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Noob Question, led´s.

  1. Dec 18, 2006 #1
    Is it in some way possible to use a regular 100k log pot to sequentially light up something like 10 leds.

    Basically I want the pot to use led #1 while completely anti-clockwise and as i start turning it should light up #2 and 3# etc...? Does that make sense.

    I would need an array of 10 leds for the pot as I would like to use the leds as position indicators for the rotation of the pot rather then printing indicators on the faceplate.

    Im assuming this should be possible but im a complete novice.

    I just want to know if its possible , i dont mind it taking time or being a bit costly.
  2. jcsd
  3. Dec 18, 2006 #2
  4. Dec 18, 2006 #3
    Thanks that was fast ...:)

    Thats exactly what i was looking for, although i would be using a logarithmic pot , would that work for that kit?

    One more question , I might need a variation to this where the Pot would not hold the leds but as it goes to #3 it would shut off #2.

    Also on a 10 pole switch I would need it to step through the leds according to the switch.

    Any kits for that ?

    Last edited: Dec 18, 2006
  5. Dec 18, 2006 #4


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    Homework Helper

    There are voltage-to-LED-driver chips that work in either "bar mode" (all the LEDS from #1 to #n are on) or "dot mode" (just #n is on) I can't remember the part numbers - try an online catalog like http://www.maplin.co.uk

    Re the 10 pole switch, 12-pole rotary switches are common. You can insert a stop to limit them to a smaller number of positions like 10. You can have multiple wafers (independent switches) so you could use one wafer just to switch the LEDs and another one for the rest of the circuit. Or you could make a chain of 10 resistors and use the switch like the 10-position potentiometer.
  6. Dec 19, 2006 #5
    Couple more questions.

    Can i use this with a logarithmic pot and still get even distribution to the leds?

    Basically the pot is used for filter setttings on a synth and on the synth front there are markings from 1-10 and id like to replace them with the leds but i need to know that the leds will be "quantised" as i move the pot.

    What that means is that i need to match the leds to the markings, so basically the leds need to light up evenly through the pot travel.

    Any ideas?
  7. Dec 19, 2006 #6


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    Staff: Mentor

    I'm a little confused, Rolandus. It's one thing to have a pot do something like light LEDs. It's another thing to have that pot being used in a circuit for a function already (like volume control or whatever), and also have its rotation do something else like light LEDs. Are you wanting to overload the pot's function with the LEDs and still let it do what it is supposed to in the circuit? Unless it is doing something simple like setting a DC voltage (which you can then sense and turn into a set of LED drive lines), you will need to gang another pot on the shaft (which can be linear to make the LED drive easier), or gang a multi-throw switch on the same shaft.
  8. Dec 19, 2006 #7
    I´ll try to explain better...

    Im modifying a synth "Jen Sx 100" and im now designing the new front panel.
    The synth has 24 Pots ,3 of them switchable, all of the pots have a function already but I wanted these pots to control a led array as well.
    The plan was to use dual pots , one for the synth function and one for the leds.
    The leds wouls then be indicators of the pot position instead of the printed indicators on the front panel. Now I would need some way of matching the onset of a led to the position of the pot , so when the pot is set to 5 LED #5 would turn on.

    When a pot is set to for example #5 all the leds up to #5 would need to stay lit and the LM3914 would provide this.

    I need a one variation on this, one of the pots is a "tune" control centered at #5 and i would need the leds to center at #5 and then as i turn clockwise it would go to #6 etc and when anticlockwise it would go to #4 etc.

    I could use the LM3914 as long I can control it so that when the pot hits the #5 position the #5 led would light up but i imagine that is hard to achieve?

    Or ....and i dont know if this pot exists , use a dual pot with a 47k log on one wafer and a linear on the other or even a pot with a Log one one wafer and a 10 switch on the other.

    I imagine a dual pot Log/switch would be the easiest solution if it exists.
    If such a pot exists it would need to be so that the switching would not be felt in the pot action , a smooth switch.

    hope this makes sense..?
  9. Dec 19, 2006 #8


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    Staff: Mentor

    Yeah, that makes more sense. If you can find a log-linear dual pot, and use something like the LM3914, that will probably be the easiest.
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