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Musical LED's

Discussion in 'Electronic Basics' started by Rob, May 30, 2006.

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  1. Rob

    Rob Guest

    I'm in a third-world country and have limited resources. I want to be
    able to create a "sound meter" out of 8 or 10 LED's which could be
    connected to the amplified line that leads to the speakers. The only
    electronic parts I have are wires, capacitors, LED's and transistors. I
    have used capacitors and transistors before for my woofers and
    tweeters, but now I want it all to look good. Any suggestions?

    ---P.S. This is my first day and first post.
     
  2. I don't have anything specific, but it is doable. Using ICs to
    drive the LEDs simply makes it more compact.

    The basic idea is to rectify the incoming audio signal, and then
    feed that varying DC voltage into a string of voltage comparators.
    When the audio signal goes above the trip point of a comparator, the
    LED on the output goes on. If the audio goes up further, then the
    next higher comparator goes on, and so on. (Some of the ICs may
    add to this, with locking mechanism so only one LED is on at a time.)

    You can make comparators with transistors. I suppose you could even
    get away with a single transistor per comparator, doing something like
    a positive voltage on the emitter so the input voltage has to rise
    above that trigger voltage, but it probably is better to use a couple of
    transistors per comparator. This sort of circuit used to be common before
    ICs became common.

    Maybe someone else has something specific. Old books likely have this
    sort of thing, too.

    Michael
     
  3. BobG

    BobG Guest

    I think you are going to need some resistors and a pot or two. Got
    those?
     
  4. John Fields

    John Fields Guest

    ---
    Welcome to the group. :)

    You can't get resistors in Belize?

    Or comparators?
     
  5. Mike

    Mike Guest

    What about a string of diodes driving some transistor switches,
    something like the circuit in the SwitcherCad file below?
    Also posted in a.b.s.e. as a pdf.


