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LEDs for amp footswitch

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by aleclee, May 7, 2005.

  1. aleclee

    aleclee TGP Tech Wrangler Staff Member

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    I want to build a footswitch for my amp's boost and channel switching. I have the TRS thing figured out but would seek wisdom on LEDs. Most of the ones I see at Rat Shack are either 2-2.5V or 12V units. Is that all that's commonly available? Like most amps, mine uses the 6V tap for the footswitch.

    Should I run a 12V LED under voltage or would you suggest using resistors to drop the voltage to a 2V LED? Schems for this would be greatly appreciated!

    Thanks [​IMG]
     
  2. Slick51

    Slick51 Colonel Curmudgeon Silver Supporting Member

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    Use the 2.5 volt one and a dropping resistor. The math goes like this...

    V = voltage in volts
    I = current in amps
    R = resistance in ohms

    so V=IR, or in our case the difference in the voltages, delta V, is what we'll calculate. Solving for R, we get R= delta V/I.

    The power available is 6 volts, so 6-2.5 = 3.5 volts that need to be dropped. The nominal current in a typical LED is 20 milliamp, or .02 amps.

    Divide the 3.5 volts by .02 amps and you get 175 ohms, so you have to have a resistor this large to keep from burning the LED out. I usually put a resistor in the 300-450 ohm range in to be safe. This resistor attaches to the anode side (+). If you look at the LED carefully, on the perimeter of the LED there will be a flat spot. The leg next to the flat spot is the cathode (-). Attach the resistive load to the other side. That's all there is to it.

    Go here for schematic help.

    HTH
    Slick51
     
  3. Slick51

    Slick51 Colonel Curmudgeon Silver Supporting Member

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    Thanks. I receive so much great info here, when I have info to pass on, I'm tickled to add to the info pile. :D

    Slick51
     
  4. aleclee

    aleclee TGP Tech Wrangler Staff Member

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    +1. Just what I was looking for!

    Thanks so much.
     
  5. Thames

    Thames Member

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    Ok.. If I want to install a LED in my fuzz box, which one should I go for ?
     
  6. Slick51

    Slick51 Colonel Curmudgeon Silver Supporting Member

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    I need more info...what LED? or color, size, shape?. You can use essentially any LED with less than 9 volts for the forward voltage (Vf). The resistor is what we'd have to calculate to match your choice.

    HTH
    Slick51
     

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