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adding an LED to a knob

post #1 of 8
Thread Starter 
for grins and giggles I wanted to try to mod my knob

this knob came from a behringer a500 amp. it looked ugly on that amp but it can look OK in the right context. I'm hoping

here's the knob, untouched, on my amp before the surgery:

it looks ok and it matches. but it can be better.

here's the process:

cut a small square hole in the knob. I started the hole with the hot tip of my soldering iron and then used an xacto hobby knife to whittle away the plastic until it was as square as I could get it. keep trying with your target LED so that you don't take too much plastic out.

from behind, use glue (I like hot-melt) and secure that sucker in there:

use flexible wiring. this shows wire-wrap wire but my later version has a pair of ribbon cable wires that are multi stranded. I'm hoping that will stand up to the repeated flex due to turning the knob.

does it work?

...it seems to work

to finish the job you simply drill a very small hole near the shaft of the pot (on the front metal chassis) and be sure it clears the back of the pot as well as being 'inside' enough so that the knob will fully cover the wire.

wrap the wire enough the shaft of the pot so that lock-to-lock rotation does not bind the wire and it stays inside the confines of the hollow knob body.

end result:

what you can't see from the pics is that the pot is a *motorized* pot and so when you use a remote control and turn the pot, its quite a neat effect to have the LED 'point the mark' out for you

part 2: I intend to use that LED in a creative way. to be continued....
post #2 of 8
That looks great!
But I would really recommend you put heatshrink on the exposed part of the red lead (ie. across the resistor and right to the LED).
post #3 of 8
Thread Starter 
I might insulate those wires later. maybe some more hotmelt. one thing I want to be sure of is that no *connection* is being flexed. wires in the plastic is ok but if its not the plastic and only the metal that is being 'hinged' then it will wear out eventually. if I glue enough of the wire down, I think that will strain-relief it better than not doing that.
post #4 of 8
Love the red LED. Thank you for not using blue
post #5 of 8
moar info on motorized pot? Sounds like something that will do a lazy person good.
post #6 of 8
Thread Starter 
the motorized pot was taken from an old sony cd player! about 10 or 15 yrs ago. something told me to save that one part and it did come in useful:

turns out (heh - that was a joke) that the pinout is the same as the pany pots so the pimeta was easy to adapt to this pot. it was simply a linear line-up of ribbon cable.

to make the pot work you simply run +5v to the 2 rear power tabs. to turn it the other way you reverse polarity.

I have 2 relays that take +5v and when you send power to 1 relay it turns the pot one way and power to the other one reverses it.

I have an IR module that decodes remote button presses and generates a single TTL line out signal that I then put thru some LAA110 solid state relays that finally end up driving the motor relays:

sadly they don't give you a board - only the parts - so you have to wire the receiver board entirely up yourself.

there it is with 2 debug LEDs showing when volume up and down are pressed.

kit for remote was from:


search for k92

as for the motor pot, I wonder if its still buyable from sony parts. sony used to sell repair parts directly to end users. the parts were affordable, too.


post #7 of 8
Thread Starter 
part 2 now works and was a worthwhile upgrade.

after adding the fancy LED in, I wanted to make it show more than just 'power on'.

I also wanted to mount a crossfade board inside and control it.

but there's only 1 led and no more panel room for switches or more leds!

what to do, what to do.

brainstorm: use that single led and the IR remote to create extra 'knobs for nerds'

the idea: dedicate one button on the IR remote and tie that to a 7474 TTL flipflop. press on, you get one state, press again, it flips states. that will be my crossfeed on/off selector.

so, we map one of the IR buttons to this flipflop. the flipflop drives a relay so that its latching. that relay has 3 poles; 2 poles for the crossfeed on/off features and 1 extra pole to show the LED in FULL BRIGHT or dim modes. that's it! the 2nd relay pole shorts out a series resistor (or doesn't short it out on the other end of the relay throw) and this simulates the bright/half-bright nature of the led.

crossfeed off, led is dim (but still visable across the room). you also know power is on.

crossfeed on, led is very bright and you know power is still on

rotate volume control with IR remote and the built-in led follows it along. you can easily tell, at a glance, where your vol level is. the rectangular shape of the led is enough to give a good indication of what angle the pot is at.

its very cool, even if I do say so myself. I'm using this remote armchair crossfeed on/off all the time now. its useful to have and I would not want to perm fix the CF on or off - it really does need to be selectable and it does seem to have diff effects (good or bad) based on the content of music.
post #8 of 8
You, sir, are a DIY'er's DIY'er. Excellent work!
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