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
I think you are going to need some resistors and a pot or two. Got those?
-- Welcome to the group. :-) You can\'t get resistors in Belize? Or comparators?
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
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
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.