1

A few years ago (around 3 years) I've made a very basic circuit to make a led blink to the sound.

The circuit a single regulator connected to a USB port to extract 5V, with a 3.3V led, conected to a simple 3.5MM cable connected to the sound card, using the left channel.

This circuit worked great, but it was too weak and the sound would be very bad.
This is probably because the electrivity was being mixed with the audio signal.

I don't remember which regulator I've used, but it was one from an old TV, which would lose 0.5V below 12V, and worked with a minimum of 3V.

Posing this, what is the simplest sound-reacting led circuit?

To be a simple circuit, it must require the minimum amount of parts and must be easily assembled without a breadbord or prototype board.

My budget is incredibly low, so, I can't afford to buy and learn how to use a soldering iron, but if it is required I will try to find one.
If it isn't required, I would be really happy.

Optionally, this circuit may be made to work with a Molex connector, on the 12V rail, which I can easily find power supplies and cables to test it.

Ismael Miguel
  • 251
  • 1
  • 3
  • 12
  • What kind of sound do you want it to react to? battery+resistor+led easily reacts to excessive sound level of 180dB+ ... – PlasmaHH Feb 20 '15 at 15:47
  • Just a regular MP3 player, TV, audio player, cellphone or something that the average user uses to listen to music. I would love to actually connect it to a HD Audio connector on my motherboard and make one with an audio connection to connect to connect the cable and then connect the headphones/speakers on another end. So, it must be well below 100dB. – Ismael Miguel Feb 20 '15 at 15:47
  • Buy a soldering iron! Turn the sound into an electric signal (with a microphone), Gain up the signal level (with an opamp) so that it's large enough to turn on an LED (a few volts) and send into LED.. but you'll be disappointed by the results. You most likely want the LED to blink with the beat, which means some sort of filter in the signal chain.. and maybe a rectifier. – George Herold Feb 20 '15 at 15:53
  • @GeorgeHerold Won't that be.... Over-overkill? If I did with an old crappy regulator without a microphone, I may be able to do similar or better with better resistors and some other components to stop the sound to be crappy. At the moment, I can't buy one (I don't know where to buy here in Portugal) since I don't have money left this month. But I will next month. Maybe someone will offer one to me on my birthday (I highly doubt that). – Ismael Miguel Feb 20 '15 at 15:57
  • So you don't want to use a microphone to detect the audio, you want to hook into the audio signal itself? Not sure what you meant with your previous design. Did you use the left channel as the ground of the LED? Did the left channel lead to a transistor? – I. Wolfe Feb 20 '15 at 16:05
  • There's a bunch of circuits on the interwebs that feature a power transistor (eg. the venerable TIP31) driving an LED, sometimes with no resistors at all. I can't really recommend one over another or any of them at all, actually, you're likely to burn stuff up. – Spehro Pefhany Feb 20 '15 at 16:05
  • @I.Wolfe Yes, I want to hook it directly into an audio source. I've connected the left channel (positive) to the regulator along with the power and the led. I'm not sure how, but I think that the 1st pin was the power, the middle one was the sound and the 3rd was the led positive wire. – Ismael Miguel Feb 20 '15 at 16:11
