Making a simple LED music controller?

c4ppucino

Member
2014-12-24 1:50 pm
Hi everyone,

I don't know if this is the right sub-forum to ask, but here goes. So I'm pimping my PC with LEDs (old PC, just new casing and stuffs). I installed a neon flex strip around the frame, plugged to a remote LED controller. It worked nicely. Now I'm thinking of making the LED 'dance' to the music.

Here's the thing, I'm only using headphones with my PC, no speakers. Music LED controllers (ready to use) I found mostly use a built-in mic to listen to ambient sound. What I want is a controller that listens to the headphone jack (maybe with a 3.5mm jack splitter, or even solder it to the jack itself)

I'm thinking there are 2 different ways to approach this

- just on and off, by a simple relay. Might be able to do it with an SCR/transistor and a potentiometer for sensitivity control. I have built a homebrew photography flash gun sound trigger with a simple SCR in the past, so I'm familiar with the concept of SCR as a relay/gate.

- brightness control, gets brighter with louder sound/signal, and vice versa. Have no idea how to build from scratch.

So my question are:
1. Is there a site that contains the schematic to build the thingy I mentioned above? Also with the required parts (like what SCR part number, what size of potentiometer would work, etc)

2. Say I go ahead and buy the controller with the built in mic. Can I just snip off the built in mic, and wire it to the headphone output of my PC? I'm guessing it's not that simple, but I have minimal knowledge about these things.

Thank you in advance.
 
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It is easy.
Just use a simple single stage amplifier with the input to the head phone socket. To the output of this simple amplifier connect a 1K limiting resistor in series with a diode to the top of a pot.
Connect the wiper of the pot to the gate of a MOSFET out of an old computer power supply.
The drain will drive the LED string. If the LED string is 12 volt the whole thing will run from spare power connector.
You can later add further units with bass and treble boost to get full sound to light effects using normal tone control circuits with there pots hard wired with fixed resistors.
It is much easier than making those 1970s mains ones with triacs in them.
 

c4ppucino

Member
2014-12-24 1:50 pm
Hi, thank you for all the answers, and sorry for the late reply.

So I went and bought the LED music controller I mentioned above. I was thinking that maybe I could take off the built-in mic, and wire the terminals to the sound output of my PC.

Well, it didn't work, lol. I tested the thingy before I opened it up, and everything was working as it should. So I de-soldered the mic, and got 2 terminals on the pcb. Now the strange part was, even if I only touched one of the terminals with an open wire (not connected to anything), the LED started blinking randomly. I have recorded a video showing what I meant: YouTube

I'm guessing I'm missing a component in between the wire to the terminal? A transistor or something, maybe?

It is easy.
Just use a simple single stage amplifier with the input to the head phone socket. To the output of this simple amplifier connect a 1K limiting resistor in series with a diode to the top of a pot.

I kinda understand the idea, but no clue about the schematic, which leg goes to where, and the measurements of the components, etc.

Also, why do I need a single stage amplifier? Is the voltage from the audio jack not enough to open/close a transistor's gate?
 
The FETs in computer power supplies are almost all IRF640 or IRF840 clones and all have the same pin out. Just download a data sheet.

The maximum voltage is way above what you need but they work fine at all lower voltages.
It may well work with just a 10K resistor and a diode to the pot.
Any added distortion caused by loading from the diode circuit will be very low and is not likely to be noticed.
The data sheet says that the gate will take negative voltage so you may well be able to just connect the 10K resistor directly to the gate without a diode although a leak resistor may well be needed to stop the gate floating.
On a sound card the line output may be a better choice.
Your LEDs will have to share the negative power rail with the computer as it is connected to the sound card as well as the source lead on the FET.
The LED strip just goes negative to the drain on the FET and positive to the power supply. The fan power supply in the computer will give you enough power for a small 12 volt strip.
Just check the FET and if it gets warm fit it on a heat sink.
 

c4ppucino

Member
2014-12-24 1:50 pm
The FETs in computer power supplies are almost all IRF640 or IRF840 clones and all have the same pin out. Just download a data sheet.

Ok, I've ordered the components, just have to wait for them to arrive.

Meanwhile, I'm thinking of doing 2 version, this version (because it's simple), and modifying the LED music controller with the built-in mic.

Anybody have any idea on how to replace the built-in mic with an AUX input? As of now, even if I just touch one of the terminal with a blank wire, it will light up the LED, blinking randomly. I don't know if it's too sensitive or something.

Thank you.
 

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c4ppucino

Member
2014-12-24 1:50 pm
The FETs in computer power supplies are almost all IRF640 or IRF840 clones and all have the same pin out. Just download a data sheet.

The components arrived, and I tried assembling to the best of my understanding. Well, it didn't work though. I must be wrong somewhere.

I used an IRF840, and a 50k variable resistor. I didn't use any diode, because you said it may be able to work without a diode. I also don't have a breadboard, so I just soldered the stuffs with some jumper wires.

Tried using an aux cable, plugged to my phone, didn't work. Tried using an earphone amplifier in between, still didn't work. So where did I go wrong?
 

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The audio should go to the third terminal on the pot.
While you have got the wires off the gate try touching between the tab on the IRF840 and the gate with a wet finger. The LEDs should light up and then dim slowly. 12 volts will not bight you.
You can also drive the gate with a meter on diode test range.
Once the pot is connected correctly the LED will dim quickly.
 

c4ppucino

Member
2014-12-24 1:50 pm
The audio should go to the third terminal on the pot.
While you have got the wires off the gate try touching between the tab on the IRF840 and the gate with a wet finger. The LEDs should light up and then dim slowly. 12 volts will not bight you.
You can also drive the gate with a meter on diode test range.
Once the pot is connected correctly the LED will dim quickly.

Hi, not sure if I follow. If I connect the wires on the pot to the 2 furthermost posts, wouldn't the resistor value be constant (in this case, 50k)? Let's say the terminals are labeled A-B-C, which terminals should I connect the wires and the gate and drain to?

As of now (without changing anything from the picture above):
- when I plug in power, the LED lights up. I can't dim it by adjusting the pot
- when I plug in the audio jack, the LED dims. I can control the brightness a bit by adjusting the pot
- when I set the pot to barely dim light, and I play music, the LED lights up, but stays that way. When I pause the music, the LED stays that way for about 2-3 seconds, then go back dim

I built (soldered) it based on this schematic I found on youtube, with AUX input in place of the mic.
 

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c4ppucino

Member
2014-12-24 1:50 pm
Try a 10K pot and find out the resistor ratio needed for making an attenuator pad.
Remove also the Mic Bias resistor. (10K on the left perhaps, It should be connected to the supply).

Hi, thank you for the reply. I tried using a 50k pot, and the LED still blink randomly, even without anything connecting to it but the pot's terminal. Havent tried removing the 10K resistor on the PCB yet. I tried to find the route leading to the power supply, but I just couldn't. I just can't see which goes where on the PCB....

It's nicer when you have different LEDs responding to different frequencies:

The Electronic Peasant's LED Color Organ Page

Just leave out the first transistor stage.

Take care,
Doug

Hi, thanks for the link, but that one seems too complicated for me. I only know basic stuffs like resistors, PCB, soldering, etc :)