    Version 4
    SHEET 1 880 724
    WIRE -112 160 -112 0
    WIRE -16 0 -112 0
    WIRE -16 32 -16 0
    WIRE -16 128 -16 96
    WIRE -16 144 -16 128
    WIRE -16 240 -16 208
    WIRE -16 256 -16 240
    WIRE -16 352 -16 320
    WIRE -16 368 -16 352
    WIRE -16 480 -16 432
    WIRE -16 528 -16 480
    WIRE -16 624 -16 592
    WIRE 48 480 -16 480
    WIRE 64 128 -16 128
    WIRE 64 240 -16 240
    WIRE 64 352 -16 352
    WIRE 176 128 144 128
    WIRE 176 128 176 64
    WIRE 176 352 144 352
    WIRE 176 416 176 352
    WIRE 176 480 128 480
    WIRE 176 624 176 480
    WIRE 240 64 176 64
    WIRE 240 240 144 240
    WIRE 240 416 176 416
    WIRE 240 624 176 624
    WIRE 400 16 304 16
    WIRE 400 192 304 192
    WIRE 400 368 304 368
    WIRE 400 576 304 576
    WIRE 496 16 464 16
    WIRE 496 192 464 192
    WIRE 496 368 464 368
    WIRE 512 576 464 576
    WIRE 608 16 576 16
    WIRE 608 192 576 192
    WIRE 608 192 608 16
    WIRE 608 368 576 368
    WIRE 608 368 608 192
    WIRE 608 576 592 576
    WIRE 608 576 608 368
    WIRE 672 192 608 192
    WIRE 672 224 672 192
    FLAG 304 112 0
    FLAG 304 288 0
    FLAG 304 464 0
    FLAG -16 704 0
    FLAG 672 304 0
    FLAG -112 240 0
    FLAG 304 672 0
    SYMBOL diode -32 368 R0
    WINDOW 0 51 16 Left 0
    WINDOW 3 34 41 Left 0
    SYMATTR InstName D1
    SYMATTR Value 1N914
    SYMBOL diode -32 256 R0
    WINDOW 0 46 16 Left 0
    WINDOW 3 32 43 Left 0
    SYMATTR InstName D2
    SYMATTR Value 1N914
    SYMBOL diode -32 144 R0
    WINDOW 0 56 21 Left 0
    WINDOW 3 41 47 Left 0
    SYMATTR InstName D3
    SYMATTR Value 1N914
    SYMBOL diode -32 32 R0
    WINDOW 0 51 24 Left 0
    WINDOW 3 38 51 Left 0
    SYMATTR InstName D4
    SYMATTR Value 1N914
    SYMBOL res 160 112 R90
    WINDOW 0 0 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName R1
    SYMATTR Value 2.2k
    SYMBOL res 160 224 R90
    WINDOW 0 0 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName R2
    SYMATTR Value 2.2k
    SYMBOL res 160 336 R90
    WINDOW 0 0 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName R3
    SYMATTR Value 2.2k
    SYMBOL npn 240 368 R0
    SYMATTR InstName Q1
    SYMATTR Value 2N3904
    SYMBOL npn 240 192 R0
    SYMATTR InstName Q2
    SYMATTR Value 2N3904
    SYMBOL npn 240 16 R0
    SYMATTR InstName Q3
    SYMATTR Value 2N3904
    SYMBOL LED 464 352 R90
    WINDOW 0 0 32 VBottom 0
    WINDOW 3 72 32 VTop 0
    SYMATTR InstName D5
    SYMBOL LED 464 176 R90
    WINDOW 0 0 32 VBottom 0
    WINDOW 3 72 32 VTop 0
    SYMATTR InstName D6
    SYMBOL LED 464 0 R90
    WINDOW 0 0 32 VBottom 0
    WINDOW 3 72 32 VTop 0
    SYMATTR InstName D7
    SYMBOL res 592 0 R90
    WINDOW 0 0 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName R4
    SYMATTR Value 220
    SYMBOL res 592 176 R90
    WINDOW 0 0 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName R5
    SYMATTR Value 220
    SYMBOL res 592 352 R90
    WINDOW 0 0 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName R6
    SYMATTR Value 220
    SYMBOL voltage 672 208 R0
    WINDOW 0 -14 58 Left 0
    WINDOW 3 6 3 Left 0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V1
    SYMATTR Value 5
    SYMBOL voltage -112 144 R0
    WINDOW 0 -13 59 Left 0
    WINDOW 3 -51 138 Left 0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V2
    SYMATTR Value SINE(0 4 5)
    SYMBOL res -32 608 R0
    WINDOW 0 49 47 Left 0
    WINDOW 3 44 74 Left 0
    SYMATTR InstName R8
    SYMATTR Value 2.2k
    SYMBOL diode -32 528 R0
    SYMATTR InstName D8
    SYMATTR Value 1N914
    SYMBOL npn 240 576 R0
    SYMATTR InstName Q4
    SYMATTR Value 2N3904
    SYMBOL res 608 560 R90
    WINDOW 0 0 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName R9
    SYMATTR Value 220
    SYMBOL LED 464 560 R90
    WINDOW 0 0 32 VBottom 0
    WINDOW 3 72 32 VTop 0
    SYMATTR InstName D9
    SYMBOL res 144 464 R90
    WINDOW 0 0 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName R10
    SYMATTR Value 2.2k
    TEXT -146 362 Left 0 !.tran .1
    TEXT -216 200 Left 0 ;Audio
     
  6. Rob

    Rob Guest

    Wow, those posts are way above what i know right now, and no, i dont
    know of anywhere i can get those kind of parts here in belize. i know
    that with resistors you can change how an LED reacts when music is
    pumped through it, but i also know that you have the risk of damaging
    your speakers if you just hard-wire on an LED without any proper
    circuitry. I am just looking for a simple solution, maybe one that i
    could completely build everything out of scrap wires or the sort. I
    would appreciate that simplest of solutions. Thanks
     
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