  • @SpehroPefhany I'm aware of many of those circuits, but they have parts I can't buy in a store here or parts that I know how they work. And honestly, I want to keep my stuff away from fires. – Ismael Miguel Feb 20 '15 at 16:12
  • 2
    @IsmaelMiguel Nothing simpler is possible, in fact those are **too** simple. Perhaps you should just buy something and have it shipped to you- there's probably something on eBay etc. for $5 or less. – Spehro Pefhany Feb 20 '15 at 16:19
  • Ohhh, when you say regulator do you mean transistor? That would make more sense. So the left channel was turning the transistor on at the base. I could see a number of reasons that that could provide a less than ideal LED output depending on the design. As far as simple goes that's about as simple as it gets. Probably would want to get help on how to set it up though. Perhaps instead of such a vague question you could provide your old setup and ask for improvements. Or preferably spend some money for something more complex but better. – I. Wolfe Feb 20 '15 at 16:29
  • @SpehroPefhany The idea was to make my own. I don't even have account on eBay. Yes, it would be easier to buy it made by someone else, but it would also be so much more expencive and I would learn absolutely nothing too. – Ismael Miguel Feb 20 '15 at 16:39
  • @I.Wolfe Yeah, sorry the name swap :/ My old setup was simply a mesh of wires connected to a transistor. I don't even remember how I did it myself. Since I threw away the transistors, I was looking for a simple way to rebuild it. I don't mind to build something more complex, but for now I want the most simple circuit. Which then I may improve. – Ismael Miguel Feb 20 '15 at 16:41
  • You can't afford a dollar store soldering iron? – Passerby Feb 20 '15 at 16:43
  • @Passerby I don't live in the USA. I live in Portugal. So, no, I can't *right now*. Also, with shipping, that would be a massive cost for something that 'cheap' there. – Ismael Miguel Feb 20 '15 at 16:45
  • 1
    Hmm, well, a pound shop? Lojo de euro? My point is that a soldering iron can be found for very cheap. – Passerby Feb 20 '15 at 17:36
  • @Passerby Actually, its `loja`, but you were really close. I give you credits for that. In my city, I've never seen a place to buy electronic components. I will try to see somewhere close where I can buy such things. I know those are very cheap, but also rare in my zone. – Ismael Miguel Feb 20 '15 at 17:40
  • @tcrosley Actually, the idea is **totally** different. I'm asking a simple circuit to do the same. The volume doesn't matter. The voltage matteers a little, but not much. Also, I want it to work for higher voltages like 5v or 12v. – Ismael Miguel Feb 20 '15 at 19:49
  • Sorry, I realized my mistake a few minutes after voting to close. I then retracted my close vote. I forgot to delete the comment which is automatically generated by the system. – tcrosley Feb 20 '15 at 20:24
  • @tcrosley It's alright, we all make mistakes. Sadly, it won't be opened again. Unless we beg on meta, which might be useless. But thank you for reverting the close vote. – Ismael Miguel Feb 20 '15 at 20:48
  • Not sure what you mean. This question hasn't been closed, in fact there currently are no votes to close. One person cannot close a question, unless they are a moderator (which I am not). – tcrosley Feb 20 '15 at 20:51
  • @tcrosley http://i.imgur.com/iMnpiar.png It's showing as closed on my computer. – Ismael Miguel Feb 20 '15 at 21:04

