LED Articles for Noob

[cacibi]

Looking for links to articles on incorporating LED's into DPDT footswitches.  Basically, I want to incorporate Dragonfly's dual volume mod into a Tubescreamer build, but am not sure how to add an LED that indicates when the second level pot is selected.

I think I've got an idea how this would work based on the distortion boost mod at the Beavis audio site:

http://www.beavisaudio.com/Projects/ScreamerLab/index.htm

So - instead of the 4.7k resistor, I would add the second level pot to the other side of the DPDT switch, the lug 1&2 pads on the board would run to the switch at lugs 5 & 8, then to lugs 1&2 on the pots.  9v power would go to lug 3 and lug 2 would go to the 4.7k resistor and LED.  But I would still like to do some reading to understand all of this  - like why there is a 4.7k resistor before the LED.  Figuring it out is always less important than knowing the hows and whys behind it for me.

Thanks

[petemoore]

  Looks like they're choosing 4k7 as the value to reduce current through the LED [so it don't burn up], depending on which LED, I've used 3k3 for brighter, 4k7's when I just want light and don't want to think about a little brighter...
  GEO...Millenium Bypass is where to look for DPDT /w/ LED info.

[dano12]

The 3PDT switch is just like the 2PDT shown in Dragonfly's volume mod--it just adds another set of poles. Wire up the switch as shown in Dragonfly's diagram, and then add the LED circuit to the third set of poles. This diagram shows the details:



As for the 4.7 k resistor, it is used to limit the current to the LED. You don't want to stick your average LED directly onto a 9 volt source or it will burn out. As Pete said, 4.7k gives a medium brightness, 3.3 a little brighter, etc.

Hope that helps.

[cacibi]

Perfect - much appreciated!