compared to the other leds on the receiver, not sufficiently bright enough.
My next idea came from an earlier project i did with the Logitech MX-Revolution charging base mod. Basically I cut a circle with a hole-saw from a clear acrylic cd case that would fit perfectly under the base.
I then sanded one side to give it a matte finish. (a matte finish will help distribute light better) (if it is too bright for you, then sand both sides of the cd case.
Another thing you can do to increase the brightness, is to basically turn your drill into lathe. Get a bolt and nut that fits in the hole on the piece of plastic. tighten it up until the plastic cannot be moved by hand. next, put the end of the bolt into the drill, and take a cotton cloth and hold it to the edge. turn on the drill and buff the outer edge clear. (this will take quite some time, and if you have very fine grit sandpaper (3,600-10,000 grit) this would work better.)
I had to drill a whole in the plastic behind the metal face so i could add another led. I then secured the wire with some hot glue and put everything back together.
Step 3: You're Done
Secure the clear plastic to the face of the receiver with some hot glue, put the knob back , and turn the receiver on.
You now have a cool backlit volume knob.