2 Answers2

1

OK since you already have it as an electrical signal you might try something like this.

schematic

simulate this circuit – Schematic created using CircuitLab

George Herold
  • 4,754
  • 1
  • 18
  • 25
  • I don't understand much, but I can search the symbols. Is the sine 1kHz the audio source? – Ismael Miguel Feb 20 '15 at 16:33
  • Yeah, the sine wave is your source.... If you don't understand LED's and resistors. Well there is a whole wide world of electronics out there waiting for you. (The D's are your LED's) – George Herold Feb 20 '15 at 16:35
  • I assume the `R` is a `resistor`. But now, where is the power source to power the leds? – Ismael Miguel Feb 20 '15 at 16:37
  • The source of power is your sound card which I assume has enough power to run a small speaker (30 ohms or something.) OK forget the soldering iron and first by a book about learning electronics. – George Herold Feb 20 '15 at 16:43
  • Actually, my card can be regulated to 60 ohms. It's an Asus Xonar DG. I won't be using it exclusively for *this* card, but also to other things. It can be a TV, a cellphone, a radio, anything with a sound exit. The idea to buy a book is great, but first I need to find a good place to buy a reliable book. Since I don't live in the USA, that means that I'm left with little choices. – Ismael Miguel Feb 20 '15 at 16:46
  • I agree with George. Figure out the basics of the world that you're trying to work in, and then the answer should be easy. (And it should be obvious why your first version sounded so bad.) Since you clearly have internet, and you say you can't buy a book, try Google. – AaronD Feb 20 '15 at 17:30
  • @AaronD My first version sounded bad because it was leaking electricity to the sound channel and I was using a mesh of wires connected to a transistor, instead of a simple pcb with a properly assembled circuit. At least, that is my theory. I guess this could be easily fixed with a diode. I don't really know for sure. – Ismael Miguel Feb 20 '15 at 17:59
  • Umm...right...you don't know. Hence George and my points. By the way, that's not the reason at all, if I understand your post correctly. I'd ask for a schematic to clarify, but you said you don't use those. Therefore, lesson #1 should probably be to ask Google how to read and write electrical schematics. Yippee!!! :-D – AaronD Feb 20 '15 at 18:04
  • @AaronD The big problem isn't that. I'm a programmer and I can write programs in any language as long as I know the basics of that said language. Same must be for electric schematics. The problem is that I don't even remember *exactly* the 'circuit' (it was a mesh of wires connected somewhere that somehow it worked). I don't remember the transistor (I threw it away last month) and where each wire was in. I will try to get a good book. Can you provide me with the name of a good free book? (It may be in English or Portuguese, but must be free because I have no money and credit card). – Ismael Miguel Feb 20 '15 at 18:10
  • 1
    Hmm. The words "good", "free", and "physical" usually don't go together. But as long as your internet stays on, you can wander around here: http://sound.westhost.com/index2 He only wants the front page to be shared directly so that people can find the *entire* site, but if you go to Articles and scroll down, you'll find the beginners' section in the middle. (Why it's not on top, I don't know, but there it is.) – AaronD Feb 20 '15 at 18:24
  • @AaronD The begginners' section isn't for begginners... (at least the first link) But I did took a very quick look. I will try to read it all today. Sadly, can't practice much today (since I lack the material). I've also found out I can't buy anything since there is nothing close (within 10km from me) that sells electronic material. Since I don't own a car, this is quite cumbersome since I can't go on foot to buy a few leds or transistors or even a breadboard to test. But thank you a lot for the link. – Ismael Miguel Feb 20 '15 at 18:33
  • 1
    @IsmaelMiguel you could try this website for electronics information. It has a lot of handy information and schematics. http://www.talkingelectronics.com/te_interactive_index.html – Delta1X Feb 20 '15 at 18:45
  • @Delta1X Wow, That website looks like the 90's! But I will take a deep look into that one as well. Thank you a lot for your link! – Ismael Miguel Feb 20 '15 at 18:50
1

Because you want the LED to react to audio from a MP3 player or similar, I suggest that you have a look at a recent thread on this forum: 155914. I showed a circuit that uses 2 transistors: one transistor is wired as a diode and biases the 2nd transistor just below its' turn ON point. It should work well for you.

Community
  • 1
Dwayne Reid
  • 23,390
  • 2
  • 35
  • 67
  • It isn't properly simple, but it looks really good. I still have to learn what everything means, but it does look good. I'm not worried about lower volumes. If it could be made simples, I would stand up and clap. But it brings me one problem: power source. If it is only 3V, I can't use with a USB conector or inside my computer connected to the 5V or 12V of the Molex connector. I could try with a SATA connector, but not every single power supply has those. But I like your solution. But just one question: Won't the voltage leak though the capacitor to the input and cause crappy audio quality? – Ismael Miguel Feb 20 '15 at 17:46
  • No. Two things happening here: the capacitor keeps the DC where it belongs *and* the series resistor provides much higher input impedance compared to the very low output impedance of your headphone jack. – Dwayne Reid Feb 20 '15 at 20:37
  • I can always crank up the amplifier in my card to provide more power through the sound cable. My card has a special setting for headsets with 60ohms. It should do it. – Ismael Miguel Feb 20 '15 at 20:50
  • If it is closed, it says [on hold] after the title. – tcrosley Feb 20 '15 at 21:18
  • @tcrosley You answered on the wrong place (I think). But it isn't saying anymore what I shown you on the comment. – Ismael Miguel Feb 20 '15 at 21:45