Musical LED's

[Rob]

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.

 

[Michael Black]

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.

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

 

[BobG]

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

 

[John Fields]

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.

---
Welcome to the group.

You can't get resistors in Belize?

Or comparators?

 

[Mike]

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.

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

 

[Rob]

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